SYSTEMATIC CONSIDERATION OF RECENT TOOTHEDWHALES BASED ON THE MORPHOLOGY OF
TYMPANO-PERIOTIC BONE
TOSHIO KASUYA
Ocean Research Institute, University of Tokyo

ABSTRACTThe tympano-penotic bones of recent Odontoceti have attained wide
variety of morphological peculiarities. The individual and sexual variations,and the bilateral asymmetry of this part are considered to be small. Though
it is possible to identify most of Odontoceti species based on the morphology of tympano-periotic bones, it is usually difficult to do the Delphininae
species. Considering the several series of specialization observed in various
characteristics of tympano-periotic bone, its process of evolution and the phylogenetic relationships of Odontoceti species are discussed.
CONTENTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1Materials and method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2Growth and bilateral symmetry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6Morphology of tympano-periotic bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Biometrical between-species similarity of tympano-periotic bone . . . . . . . . 44
Evolution of tympano-periotic bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
INTRODUCTION

Though the taxonomical or morphological study of tympano-periotic bone have been
made on some fossil species (Kellogg, 1931, 1955, 1957, 1965) or on recent species(Yamada, 1953) and the morphological variety is reported, the systematics of the
toothed whales have been based mainly on the skeletal and external characteristics
and less importance was put on the morphology of tympano-periotic bone. However, as the tympano-periotic bones of toothed whales are considered to haveestablished a special adaptation for the underwater acoustics and have attained various morphological peculiarities, the morphology of this part seems to be useful in thetaxonomy of Odontoceti.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973, 1-103.

2

KASUYAThe present study intends to re-examine the systematics of toothed whales
based on the morphology of the tympano-periotic bones, and to throw some lightupon the classification of toothed whales. The knowledge on the morphology andindividual variation of tympano-periotic bone, obtained in this study, will offersome key to identify the species or genus by means of tympano-periotic bone.
MATERIALS AND METHOD
The materials used in this study are shown in Table 2, which comprise 313 individuals in 30 genera. They are mostly composed of the specimens collected by me orprof. M. Nishiwaki of the Ocean Research Institute, and are kept in the Ocean
Research Institute, University of Tokyo. Other than these specimens, some werekindly offered by various persons and institutes shown in Table 1.

Fig. 1. Tympano-periotic bone of Platanista gangetica, showing the morphologicalterms used in this report. AC, Aperture of aquaeductus cochleae. AF, Internal
aperture of aquaeductus Fallopii. AO, Accessory ossicle. APP, Anterior processof periotic. AS, Anterior spine. C, Conical process. GP, Cochlear portion.
CFN, Canal for facial nerve. CSM, Canal for stapedial muscle. GT, Crista
transversa. DEL, Aperture of ductus endolymphaticus. EF, Elliptical foramen(see Fig. 2). FIAM, Fundus of internal auditory meatus. FR, Foramen rotunda.
FS, Foramen singulare. IP, Inner pedicle. IPN, Interprominential notch. IPP,
Inner posterior prominence. IV, Involucrum. LF, Lateral furrow. LTA, Lower
tympanic aperture. MF, Median furrow. OP, Outer pedicle. OPP, Outer
posterior prominence. PPP, Posterior process of periotic. PPT, Posterior
process of tympanic bulla. SP, Sigmoid process. SUP, Superior process. TO,
Triangular opening. TSF, Tractus spiralis foraminosus. UTA, Upper tympanic
aperture. VK, Ventral keel.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONESTABLE I. LIST OF INSTITUTES AND PERSONS, WITH ABBREVIATIONS,WHO OFFERED THEIR SPECIMENS FOR THE PRESENT STUDY
American Museum of Natural History, New York C. USA, R. G. Van Gelder
AMNH
Ayukawa Whale Museum, Ayukawa Japan, N. Kimura
AWM
Carl L. Hubbs, Scripps Inst. Oceanography, Univ. of Calif., San Diego USA
CLH
Chicago Natural History Museum, Chicago USA, .J.C. Moore
CNHM
Dale W. Rice, Fish and Wildlife Service, Seattle USA
DWR
EML
Enoshima Marineland, Enoshima Japan, M. Nakajima
Hung-cha Yang, Taiwan Fisheries Res. Inst., Formasa.
HCY
National Science Museum, Tokyo Japan, Y. Imaizumi
NSM
Los Angeles County Museum of Natural History, Los Angeles USA, D. K. Caldwell
LACM
Museum of Vertebrate Zoology, Univ. of Calif., Berkeley USA, S. B. Benson
MVZ
Faculty of Fisheries, Nagasaki Univ., Nagasaki Japan, K. Mizue
NUF
Faculty of Medical Science, Nagasaki Univ., Nagasaki Japan, K. Mizue
NUMS
SDNHM Natural History Mmeum, San Diego USA, R. D. Mason
Ocean Research Inst. Univ. of Tokyo, Tokyo Japan, M. Nishiwaki and T. Kasuya
TK
Taiji Whale Museum, Taiji Japan, T. Higashi
TWM
United States National Museum, Washington D. C. USA, C. 0. Handley
USNM
Marineland of the Pacific, Los Angeles USA, W. A. Walker
WAW
Zoological Survey of India, Calcutta India, D. K. Ghosal
ZSI

TABLE 2.

Number of individuals
5 from the Brahmaputra (4TK and lZSI specimens)
2 from India (USNM 172409, 23459)
Inia geoffrensis
5 from the Amazon (LACM19588, 19589, !9590, USNM239667, 45982)
Lipotes vexillifer
l from Tunting Lake (AMNH57333)
I (USNM 49494)
Pontoporia blainvillei
16 from Japan (l 4NUMS and 2TK specimens)
Neophocaena phocaenoides
l from China (USNM 240862)
2 no locality (AMNH57332, USNM239990)
Phocoena ph. vom£rina
3 from the North Pacific (MVZ21509, 97900, USNM274588)
3 from the North Atlantic (AMNH21514, TK84, USNM36591)
Phocoena ph. phocoena
Phocoena sinus
1 from California Bay (SDNHM20688)
Phocoenoides dalli
6 f10mJapan (6 TK specimens)
Phocoenoides truei
6 from Japan (6 TK specimens)
Delphinus bairdi
5 from California (DWR988, TK150, SDNHM 20140, 21204, 21209)
1 from Formosa (TK255)
2 from the Atlantic (USNM21525, 1 TK specimen)
Delphinus delphis
Lagenorhynchus obliquidens 11 from north east Japan (TK sepcimens)
3 from California (DWR3768, LACM F355, USNM21218)
Lagenorhynchus acutus
3 from the west Atlantic (USNM14229, 14265, 20960)
Lagenorhynchus albirostris 3 from the west Atlantic (AMNH143520, CNHM 30522, TK87)
1 from New Zealand (AMNH34935)
Lagenorhynchus obscurus
Lagenorhynchus australis
1 from Chiloe I., Chile (CHNHM22248)
7 from Japan (TK specimens)
Steno bredanensis
Lissodelphis borealis
3 from Japan (TK205, 257, 258)
3 from the north east Pacific (DWR1965-2, 1965-3, USNM270981)
Stenella caeruleoalba
15 from Japan (TK specimens)
Stenella styx
1 from the Atlantic (TK specimen)

No. Speciesl Platanista gangetica
2

3
4
5

6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

LIST OF MATERIALS USED IN THIS STUDY

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

3

4

KASUYATABLE 2. (continued)(?) Stenella roseiventris
4 from Japan (NUF specimens)(Hawaiian spinner dolphin) 2 from Hawaii (DWRl 194, TK50)
23 (?) Stenella longirostris
2 from the east Pacific (SNHM21199, WAW52)(Eastern Pacific spinner dolphin)
24 Stenella attenuata
7 from Japan (TK specimens)
24a Stenella graffmani
3 from the east Pacific (DWR1965-l, SENHM 20637, WAW44)
24b Stenella plagiodon
3 from the north Atlantic (AMNH38206, 63779, USNM292070)
25 Tursiops truncatus
43 from Japan (19 EML specimens, 24 TK specimens)
25a Tursiops truncatus
3 from the west Atlantic (MVZ23705, 23708, USNM16504)
26 Tursiops gilli
2 from California (SDNHM20143, 20144)
27 Cephalorhynchus spp.
1 from Forkland (USNM252568), 1 from Chile (USNM 21167)
1 from the Amazon (AMNH94169, S . .fl,uviatilis)
28 Sotalia ~pp.
1 (CNHM34907, S. guianensis)
29 Sousa teuszii
1 from Senegal (TK260)
30 Pseudorca crassidens
2 from the north Atlantic (USNMl 1320, 218360)
2 from the north Pacific (TK specimens)
31 Orcinus orca
5 from the north Pacific (DWR832, 986, 2TK specimens, TWM
specimen), 2 no locality (LACM781, USNM219326)
32 Peponocephala electra
6 from Japan (TK specimens)
33 Feresa attenuata
7 from Japan (TK specimens)
34 Globicephala melaena
4 from the north Atlantic (AMNH180143, USNM14044, 20457,
lTK specimen)
35 Globicephala macrorhyncha
26 from Japan (TK specimens)
36 Grampus griseus
11 from Japan (8EML specimens, 3 TK specimens)
1 from the Atlantic (USNM22446)
37 Orcaella brevirostris
1 from Borneo (USNM199743), 1 no locality (ZSI274)
38 Delphinapterus leucas
4 (AMNH180017, SDNHM20046, USNM7536, 215015)
39 Monodon monoceros
4 (AMNH63987, 73318, SDNHM7096, USNM267960)
40 Berardius bairdi
5 from the north Pacific (LACM1964, MVZ125602, TK299, 300,
USNM49727)
41 Berardius arnouxi
1 from New Zealand (USNM2151 l)
1 from Norway (USNM14449)
42 Hyperoodon ampullatus
43 Mesoplodon stejnegeri
7 specimens (AMNH18531 l, 143829, MVZ130250, TK97, 365,
USNM143132, 286826)
44 Mesoplodon densirostris4 specimens (AMNH139931, 69579, TK256, HCY specimen)
45 Mesoplodon ginkgodens
2 specimens (NSM specimen, HCY specimen)
46 Mesoplodon europaeus
3 specimens AMNH121894, 90051, USNM306302)
47 Mesoplodon carlhubbsi
2 specimens (AWM specimen, USNM274591)
48 Mesoplodon mirus
1 specimen (AMNH174293)
49 Z,iphius cavirostris
6 from the north Pacific (MVZ129645, SDNHM 19558, USNM
20993, 3TK specimens), 1 no locality (USNM21975)
50 K ogia breviceps
5 specimens (CHL specimen, LACM RLB145, TK244, SDNHM
20139, SDNHM-)
51 Kogia simus
5 specimens (LACM RLB240. TK47, 49, TK specimen, USNM
22015)
52 Physeter catodon
8 specimens (3 NUMS specimens, TK301, 302, 303, 304, USNM
49488)
22

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

5

The materials are usually grouped into the species, but in some cases into smaller
units considering the locality. In the genera as Cephalorhynchus and Sotalia, where
only few samples are obtained and the taxonomy is not fully established, the samples
are dealt combining into the genus.
The measurement and general observation were made on 21 points shown in
Fig. 2 and Table 3. The measurements are usually made on a straight line connecting the two points to nearest 1/10 mm, with a caliper of 1/20 mm accuracy, andif available on both sides. In the calculation of the mean value and other statisticalanalysis of the measurements, measurements of one side were randomly selected.
But in the analyses of Growth and bilateral symmetry and of the largest and smallest
range of the measurement, all the available measurements were included.

13r----15,----;

Fig. 2. Measurements used in this report, for the explanation see Table 3. The
contour of the tympano-periotic bone is based on that of Stenella. For EF see
Fig. 1.

The anatomical terms are conformed mainly to Kellogg (1936) and partly to
Yamada (1953 ), but some terms are newly introduced in this report. All of theseterms are shown in Figs. 1 and 2.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

KASUYA

6
TABLE 3.

POINTS OF MEASUREMENTS AND OF OTHER GENERAL OBSERVATIONS

Tympanic bullaStandard length of tympanic bulla, distance from anterior tip to posterior end of outer posterior
prominence
2. Distance from anterior tip to posterior end of inner posterior prominence
3. Distance from postero-ventral tip of outer posterior prominence to tip of sigmoid process
4. Distance from postero-ventral tip of outer posterior prominence to tip of conical process
5. Width of tympanic bulla at the level of the sigmoid process
6. Height of tympanic bulla, from tip of sigmoid process to ventral keel
7. Width across inner and outer posterior prominences
8. Greatest depth of interprominential notch
9. Width of upper border of sigmoid process
10. Width of the posterior branch of lower tympanic aperture
11. Presence of elliptical foramen. If present, its greatest diameter
12. The thicker side between outer and inner posterior prominences
l.

13.
14.
15.
16.
17.
18.
19.
20.
21.
22.

Periotic
Standard length of periotic, from tip of anterior process to posterior end of posterior process,measured on a straight line parallel with cerebral border
Thickness of superior process at the level of upper tympanic aperture
Width of periotic across cochlear portion and superior process, at the level of upper tympanic
aperture
Least distance between the margins of fundus of internal auditory meatus and of aperture ofductus endolymphaticus
Least distance between the margins of fundus of internal auditory meatus and of aperture ofaquaeductus cochleae
Length of the articular facet of the posterior process of periotic for the posterior process of tympanicbull aAntero-posterior diameter of cochlear portion
Presence of sutural connection between the posterior processes of tympanic bulla and of
periotic
Presence of the sutural connection between posterior process of tympanic bulla and squamosal
Length of periotic shown by the percentage of length of tympanic bulla

GROWTH AND BILATERAL SYMMETRY

Bilateral symmetry
The bilateral comparizon of tympano-periotic bones was made on 6 species ofDelphinoidea, Neophocaena phocaenoides, Stenella caeruleoalba, Lagenorhynchus obliquidens,
Tursiops truncatus (from the coast of Japan), and Grampus griseus, on the standard
length (measurement nos. 1 and 13) and on the other measurements shown by thepercentage of the standard length.
On each particular points, mean of the remainder of the right value minus theleft were calculated, then the significance of its deviation from 0 was examined witht table. This result shows that most of the observed bilateral asymmetry is not
significant. But as shown in Table 4, the bilateral deviation in some measurements
is so large that can be expected with the probability less than 2% and is suggested tobe significant. But if the deviation between the mean values of both sides are examined, neglecting the individuals, there can be expected no significant bilateralSci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

7

asymmetry. This is because the bilateral asymmetry in each individuals is smaller
comparing with the individual variation. As the result it is concluded that, inspite of the possibility of bilateral asymmetry on some part of the tympano-periotic
bone, it will not lead to the erroneous result to neglect it and to select randomly
the right or left side in the calculation.
TABLE 4.

SOME MEASUREMENTS OF TYMPANO-PERIOTIC BONES
WHERE BILATERAL ASYMMETRY IS EXPECTED.
FOR MEASUREMENT NO. SEE TABLE 3.

SpeciesNo. of themeasurement

Samplesize

Range ofmeasurement

Mean of theright minus left

Probability

N. phocaenoides
N. phocaenoides
S. caeruleoalba
T. truncatus
Gl. macrorhyncha
Gr. griseus

3
8
10
13
3
17

11
14
7
37
23
4

74.8-83.2
10.4-17 .8
2.2- 5.8
31. 7-37 .8
57.1-73.6
46.8-58.6-0.773-0.5640.421-0.908-2.1651.150

0.02-0.01
0.01>
0.02-0.01
0.02-0.01
0.02-0.01
0.02-0.01

Growth of tympano-periotic bone
To obtain a general feature of the growth of tympano-periotic bone of toothed
whales, the growth of tympano-periotic bone accompanied with the growth of theanimal and its relative growth were studied on 4 species of Delphinoidea, or Globicephala macrorhyncha, Tursiops truncatus, and Neophocaena phocaenoides. In Figs. 3-57,
if available, the measurements of the both sides are plotted.
Generally speaking the standard length of tympanic bulla slightly increases inparallel with the growth of the animal, but that of periotic shows almost no increase.
The proportional dimensions of tympano-periotic bone show rather wide individual
variation. As observed in these figures, the sexual difference is not expected.
Globicephala macrorhyncha
Tympano-periotic bones from 26 individuals are used here, among which thesex and body length are known on 23 individuals.
The tympanic bulla of this species has conspicuous anterior spine, ventral keel,
and posterior process. These characters seem to be formed soon after birth. As
shown in Pl. XXVII the anterior margin of the tympanic bulla of adult individual
has a plate-like anterior spine. The corresponding part of two newborn calves of
138 cm ( d') and 141 cm ( d') in body length is smooth and has no anterior spine.
But the spine is formed on a juvenile female of 203 cm in body length. In the two
newborn calves, the ventral keel is not developed, but retains only a granulated
structure. But this granulated area is changed, in the 203 cm female, into a usual
ventral keel observed in the adult. The shape of the posterior process of the newborn calves is short, and round and resembles that of adult Phocoenidae. But it
develops longer, in the 203 cm female, and attains the form of a long spongy process
directing postero-laterally.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

KASUYA

8

..

~40

0

.!;

<">38
6
.t
c:

0

200

300

400

200

Body length in cm

300

400

Body length in cm

Fig. 3. Globicephala macrorhyncha. Relation between
body length and length of tympanic bulla (meas·
urement no. 1). Triangle indicates male, circle
female. In both sexes closed mark indicatesthe left side, and open the right.

Fig. 4. G. macrorhyncha. Relation between bodylength and length of periotic (measurement no.
13). For marks see Fig. 3.

.s::.

.s::.
°'c: 70

E

gis5

E

~

+

0 90

•

QI

A

~

0

•

':. •

~ ......... iso ..... i lt,. ,. . .

............

•

40---- 4 • + ••AA

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8'. 55 --------------------------------------..._______...,________,~------::-!-=----'32
35
40
45
50

35

Length of tympanic bulla in mm

40

45

E

E

31
0

27

50

Length of tympa.nic bulla in mm

Fig. 5. G. macrorhyncha. Measurement no. 2 Anterior tip of tympanic bulla to inner posterior
prominence. Cross mark indicates the sex unknown, solid line average percentage, and dottedline the length re-calculated from the average
percentage. For other mark• see Fig. 3.

Fig. 6. G. macrorhyncha. Measurement no. 3 Tipof sigmoid process to outer posterior prominence.
For marks see Fig. 5.

.s::.52.s::.58c:
41-54"\ 1i- 0c.c:......~.....~···.

~48

0

0

~40

0

.

~I.I.

c

~

•

o

•

..

------------ .. --- ----- ---___ ..................... ----40

45+• .......__

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E
E

22

1.....------"=------='=:-------.h..--~ 18

35

o+

0

•

o•

41

41

°'

•t·~

50

•••

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~

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--...........°' ••• • ~·~.

I -------------------------::.-~
46

..

E
E

22

'--~~~---''--~~~--'~~~~~~-=· 18

35

40

45

50

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 7. G. macrorhyncha. Measurement no. 4 Tipof conical process to outer posterior prominence.
For marks see Fig. 5.

Fig. 8. G. macrorhyncha. Measurement no. 5 Widthof tympanic bulla. For marks see Fig. 5.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

..c81
'6i
c:
.!!75
0

£50

.;~+1+
0 e+

:46

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0

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a.

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CLI

CLI

9

CLI

E
E

---- ------------- -----------· -. --------··

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..................................

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21

-------- ------------------

3~5===-~7
40=-~~-4~5=---"-~-5~0~-l 29

3~5~~~-4~0~~~-4~5~~~-5~0~-1 17

Length of tympanic bulla in mm

Length of tympanic bulla in mrn

Fig. 9. G. macrorhyncha. Measurement no. 6
Height of tympanic bulla. For marks see Fig.
5.

Fig. 10. G. macrorhyncha. Measurement no. 7
Width across posterior prominences. For marks
see Fig. 5 .

..c 13'6ic:.!! 11
0
~9
111
'ECLI

++

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a.

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--..------------------------------------------

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-----------------------~-------------·-------

3~5~~~~4~0~~~~4~5~~~~-5~0~--'Z

3~5~~~740=-~~-4~5=--~~~5~0~-' 5

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 11. G. macrorhyncha. Measurement no. 8
Depth of interprominential notch. For marks
see Fig. 5.

Fig. 12. G. macrorhynclza. Measurement no. 9
Width of upper border of sigmoid process. For
marks see Fig. 5.
.<:

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'6i
c:
.!! 6
0

4>
D>

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g>95
~

u

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4~

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---..=..-..'II"~·-.
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3~5~~~-4~0~~~-4~5~~~-5~0~__.o+• •+ 0: ............

72 ____________________ : ___

et

E
E

~-:~•+OA ...

~

38
34

35

40

45

50

Length of tympanic bulla in mm

Length of tympanic bulla· in mm

Fig. 13. G. macrorhyncha. Measurement no. 10
Width of posterior branch of lower tympanic
aperture. For marks see Fig. 5.

Fig. 14. G. macrorhyncha. Measurement no. 13
Length of periotic shown in percentage of measurement no. 1. For maeks see Fig. 5.

On the periotic, the needle-shaped processes on the dorsal surface of superior
process and around the fundus of internal auditory meatus are one of the characteristic features of this species. This structur is considered to be formed in the latter
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

KASUYA

10

.c 68

.c 73

.!! 600.!! 69
0

c.
c

c.
c

Cl>

~52

E
E

'ECl>

18

~ 44

~

-----------32

34

36

38

40

~65

E
E

'ECl>

~ 61

26

~

15

32

Length of periofic in mm

34

36

40 22

38

Length of periofic in mm

Fig. 15. G. macrorhyncha. Measurement no. 14
Thickness of periotic. For marks see Fig. 5.

Fig. 16. G. macrorhyncha. Measurement no. 15\Vidth of periotic. For marks see Fig. 5.

.c 8

.c 16

c.
c:

c.
c:

.!! 6
0

+

. ••
. .• . •"'-

,+

Cl>

0

~

Cl>

0

0

Cl>

~8

ot

en 4
ra

cCl>

.!!12

0

0

,+

0

+.

0

2

+
+

a.

------- ----~-------------------------

34

32

36

'ECl>

E
E

38

40

Length of periofic in mm

~

~

2

••

•

y•

+

E
E

•+o

+ootRi~i;g..... ~
. . .6~

4°

Fig, 17. G. macrorhyncha. Measurement no. 16
Fundus of internal auditory meatus to ductus
endolymphaticus. For marks see Fig. 5.

+

+

~

4

0

-------'----·----------~-----E--------------~-- ...

32

34

36

38

40

Length of periofic in mm°

Fig. 18. G. macrorhyncha. Measurement no. 17
Fundus of internal auditory meatus to aquaeductus cochleae. For marks see Fig. 5 .

.c

g.52
.!!
0 48
Cl>

~·

•

.e •

E
E

•o+~·
oo 6
+
•

................

+
+

•
'

00

~

0

o•

0

•

+

~

20

.............. 0---;---------..............: .... ,. .................... ..

32

34

36

38

40

16

en
ra
~44
u
._
Cl>

a.40

E
E

----------------- --------------- -------------

18"--:::'='"""~~-'-~"'----l..~--L-~'--------1..~--L-~14

32

34

36

38

40

Length of periofic in mm

Length of periofic in mm

Fig. 19. G. macrorhyncha. Measurement no. 18
Length of facet on posterior process of periotic.
For marks see Fig. 5.

Fig. 20. G. macrorhyncha. Measurement no. 19
Diameter of cochlear portion. For marks see
Fig. 5.

part of the growth, as this is observed, in the females, on the animal more than
350 cm in body length.
The relations between body length and length of tympano-periotic bone areshown in Figs. 3 and 4, and those between the lengths of tympano-periotic bone
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

11

TYMPANO-PERIOTIC BONES
E
E.

·::::~• t~f1
c
•
0

i

111

....~ 36

g

~·
6

•

o

~!a

It

g

•

I

i

"'
"':;
"'

Ill

Ill

0

~2
~o~o_,__,__.__._2~s-o-'--'-~-"-3~0-o....___,__,_,

nl~

Body length in cm
Fig. 21. Tursiopstruncatus. Relation between bodylength and length of tympanic bulla (measurement no. 1). For marks see Fig. 3.

..

I..c 98

Ji.

• 0

4

•

°'
0

c
~94

~.

a,s...~.

60-.. &o~~·•

oo\ ~ e 'f

A

o

/J.

E
E

i

"'~90

c

.,.,

"'~ 8640.......

________ ..........................

34

--

36

38

36

40

250

300

Body length in cm

Fig. 22. T. truncatus. Relation between bodylength and length of periotic (measurement no.
13). For marks see Fig. 3.

•-o

..c

.+

.§ 72

0

0

"'ra

•

'\'

•

•li4

0

. .

4

Cl

~68

f>A

0

"' 66

.t.

......

36EE

4!._ .. ___28+------~-------:-----·"'
34

0.. .... ~......... ___

•

.,

Q.

42

•

•1 + '·~
Qa,.
•• o•~ ~70~...................

Q.

200

°'

•

~~ia.•A't, IJ. fh

• 00

E 32

:i

~ 34

..

c

•

26

38

40

42

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 23. T. truncatus. Measurement no. 2 Anterior
tip of tympanic bu!Ia to inner posterior prominence. For marks see Fig. 5.

Fig. 24. T. truncatus. Measurement no. 3 Tip ofsigmoid process to outer posterior prominence.
For marks see Fig. 5 .

..c56

..c66

°'
0

c
~54

"'~52

.6.ol/i

c

"'~50
rt

..

+

A. .AA

.<t
•

:

0 A

•

+

E
E

o"'

21

---~.-----2---------:,,..

A~--='~~----------~---~---~--~···_--_·,.J-,---"'--___J'--_.J.---1...J19
34

36

38

40

42

.•

...

°'
0

c
~62

0

AO

~58

--!

'b
+

nl

ca..

lab•

A

~

A

1.•

o•~

0

o

AA i

...

b

~·, ·.~.Q~+

A

A OQ

••

~
(i°" 0_______________ ...... ----------------·;··--

~ 54

"'

Q.

L--3~4_

E
E...........

24
21_c;___.36_ _,__~3~8-..___4~0:---'--4~2

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 25. T. truncatus. Measurement no. 4 Tip ofconical process to outer posterior prominence.
For marks see Fig. 5.

Fig. 26. T. truncatus. Measurement no. 5 Widthof tympanic bulla. For marks see Fig. 5.

and their proportional dimensions are shown in Figs. 5-20 and Table 5. Though
the length of periotic bone does not increase after the birth, that of tympanic bulla
increases about 6 mm in the adult than the new born animal. As the result, the ratioof the periotic bone to the tympanic bulla decreases with the growth of the animal.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

KASUYA

12

.c 58

.c 82
Ci
c
..!!! 78gi..!!! 54

0

0

E
E

~74

111

ca.

29

et

27

a.

E
E

ca.

21

&'.

19

g'50
~ 46

~ 70

34

36

38

40

34

42

36

38

40

42

Length of tympanic bulla in mm

Length of tympanic bufla in mm

Fig. 27. T. truncatus. Measurement no. 6 Heightof tympanic bulla. For marks see Fig. 5.

Fig. 28. T. truncatus. Measurement no. 7 Widthacross posterior prominences. For marks see
Fig. 5 .

.c

.c
&10
c
..!!!
0 16

gi16
..!!!

0 14
a.

Cl
111

E

E

~12

...

.

u

a.
a.10

_____________ ....................

34

36

38

6

-- ........ __ ....... ---40

5

42

a.

~

E
E

c:14
a.

7

~

a.
a.12

A A

-------- --- ------ -- ----- --;34

Length of tympanic bulla in mm

3638,,.,,.. - ................ ...

40

6

42

Length of tympanic bulla in mm

Fig. 29. T. truncatus. Measurement no. 8 Depth
of interprominential notch. For marks see Fig. 5.

Fig. 30. T. truncatus. Measurement no. 9 Widthof upper border of sigmoid process. For marks
see Fig. 5 .

.c

..

gi 8
..!!!

0 6
a.

Cl
111

ca. 4
u

Q;
Q.

E
E

E
E

2

------------34

36

38------40

2
42 1

6
5

34

36

38

40

42

Leng.th of tympanic butla in mm

Length of tympanic bulla in mm

Fig. 31. T. truncatus. Measurement no. 10 Widthof posterior branch of lower tympanic aperture.
For maeks see Fig. 5.

Fig. 32. T. truncatus. Measurement no. 11 Lengthof elliptical foramen. For marks see Fig. 5.

Tursiops truncatus
The tympano-periotic bones of 43 individuals caught in the Pacific coast ofJapan are used here. Among them the body length and sex are known on 38 inSci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

..

.c.
0.50
c

·2 90

~

"'a.E

E

E

~ 80
0

36
34
34

36

38

40

,._46
0

~42
<11
c
GI
~ 38
GI
a.

42

..

4

/J.

.t. A

Q &A

E

/J.

. .· ..

AO.&:-..........

16

0-~---·············:·:··~9...... .;----~-~---~

14

33

34

35

36

37

Fig. 34. T. truncatus. Measurement no. 14 Thickness of periotic. For marks see Fig. 5.

.c.
g. 8

•o

~

0

0 6

a. 64

Cl

GI
Cl
<11

• E

<U

~60
u

E

...Cll

33

~ 4

23
22

......................... 32

34

35

36

u

0

~ 2

2

...... ------------- ........ -----------------------

L-~_,_~.,,..,_~....,,..,~---=C:---";:'-;:;-.....O.,;;f;:;-~~ 1

37

32

33

34

35

36

37

Length of periotic in mm

Fig. 35. T. truncatus. Measurement no. 15 Widthof periotic. For marks see Fig. 5.

;

12

E
E

•

...

Length of periotic in mm

.c.

& 4

• E
- - · ~·~
8 A A c/ae4+ o
4............__ +411 ci

Length of periotic in mm

~68

a. 56

AO

32

Fig. 33. T. truncatus. Measurement no. 13 Lengthof periotic shown in percentage of measurement
no. I. For marks see Fig. 5 .

°'e'--~-'".:;;..~..L....~--'~~--'-~--''--~-'-~--'

Length of tympanic bulla in mm

.c.
c

13

Fig. 36. T. truncatus. Measurement no. 16 Fundus
of internal auditory meatus to ductus endolymphaticus. For marks see Fig. 5.

.c.
g.57

°'

~10

~

0 49
E
E

.................. -- ................ ___ ..

.. ......

43----------

4

32

33

34

35

36

37

GI
Cl

<U

c4t

•

• 0

0

0

•

•

~ - • 4 66. A. . . 4.t.
~\11..-4• ~•-L~~.._.....:....---.;:J; + 0 o
4A0 e+ 6.tg

o

GI

u

~33

••

•

•

A

A

6

A

A•

~· o •

A

16----------··-·---=---------··/·--·····
32

33

34

35

E
E

A•

36·

15

37

Length of periotic in mm

Length of periotic in mm

Fig. 37. T. truncatus. Measurement no. 17 Fundus
of internal auditory meatus to aquaeductus cochleae. For marks see Fig. 5.

Fig. 38. T. truncatus. Measurement no.18 Lengthof facet on posterior process of periotic. For
marks see Fig. 5.

dividuals. Though the morphological feature of tympano-periotic bone of thisspecies is the typical of Delphininae, it resembles that of Globicephala in the presenceof needle-shaped processes on the superior process of periotic of the adult, and in theSci. Rep. Whales Res; Inst.,
No. 25, 1973.

14

KASUYAdeveloped ventral keel of tympanic bulla.
The relation between body length and length of tympano-periotic bone areshown in Figs. 21 and 22. There is observed almost no increase of the length oftympanic bulla accompanied with the growth of the animal. This is different fromthe case of Globicephala, and will be related with the weak development of anterior
spine in Tursiops.
The average length of periotic shows the increase of only about 2 mm in the
body length range between 250 cm and 320 cm. But this growth is considered to be
negligible in the latter discussion. The ratio of periotic length to the length of tympanic bulla slightly decreases with the increase of the latter (Fig. 33).
As shown in Figs. 23-39 and Table 5, the proportional dimensions of tympanoperiotic bone are stable in most of measurements. But in the measurements nos .
.r::.

g.52
.!!
0 48
<II

E
E

OI
111

c44
<II

u

..............................

---- ----·-------------------

32

34&'. 40

33

35

36

37

Length of periotic in mm
Fig. 39. T. truncatus. Measurement no. 19 Diameterof cochlear portion. For marks see Fig. 5.
TABLE 5. CHANGE OF THE PROPORTION OF TYMPANO-PERIOTIC BONES,WITH THE INCREASE OF TYMPANO-PERIOTIC OR BODY LENGTH.
A INDICATES INCREASING TENDENCY, B STEADY, C DECREASING.
Measurements

G. macrorchyncha

T. truncatus

1

A

B
B

c
c
c
c
c
c

2
3
4
5
6

7
8
9

10
11
13
14
15
16
17

18
19

22

c

B
or B
B
B
B
B

c

B or
B

c

B
B
B
B
B
B
B

c

c

B
B

B
B
B
B or

c
c
c

c

c

N. phocaenoides

A
A
A or
A or
A or
B or
A or
A or
B
c or
B
B

B
B
B
A
B
B
B

c
c or B
c

B
B
A
B

c

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

15

E
E

E

E 32
c

.!: 32

~31

~31
oc

c

ca. 30

e

-30

i

~ 29

~~~
E29

~28

~28
111

a.

~

a.

a.

~

100

80

120

140

~

160

80

100

120
11.0
Body length in cm

Body length in cm

160

Fig. 40. Neophocaenaphocaenoides. Relation between
body length and length of tympanic bulla (measurement no. 1). For marks see Fig. 3 .

Fig. 41. N. phocaenoides. Relation between bodylength and length of periotic (measurement no.
13). For marks see Fig. 3.

..cllO
c.c
~106

:5 82

0
~102
C'IJ

0

ca.
u

&'.

OI

c

a.

+

: 80

..

++
+

·•

+

~···• • •
61-.4

+

98

___________ ..........
28

32.........

--

29

0

a.

E
E

30

30

g' 78

E
E

ca.

~ 76
a..

.. ..... ----- -------

31

28............ ................ -

25
23

29

30

31

Length of tympanic bulla in mm

Length of tympanic bul la in mm

Fig. 42. N. phocaenoides. Measurement no. 2 Anterior tip of tympanic to inner posterior prominence. For marks see Fig. 5.

Fig. 43. N. phocaenoides. Measurement no. 3 Tipof sigmoid process to outer posterior prominence.
For marks Fig. 5 .

..c 63
c.c

..c68

••
•

~61

••

•++

0

~57

it

c.

c
~64

•

+

E

E

~59
C'IJ

ca.

+

---------

19

+:

17

ca.

29

30

31

+

+ +

+

,,,,, ....... __________ ....o..--- ........
0

4...

+

E

E

19

,,,''

it

/

28

+6

a.

gi6o
~56

------ ----------- ---------

0

!·~t

0

28

17

/

29

30

31

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 44. N. phocaenoides. Measurement no. 4 Tipof conical process to outer posterior prominence.
For marks see Fig. 5.

Fig. 45. N.phocaenoides. Measurement no. 5 Width
oftympanic bulla. For marks see Fig. 5.

3, 4, 6, 15, and 19, the ratio decreases with the increase of the length of tympanic
bulla or that of periotic. This will indicate that the growth of inner posterior prominence and cochlear portion is not parallel with the increase of standard length.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

KASUYA

16..

..c: 94°'c.!! 90..c: 63

0~86+

ca.."'

28

29

30

A

&

°'

c
.!! 61

E
E

0

28

g>59

26

l:! 82
a..
a.

••

a..

l:!
57
a..
a.

•

+

-------- __:.. __ .,--------·
28

31

E

.

ca..

29

30

+

E

+

19
18

31

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 46. N. phoca.enoides. Measurement no. 6
Height of tympanic bulla. For marks see Fig. 5.

Fig. 47. N. phoca.enoides. Measurement no. 7
Width across posterior prominences. For marks
see Fig. 5 .

.

..c: 18'6>..c: 26+°'c.!! 24

c
~ 16

0

0

a..

a..

g'22

g'14

...

~.

r'+·

l:! 20a..
a.

l:! 12
~
28

29

30

+

O

A

A

E
E
7
'---'-~-'----''---'-~-'---''---'-~-'---'~6

28

31

.

+ +;11-:-+-+

cIll

cIll

•

+

29

30

31

Length of tympanic bulla in mm

Length of tympanic bulla in mm

Fig. 48. N. phoca.enoides. Measurement no. 8
Depth of interprominential notch. For marks
see Fig. 5.

Fig. 49. N. phocaenoides. Measurement no. 9
Width of upper border of sigmoid process. For
marks see Fig. 5.
.<=..c: 13c.!! 11°'A•
0ca.."'
v

Q;

a.

.!!
u

-~ 104

0

•
9
7

a.

+

0

Ill
Cl

g.108

+
+

.. ______
28--...... _..
29

,.,

E
+

A

-------30

EE:0 100

4
3

"' 96
"E

31

Length of tympanic bulla in mm
Fig. 50. N. phoca.enoides. Measurement no. 10
Width of posterior branch of lower tympanic
aperture. For marks see Fig. 5.

..

."'
~

"'

a.

------- ........... _.. ........

, -.----------.......... ..

A

,,.

28

29

30

E
E

30
29

31

Length of tympanic bulla in mm
Fig. 51. N. phoca.enoides. Measurement no. 13
Length of periotic shown in percentage of measurement no. I. For marks see Fig. 5.

Neophocaena phocaenoides
The tympano-periotic bone of this species shows the typical features of that of
Phocoenidae. In this chapter samples from 19 individuals, including 16 from theSci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

..

.c 34
c.c
a.
- 32
0

.c 68
c
.!! 64

°'

0

0

a.

~30
111

+•
+

ca.

~ 28

et

C160

++

E
E

• +

-------- ---------------------------------.;-·-----

i:+-.

29

30

to

-----

c111

••

o+

------.!..__...
••

A· - A --

QI

+ +

~

A

it~ 56+++++ +------------_____________________________...
AA--------

9~~~-='"=~_.____,..,,___._~..,.....,,~_.__~.____._~8

28

17

28

31

29

30

E
E
18

17

31

Length of periotic in mm

Length of periotic in mm

Fig. 52. N. phocaenoides. Measurement no. 14
Thickness of periotic. For marks see Fig. 5.

Fig. 53. N. phocaenoiaes. Measurement no. 15
Width of periotic. For marks see Fig. 5 .

.c 1
c

~

++ ~

~ 6 +-+-----,~--~·-~
A

E

.

E

+ ++

30

4

3

++
+

111

ca.
u

--------------- ---------------~-------t---""'-·-29

+• ++

A

.&

0

0

28

.

°' 8

.

+

+

4

~ ------------------------------------------------

31

E
E

28

29

30

3
2

31

Length of periotic in mm

Length of periotic in mm

Fig. 54. N. phocaenoides. Measurement no. 16
Fundus of internal auditory meatus to ductus
endolymphaticus. For marks see Fig. 5.

Fig. 55. N. phocaenoides. Measurement no. 17
Fundus of internal auditory meatus to aquaeductus cochleae. For marks see Fig. 5.

.c 50
c
.!!45

0

*

. , _ _•_•_o_.+ +

°'

/'

0
~40
111

.c 51

+

*

E
15

~ 35

13

Cll

a.

28

29

30

••

c

E

cCll

°'

31

.!!49

o

~

~·-...........o*+. . ._~47 ________.

~+

• •

cCll
i
+ _________ ,.___+ _~ 45 ---------------·············P.··-----

E

E

15

0

•

28

29

30

13

31

Length of periotic in mm

Length of periotic in mm

Fig. 56. N. phocaenoides. Measurement no. 18
Length of facet on posterior process of periotic.
For marks see Fig. 5.

Fig. 57. N.phocaenoides. Measurement no. 19 Diameter of cochlear portion. For marks see Fig. 5.

adjacent waters of Japan, are used.
As shown in Fig. 40, there is observed slight increase in the length of tympanic
bulla accompanied with the growth of the animal. The increase is about 2 mm
when the body length increases from 80 cm to 150 cm. The length of periotic bone
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

18

KASUYA

seems not to increase after birth (Fig. 41). As the result the ratio of the periotic
length to the tympanic length decreases with the increase of the latter (Fig. 51 ).
The relative growth of tympano-periotic bone is shown in Figs. 42-57 andTable 5. The proportional dimensions of the tympanic bulla are increasing or
stable in relation to the length of tympanic bulla. The posterior branch of lower
tympanic aperture (measurement no. 10), which is large in this species, decreases therelative width in the larger tympanic bulla (Fig. 50). The thickness ofperiotic bone(measurement no. 14) is nearly constant (Fig. 52). The length of the facet on posterior process of periotic is proportionally large in the larger periotic (Fig. 56).
This seems to be related with the fact that, in this species, the posterior process of
periotic is directed toward posterior direction, and the length of periotic is directly
influenced by this process.

1

2

3

4

Fig. 58. Contour of ventral view of tympanic bulla and of lateral view of periotic.
I, <:,iphius cavirostris. 2, Berardius bairdi. 3, Hyperoodon ampullatus. 4, Mesoplodon
ginkgodens.

MORPHOLOGY OF TYMPANO-PERIOTIC BONE
It is intended, in this chapter, to show the diagnostic characteristics of the tympanoperiotic bones of each species and taxa. The taxa used here is based on the classification considered from the morphology of tympano-periotic bone (Table 15).
The discussions on these morphological characteristics from the evolutional
point of view, or on the interrelationships of each taxa is made in the latter chapter.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

19

TYMPANO-PERIOTIC BONES

Physeteroidea
The most conspicuous feature of the tympano-periotic bones of this superfamily
is observed on the posterior process of tympanic bulla. It has large laminated orspongy element elongated and expanded distally, which is wedged between exoccipital and squamosal. Posterior process of periotic is usually sutured, not so
firmly, to the base of posterior process of tympanic bulla. Main part of accessory
ossicle is moved toward the tympanic cavity from the position between lateral wallof tympanic bulla and anterior process of periotic.
Sigmoid process is square or globular and large in size, cochlear portion inclines anteriorly.
Z,iphiidae
In the members of this family, the anterior part of the ventral wall of tympanic
bulla is cylindrical and is lacking in anterior spine. Involucrum is shorter than thelateral wall. Both posterior prominences are thick and short. Deep lateral furrowis prominent on the lateral wall of tympanic bulla. Sigmoid process is square andrather thin, and its lateral border is twisted posteriorly. Elliptical foramen ispresent.

2

3

Fig. 59. Contour of the lateral view of anterior process of periotic (top), and of
the dorsal view of posterior process of periotic. 1, Berardius bairdi. 2, .(iphiuscavirostris. 3, Mesoplodon ginkgodens.

On the periotic, anterior process, superior process, and posterior process arearranged, when seen from the dorsal, nearly on a straight line and the three parts
are clearly distinguished. Anterior process is shaped of triangular pyramid andhas a wide contact with the dorsal border of the lateral wall of tympanic bulla.
The posterior process is short, and flat at the distal end. Its facet for the posterior
process of tympanic bulla is almost smooth. Fundus of internal auditory meatus
is usually slender. Tractus spiralis foraminosus is separated by a developed septum
from the area containing foramen singulare and aperture of aquaeductus Fallopii.
There are two cases in the opening of foramen singulare, in one case it opens near
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

20

KASUYAaquaeductus Fallopii (,Z,iphius, Berardius, Hyperoodon), and in the other case it openes
near tractus spiralis foraminosus (Mesoplodon stejnegeri). The dorsal area of superior
process between fundus of internal auditory meatus and aperture of ductus endolymphaticus is highly protruded. Accessory ossicle is, different from that of Physeter,
small and does not entirely cover the anterior part of dorsal opening of tympanic
cavity.
1. ,Z,iphius cavirostris (PI. II)
As shown in Table 6, the size of tympano-periotic bone of this species is intermediate of Mesoplodon and Berardius.
The tympanic bulla is mote flat and its ventral wall is narrower than those of
Berardius. The rugose area on the ventral surface of tympanic bulla starts from interprominential notch and reaches the anterior margin of the bulla. The posterior
prominences, especially the inner, are small and interprominential notch is rudimental. There is formed a wedge-shaped protuberence at the postero-lateral tip ofouter posterior prominence (Fig. 58). The posterior branch of lower tympanic
aperture is narrower in this species than in Berardius bairdi and Mesoplodon spp.
(Table 6).
TABLE 6.

MEASUREMENTS OF TYMPANIC BULLA OF ZIPHIOID SPECIES.

Species
Sample sizeI.
5.

Standard length (mm)range
Width(%),
mean
7. W. across post. prom.
range
(o/o)
mean
10. W. post. branch ofrange
LTA (%),
mean
TABLE 7.

Sample size

15.

Width,

Berardius
bairdi6

Mesoplodon
stejnegeri
7

Mesoplodon
ginkgodens
251.8-59. 7
52.1-64.9
61.3

63.1-70.4
57 .1-67 .7
64.5

46.9-49.0
67.0-70.2
67.1

39.8-44 .1
69 .0-70 .4
69.7

38.6-50.2
41.6

52.6-57.0
54.5

48.2-55.8
50.8

51.0-64.6
57.8

3.8- 4.0
3.9

9.1- 9.6
9.3

7 .6-13.0
8.2

6.6

MEASUREMENTS OF PERIOTIC OF ZIPHIOID SPECIES (mm)Species

13. Standard length
14. Thickness,

Ziphiuscavirostris
7

range
mean
range
mean

Ziphiuscavirostris
7

Berardius
bairdi6

Mesoplodon
stejnegeri
4

Mesoplodon
ginkgodens
254.0-62.4
22.3-27.0
24.0
29.5-34.1
31. 7

66.9-75.8
29.0-38.1
32.9
34.7-37.2
36.4

44.3-50.9
16.4-18.3
17.8
26.9-29.1
27.7

41.0-42.3
20.4-20.6
20.5
22.3-23.1
22.7

Though the periotic resembles that of Berardius bairdi, it is distinguished by theshort and round anterior process and shorter posterior process (Fig. 59). There issometimes observed a transverse groove on the lateral surface of the base of anterior
process. But this occurs on some periotic bones of other Ziphioid species.
Sci. R.ep. Whales R.es. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

21

Berardius bairdi (Pl. III)The tympano-periotic bones of this species is the largest in this family(Table 6). The anterior part of the ventral wall of tympanic bulla is narrow andtriangular (Fig. 58). Both inner and outer posterior prominences swell well as in
the case of Mesoplodon.
Periotic is characteristic, other than the size, in the long and slender anterior
process, wider upper tympanic aperture, and slender and long posterior process.
On Berardius arnouxi (Pl. IV), only one sample from New Zealand was observed.
It was indistinguishable from B. bairdi.
3. Hyperoodon ampullatus (Pl. IV)
The length of tympano-periotic bone is nearly same with that of ,(,iphiuscavirostris. The tympanic bulla is cylindrical and the contour of anterior portion of
the ventral wall is not triangular, which condition is different from the case of
Berardius bairdi. Anterior margin of the ventral wall of tympanic bulla concavesslightly. Though outer posterior prominence is thick, interprominential notch isshallow as in the case of Z,iphius cavirostris (Fig. 58).
On the periotic, anterior process is shorter than Berardius but not so round asZ,iphius and Mesoplodon. The opening of fundus of internal auditory meatus isround and the margin of the openning provides a circular keel. The upper tympanic aperture is wide but shallow (Fig. 58).
4. Mesoplodon
The tympanic bulla of this genus is characterized by the thick posterior prominences and deep interprominential notch as those of Berardius, the flatness of thebulla, wide posterior branch of the lower tympanic aperture which is different fromthat of Z,iphius, and square-shaped ventral view oftympanic bulla. Posterior processof tympanic bulla is shorter and thicker than that of Berardius.
The surface of the periotic is smooth and the contour is roundish in general.
Anterior process is rather hemispherical than triangular pyramidal. Posterior
process is slender and not so strongly fan-shaped as Z,iphius. Upper tympanic aperture is smaller than those of other Ziphioid species. The size of tympano-periotic
bone is small.
Mesoplodon stejnegeri (Pl. IV). The ranges of the length of tympanic bulla andperiotic of seven individuals are between 46.9 mm and 49.0 mm, and 44.3 mm and50.9 mm respectively. These values are smaller than those of Berardius bairdi orZ,iphius cavirostris.
On the tympanic bulla the both posterior prominences and interprominential
notch develop well. The anterior extension of the latter opens on the lateral wall of
tympanic pulla encircling the anterior base of globular outer posterior prominence.
Ventral keel, originating at the anterior base of inner posterior prominence andpassing the inner side of the center of the ventral wall of tympanic bulla, reaches tothe anterior end ofinvolucrum. The rugose area on the ventral wall occupies wide
area between ventral keel and the lateral border of ventral wall (Fig. 60).
On the periotic, anterior process is slightly flat hemispherical with a small
conical protuberence on the anterior tip. Posterior process of periotic is slender2.

Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

KASUYA

22

than that of M. densirostris, M. carlhabbsi, and M. europaeus. Though there is a deep
furrow on the lateral surface of superior process, connecting the upper tympanic
aperture and base of cochlear portion, this is observed also on other Mesoplodon
species. The protuberence on the superior process is not developed. The canalfor stapedial musde is shallow.

, , ......
I
I

b
I

"

,,

, ,'

I

I
I

,'

&
Fig. 60. Contour of the ventral and lateral aspect of tympanic bulla of Mesoplodon.
Black line and dotted area indicate ventral keel and rugose area surrounding it.
1, Mesoplodon europaeus. 2, M. densirostris. 3, M. mirus. 4, M. ginkgodens. 5,
M. stejnegeri. 6, M. carlhubbsi.

Mesoplodon densirostris (Pl. V).

4 tympanic bullae and 1 periotic were studied.
Their size is slightly larger than those of other Mesopiodon species.
The ventral keel situates on the center, and the smooth area in the involucrum
side is wide, which feature is different from that of M. steJnegeri. As the innerposterior prominence is thin, the interprominential notch situates at the inner side.
Interprominential notch is shallow.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

23

The dorsal surface of periotic is smooth, and the lateral contour is arc shaped.
There is no furrow on the bases of anterior and posterior processes nor upper area ofupper tympanic aperture. The canal for stapedial muscle forms a deep crescentfurrow. Anterior process is of trigonal pyramid, and has a small conical protuberence on the anterior tip. Cochlear portion is flat, and pentagonal.
Mesoplodon europaeus (Pl. V). Tympanic bullae of 3 individuals and periotic ofan individual were studied. Their sizes are smaller than those of other species ofthis genus.
The tympanic bulla resembles that of M. steJnegeri in the situation of ventral
keel, and in the globular and protruding outer posterior prominence, but differs fromit in the thin inner posterior prominence which is similar to that of M. densirostris.
The most conspicuous feature of the periotic is the presence of a cylindricalprotuberence on the dorsal surface of superior process (Pl. V). Though the similar
structure is also observed on M. ginkgodens, M. europaeus can be distinguished from itby the shallower canal for stapedial muscle and the shape of cochlear portion inwhich the anterior and posterior margin is not in parallel. There is a verticalfurrow on the superior process near upper tympanic aperture.
Mesoplodon ginkgodens (Pl. VI). Tympano-periotic bones from two individuals
were studied. Its size is nearly same with that of M. europaeus. The flatness of
tympanic bulla is weaker than any species of Mesoplodon mentioned before. Outer
posterior prominence is very low and its apex is flat and oval in the contour. Inner
posterior prominence is higher but thinner than the outer. Prominent ventral keelsituates at the center of ventral wall of tympanic bulla and reaches the anterior tipof the bulla. The area inside of ventral keel is occupied by a wide smooth area
continuing to involucrum as in the case of M. densirostris. The rugose area isrestricted in the narrow part between ventral keel and lateral wall of tympanic
bulla (Fig. 60). The anterior part of interprominential notch is not smoothly
connected to the lateral wall.
Periotic resembles to that of M. europaeus. The base for stapedial muscle seems
to be wide and shallow as in the case of Ziphius cavirostris, but in M. europaeus it forms
a narrow furrow encircling the cochlear portion different from M. ginkgodens.
Cochlear portion is approximately square.
Mesoplodon mirus (Pl. III). Only one tympanic bulla was observed. The
ventral keel situates at the inner side of the center of ventral wall of the bulla as in thecase of M. steJnegeri and M. europaeus, but is characteristic in the strong elevation at
the anterior part of the keel. The smooth area inside of the ventral keel is wide
(Fig. 60). Outer posterior prominence is thick and high. Inner posterior prominence is small.
Mesoplodon carlhabbsi (Pl. VI). The size of tympano-periotic bone is nearly
similar to that of M. steJnegeri. On the tympanic bulla, the posterior prominences
especially the outer develops well. Interprominential notch is wide and smoothly
continues to the slope of lateral wall of tympanic bulla. Ventral keel continues
from the base of inner posterior prominence to the point near the anterior border ofthe bulla. It situates at the inner side of the center of ventral wall, and its highest
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

24

KASUYA

point at the middle of tympanic bulla. The smooth area on the inner side of ventral
keel is narrow (Fig. 60).
When seen from the cerebral side of periotic, the front border of anterior process, lateral border of superior process, and posterior border of posterior processcross in a right angle (Pl. VI Fig. 15 ). Anterior process is large and conical with the
apex on the cerebral side. Though there is a slight protuberence on the superior
process near the fund us of internal auditory meatus, it is not so conspicuous as thatof M. europaeus or M. ginkgodens. The cochlear portion, which contour is round,
has a wide fossa at the mesial side of the opening of fundus of internal auditory
meatus. The furrow of the base for stapedial muscle is wide and deep. The furrowon the lateral surface of superior process is shallow.

Physeteridae
This family includes only one species Physeter catodon. The tympano-periotic
bone of this species was precisely described by Yamada (1953). Several importantdiagnostic features of the ear bones of Physeter catodon (Pl. VII) are described below incomparison with other Physeteroidea species.

\ ~~~

~
1

PPT

2

~
3

Fig. 61. Schematic figure of the lower tympanic aperture of Physeteroidea. C,
Conical process. SP, Sigmoid process. PPT, Posterior process of tympanic bulla.
I, Ziphiidae. 2, Kogiidae. 3, Physeteridae.

The tympano-periotic bone of Physeter catodon is massive and the largest in
Physeteroidea. On the tympanic bulla, in spite of the strong development of involucrum and inner posterior prominence, outer posterior prominence and interprominential notch are greatly reduced. As the result of this modification, outer andinner posterior prominences and lateral border of sigmoid process situate nearly on
one plane (Pl. VII Fig. 5). Though the sigmoid process is thin and square as in thecase of Ziphiidae, the width ~s larger than the length. Its lateral margin is not
twisted posteriorly. Conical process and posterior branch of lower tympanic aperture are almost disappeared (Fig. 61 ). Accessory ossicle is large and roofs theanterior part of tympanic cavity. Posterior process of tympanic bulla is long andcomposed of thin laminated plates. In one example, a tympanic bulla of 59.3 mm
in standard length had the posterior process of 175 mm in length (Pl. VII Fig. 11 ).
The facet for the connection between posterior process of tympanic bulla and that ofperiotic has vague keels and grooves, and not so smooth as Ziphiidae and Kogiidae.
The tympanic bulla of Physeter differs in these features from those of Ziphiidae andKogiidae, but it resembles to that of Kogiidae in the U shaped anterior openning
Sci. Rep. Whales Res. Inst.,
Na. 25, 1973.

25

TYMPANO-PERIOTIC BONES

of tympanic bulla, swallen involucrum and its " 3 " shaped dorsal margin, absenceof lateral furrow, and in the closed elliptical foramen.
The superior process of periotic is massive, and continuous in structure withanterior and posterior processes. Anterior process is shaped of a curved slender rod.
Posterior process is cylindrical and tapered distally, which is connected to superior
process at a right angle and bent to downward. The posterior surface of posterior
process of periotic is rugose suggesting a sutural connection with squamosal. Aquaeductus Fallopii, foramen singulare, ductus endolymphaticus, and tractus spiralis
foraminosus opens in one openning of fundus of interal auditory meatus (Pl. VII
Fig. 9).

KogiidaeThis family is composed of two species in one genus Kogia. The diagnostic
features of the ear bones are as follows.
The size of tympanic bulla is one of the smallest among the toothed whales.
The smaller size is only found in Pontoporia blainvillei. The ventral wall of tympanic
bulla is flat and crosses with the lateral wall at a right angle, and there is observed nolateral compression of tympanic bulla nor deformation of posterior prominences.

1

2

Fig. 62. Schematic figure showing the difference of antero-lateral border of tympanic bulla, and of upper tympanic aperture between Kogia breviceps (!), andK. simus (2). Anterior direction is at the center.

Inner and outer posterior prominences developes well, and the latter protrudes posteriorly and the former postero-mesial direction at nearly a right angle with the latter.
Interprominential notch opens only posteriorly, and does not extend on the ventral
wall of tympanic bulla. As sigmoid process is not twisted, the anterior surface isexactly directed toward antero-posterior axis of tympanic bulla. The tip of sigmoid
process is spheric. The distal portion of posterior process of tympanic bulla isfunnel shaped. The facets for the connection between the two posterior processes
are smooth.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

26

KASUYAThe anterior process of periotic is flat and rectangular with the concaved
margins, which is different from other Physeteroidea species. On the thick superior
process, thin plate-like posterior process extends posteriory. Aquaeductus Fallopii
and ductus endolymphaticus opens outside of the opening of fundus of internal
auditory meatus inside of which foramen singulare opens.
Kogia simus and K. breviceps (Pl. VIII)
Though the ear bones of the two species is quite similar, they can be distinguished by several characteristics. On the tympanic bulla, the anterior margin of
the lateral wall is concaved in K. simus but is convex in K. breviceps. In this respect
the ear bone reported by Yamada (1953, Fig. 13) is classified into K. simus. On the
tympanic bulla of 3 K. simus, conical process is hidden inside of the sigmoid process
and cannot be observed from outside. But on one example of K. breviceps it is observed from outer side. This will probably be a specific difference. The upper
tympanic aperture is large in K. breviceps and small in K. simus (Fig. 62).

Platanistoidea
This superfamily includes the three families, Platanistidae, Iniidae, and Pontoporiidae. There are found some common features in the morphology of their ear
bones as mentioned below. On the tympanic bulla, the swollen base of outer
posterior prominence, the existance of median and lateral furrow, no lateral compression, and thick and square sigmoid process are common in Platanistoidea. On
the periotic, the opening of fundus of internal ausitory meatus is characteristic in
the roundness. The posterior processes of both tympanic bulla and periotic arevery small in size and the latter is bent downward.
TABLE 8.

MEASUREMENTS OF TYMPANO-PERIOTIC BONES OF PLATANISTOIDEA,SHOWN IN MM OR PERCENTAGE OF THE STANDARD LENGTH.
Species
Sample size

1.

5.
6.
13.
14.
15.
19.

Length of tympanic bulla (mm)Width of tympanic bulla (%)
Height of tympanic bulla (%)
Length of periotic (mm)Thichness of periotic (%)
Width of periotic (%)
Diameter of cochlear portion (%)
FIAM, Width/Length

P. gangetica

I. geoffrensis

7

5
38·2-45.6
60.3-70.3
74.0-81.4
25. 7-30.4
41.6-58.3
79.6-90.0
54.3-68.5
0.40-0.60

47 .1-63-5
44.3-54.4
61.3-74.8
33.4-42.3
23.9-35.9
55.3-66.5
38.3-44.8
o. 79-1.33

L. vexillifer P. blainvillei
I
I

47. I
51. 7
58.0
52.0
26.9
46.2
37.5
0.88

24.3
61.3
83.0
20.0
47.5
81.0
68.0
0.37

Platanistidae
This family includes only one species Platanista gangetica. The most conspicuous feature of the ear bone of this species is in the relation to the skull (seepage 48).
The anterior part of tympanic bulla is cylindrical and smoothly changes into
anterior spine, which length increases with the growth of animal. There is formed
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

27

small irregular needle-shaped processes in the median furrow, and gives the baseof ligament connecting the tympanic bulla and basioccipital. The lateral wall ishighly convex. The width of tympanic bulla is smaller than that of lnia geojfrensis(Table 8). This is related with the shape of involucrum. Sigmoid process, whichsituates at a right angle to the long axis of the bulla, is large in both thickness andwidth. Lateral furrow is weaker than that of lnia. The elliptical foramen opens,
but the shape is irregular. The facet for the posterior process of periotic has weaklongitudinal grooves and ridges.
Though the periotic is larger than that of lnia geojfrensis, cochlear portion issmaller than it in both thickness and diameter. The apex of cochlear portion
touches the involucrum. Round opening of fundus of internal auditory meatus issurrounded by a circular keel. The apertures of aquaeductus Fallopii and foramen
sigulare open at a close distance in the opening offundus of internal auditory meatus.
Anterior process is slender and curves along cochlear portion. At the dolsal base ofanterior process there is usually a small pillar shaped process directing towardcochlear portion (Pl. IX Figs. 8-10). As there is usually attached one or two ossicles on the anterior process, the shape of this part varies between individuals(Pl. IX Figs. 12-13). Accessory ossicle touches the anterior base of cochlear portion. Superior process is thin and is clearly separated by the grooves from theanterior and posterior processes. The antero-dorsal corner of the posterior processof periotic forms a nodular protuberence. A small rod shaped downward protuberence is on the posterior wall of upper tympanic aperture (Pl. IV Fig. 7), thisstructure strengthens the mechanical connection between posterior process of periotic and squamosal.

lniidaeThis family includes two genera lnia and Lipotes. One of the two features of
tympano-periotic bones distinguishing this family from other Platanistoidea is thatthe posterior processes of tympanic bulla and of periotic are not sutured to the skull.
And the other is the relatively strong sutural connection between both posterior
processes. The former structure is also observed in Pontoporia blainvillei, and thelatter in Platanista gangetica but the suture is stronger in lnia and Lipotes. Lateral
margin of sigmoid process is strongly convexed posteriorly. Elliptical foramen
opens.
1. Inia geoffrensis (Pl. X)
The ear bones of this species is smaller than those of Platanista and Lipotes. As
the involucrum expands to the inside, the width of tympanic bulla is large. Lateralfurrow is prominent. Median furrow is nallow and shallow, and situates at slightly
outer side of the center of tympanic bulla. The size of two posterior prominences
are nearly same, which is different from the case of Lipotes. The short posterior
process of tympanic bulla extends posteriorly. Its length is from 20.8% to 24.8%of the length of bulla.
On the periotic, the anterior and posterior processes are smaller in comparison with the size of cochlear portion, as in the case of Pontoporia blainvillei.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

28

KASUYA

Anterior process is square and short, but small process sometimes attaches on the tip.
The thickness (measurement no. 14) and breadth (no. 15) of periotic is larger thanthe corresponding values of Lipotes and Platanista (Table 8). The opening of fundus
of internal auditory meatus is usually round.
2. Lipotes vexillifer (Pl. X)
The length of tympanic bulla of this species is intermediate of Inia and Platanista, but that of periotic is larger than any of the two genera.
As involucrum of tympanic bulla does not expand to the inner side, the widthof tympanic bulla is smaller than that of Inia but resembles to that of Platanista(Table 8). The anterior part of tympanic bulla is conical and posseses no anterior
spine. Median furrow reaches to a shallow hollow near the anterior end of thebulla. Outer posterior prominence is large and spherical, but the innerposterior
prominence is thin. Ventral keel is low and narrow, and curves to the outer side at
the middle of the length. The diameter of cochlear portion is 19.2 mm, which isnearly same with that of Inia and larger than Platanista. But its ratio to periotic
length is far smaller than both of them. The opening of fund us of internal auditory
meatus is nearly round (14.5 mm xl3.5 mm) as in the case of Platanista. Anterior
process of periotic can be clearly distinguished from superior process, and its slendertip extends along the supero-lateral border oftympanic bulla. This feature is similar
to Platanista rather than Inia. Posterior process of periotic is also distinguished fromsuperior process as in the case of anterior process.

Pontoporiidae
This family includes only one species Pontoporia blainvillei (Pl. IX). Most
conspicuous feature of this family is the almost smooth articular facets on both posterior processes, but more perfect smoothness is found in Phocoenidae. Following
descriptions on the ear bones are for this species.
The tympano-periotic bone of this species is the smallest among the observed
Odontoceti. The ventral view of tympanic bulla is convexed laterally. Anterior
spine is absent. Median furrow developes well and is in parallel with the concaved
involucrum. Both posterior prominences are slightly large and nearly in same size.
It is a characteristic feature of this species that the lateral wall between base of outer
posterior prominence and the lateral furrow greatly swells. Lateral furrow is inconspicuous. Sigmoid process is square in the anterior view and its thickness islarge. Elliptical foramen is closed. The posterior branch of lower tympanic
aperture (measurement no. 10) is larger than any other species of Platanistoidea.
The posterior process of tympanic bulla and the tip of posterior process of periotic is
directed to the posterior.
The anterior process of periotic is short and pointed. The posterior and anterior
processes are continuous with superior process, which is similar to Inia and different
from Platanista and Lipotes. Cochlear portion is proportionally large as in the caseof lnia. This seems to have a relation with the shorter anterior and posterior
processes. The openings of aquaeductus cochleae and ductus endolymphaticus arewidely separated from the opening of fundus of internal auditory meatus.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

29

Delphinoidea
In this superfamily, the posterior process of tympanic bulla is relatively large,
and not sutured with the skull. Sigmoid process is small and thin, and L-shaped in
the lateral view. Lateral furrow is almost completely disappeared. Outer posterior prominence is round or flat, and projects postero-ventrally. Interprominential notch is deep. Elliptical foramen is closed in some species.
On the periotic, the anterior, posterior, and superior processes are continuous.
Accessory ossicle lies between anterior process and lateral wall of tympanic bulla,
separating the two parts. Anterior process is thick and square. Anterior marginof cochlear portion does not touch the anterior process.
This superfamily includes Delphinapteridae, Phocoenidae, Delphinidae, andMonodontidae.
Delphinapteridae
This family includes Delphinapterus leucas and Orcaella brevirostris. The common
features of tympano-periotic bones are as follows.
The outer and inner posterior prominences are developed well, and the width
across these prominences is large. The posterior branch oflower tympanic aperture
opens wide as in the case of Pontoporiidae and Phocoenidae. Elliptical foramen isFig. 63. Schematic figure of tympanic bulla and periotic of Delphinapterus leucas (1)and Orcaella brevirostris (2).
TABLE 9. WIDTH OF TYMPANIC BULLA SHOWN IN PERCENTAGE OF THE
LENGTH, IN ORCAELLA, DELPHINAPTERUS, AND MONODON.
Species
Sample size

0. brevirostris2

D. leucas
4

M. monoceros
4Range of the widthMean

52.0-57.5
54.8

58.0-59.0
58.9

37.5-41.4
39.6

closed. Bilateral compression of tympanic bulla is not occurred (Table 9, Fig. 63).
The posterior processes of tympanic bulla and of periotic are large and extend
straightly to the posterior direction. The suture between both posterior processes isrigid by the existence of deep ridges and grooves.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

30

KASUYA

Delphinapterus leucas (Pl. XI)
The anterior margin of tympanic bulla is lacking of anterior spine, and roundin the contour. Because of the low ventral keel and highly projected outer posterior
prominence, the ventral contour of tympanic bulla is saddle shaped when seen fromthe lateral side. Involucrum is strongly projecting to inner side. The tip ofposterior process of tympanic bulla is highly thickened.
The posterior process of periotic is thick and wide at the base, but thin at the
tip to form a wedge shape. On the dorsal surface of the posterior process there areirregular grooves (Fig. 63). Periotic of this species is sutured by this structure to thesquamosal (Pl. I Fig. 8, and Kleinenberg et al 1964). Superior process is thickand have a flat elevation higher than the opening of the fund us of internal auditory
meatus. The opening of the fundus of internal auditory meatus is surrounded by acircular crest. The opening of aquaeductus Fallopii is separated from foramen
singulare and tractus spiralis foraminosus by a developed crista transversa.
2. Orcaella brevirostris (Pl. XI)
The tympano-periotic bone of this species is nearly similar in size to that ofDelphinapterus leucas.
When seen from the lateral side the ventral contour of tympanic bulla is flat,
which is greatly different from D. leucas. The low ventral keel reaches slightly
beyond the midpoint of tympanic bulla. Shallow median furrow is formed along
the ventral keel. The outer posterior prominence, which is flat in D. leucas, iscylindrical in this species. The projection of involucrum to the inner side is observed on ZSI 274 in a same form as D. leucas, but weaker on USMN 199743. The
posterior process of tympanic bulla is larger than that of D. leucas in both thickness
and length, and possesses a large part of spongy structure.
The posterior process of periotic is also large and have a spongy structure. The
USNM specimen had larger posterior process than the ZSI specimen. Probably
this will be related with the age of the animal. Opening of ductus endolymphaticus
is surrounded by a large shallow funnel shaped area. Superior process is slenderthan that of D. leucas.
1.

Phocoeniaae
The diagnostic features of the tympano-periotic bones of this family are in the
direction of the posterior processes and in the smooth facets for the connection between both posterior processes. The former is similar to Delphinapteridae, but thelatter differs from it. The posterior process of tympanic bulla is large, but that ofthe periotic is smaller and shaped of a rod. The both posterior processes have nospongy structure (Fig. 64).
Other characteristics common in the tympanic bulla of this family are observedin the developed posterior prominences, deep interprominential notch, wide posterior
branch of lower tympanic aperture, existence of a vague median furrow reachingnearly anterior part of the bulla, absence of anterior spine, elevated anterior end of
the ventral wall, closed elliptical foramen, and in the absence oflateral compressionof tympanic bulla. But most of these characteristics are common to DelphiSci. Rep. Whales Res. Inst.,
No. 25, 1973.

31

TYMPANO-PERIOTIC BONES

napteridae.
The characteristic features of the periotic of this family are the linear arrangement of anterior, superior, and posterior processes, the triangular shape of cochlear
portion, and low crista transversa. The lengths of tympano-periotic bones are
small and approximately in the range between 27 mm and 34 mm.
1. Neophocaena phocaenoides (Pl. XII)The outer posterior prominence is cylindrical and far thicker than the innerposterior prominence. The posterior process of tympanic bulla is thick and spindleshaped in lateral view. Ventral keel is high as in the case of Phocoenoides. Posterior process of periotic is shaped of a slender rod with the pointed tip (Fig. 64).

880
~~~

&:~£d:. ~r~~~ ~\$-~~
3

Fig. 64. Schematic figure oftympano-periotic bones of Phocoenidae, ventral (top)and lateral view (middle) of tympanic bulla, and lateral and dorsal views ofposterior processes (bollom). PPP, Posteiior process of periotic. PPT, Posterior process of tympanic bulla. 1, Neophocaena phocaenoides. 2, Phocoenoides spp.
3, Phocoena phocoena.
TABLE 10. RANGE OF THE MEASUREMENTS OF TYMPANO-PERIOTIC BONES OF
PHOCOENIDAE, SHOWN BY THE PERCENTAGE OF THE STANDARD LENGTH.
Species
Sample size
Tympanic bulla
2. Tip to inner post. prom.
6. Height
Periotic
14. Thickness
19. Diameter of cochlear portion

N. phocaenoides

P. phocoena

Phocoenoides spp.

19

6

12

98.7-108.0
81.5- 94.3

89.3-97.9
75.2-87.3

89.2-97.2
67.9-82.5

26.6- 33.6
45.1- 51.4

32.6-39.0
38.9-44.6

35.8-39.4
37.5-43.5

This species differs from other two genera of Phocoenidae in the following measurements, or the distance from anterior tip of tympanic bulla to posterior end of innerposterior prominence (measurement no. 2), height of the bulla (no. 6), thickness of
periotic (no. 14), and diameter of cochlear portion (no. 19) (Tables 10 and 16).
2. Phocoena phocoena (PI. XII)The outer posterior prominence of the tympanic bulla is flat as in the case of
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

32

KASUYA

Phocoenoides. Ventral keel is low and most inconspicuous among the three genera of
Phocoenidae. The central area of the ventral wall of tympanic bulla is flat and is
not concaved as that of Neophocaena and Phocoenoides. The posterior process of
tympanic bulla is similar to that of Phocoenoides. The tip of posterior process of
periotic is robust as in the case of Phocoenoides, but it differs in the existance of a weak
constriction at the base.
The observation of each 3 specimens of Ph. phocoena phocoena and Ph. phocoena
vomerina could not find the difference between the two subspecies. One tympanoperiotic bone of Ph. sinus did not show any difference from Ph. phocoena.
3. Phocoenoides (Pl. XIII)
The shape of outer posterior prominence and of posterior process of tympanic
bulla differs from that of Neophocaena but resembles to Phocoena. The presence ofthe high ventral keel and the deep concavity at the middle area of ventral wallof the bulla differs from Phocoena. Though the periotic of Phocoenoides resembles
to that of Phocoena, it may be distinguished by the shape of the posterior process(Fig. 64).
There is found no morphological difference between the tympano-periotic boneof Ph. dalli and that of Ph. truei.
Delphinidae
One of the characteristic features of this family is found in the posterior processes of tympanic bulla and of periotic. The posterior processes project laterally
or postero-laterally, and their connection forms the suture with the longitudinalgrooves and ridges on the facets. But these features are observed also in Monodontidae. Other characteristics of this family are the larger or equal thickness ofouter posterior prominence in comparison with that of the inner, the narrow posterior branch oflower tympanic aperture, the low crista transversa, and aquaeductus
Fallopii openning in the same base with tractus spiralis foraminosus.
The presence of elliptical foramen, median furrow, and of anterior spine,height of ventral keel, and strength of lateral compression of tympanic bulla show
wide variation between taxa.
This family is divided, in this study, into 4 subfamilies or Sotaliinae, Delphininae, Orcininae, and Globicephalinae.
Sotaliinae
The characteristics of the tympanic bulla of this subfamily are the presence ofmedian furrow (Sotalia and Sousa) or similar longitudinal furrow (Cephalorhynchus),
swallen outer posterior prominence, weak ventral keel, usually closed ellipticalforamen, no lateral compression of the bulla, and absence of anterior spine.
On the periotic, there is no common characteristics except the slenderness ofthe superior process.
1. Sotalia spp. (Pl. XV)
Only two specimens from a S. guianensis and a S. fiuviatilis are measured. The
size of ear bone is nearly same with that of Stenella or Delphinus.
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

33

TYMPANO-PERIOTIC BONESThe anterior margin of ventral wall of tympanic bulla is nearly symmetricaland oval-shaped. Shallow median furrow, starting from the wide interprominential
notch, reaches near the anterior end of tympanic bulla. The rugose area on theventral surface of tympanic bulla is restricted to the inner side of median furrow.
Ventral keel is not so developed as Tursiops and Stenella. The inner posterior prominence is short and its tip does not project posteriorly beyond its posterior base.
This condition is not observed in Sousa and Cephalorhynchus. As the outer posterior
prominence, especially its anterior base swells well, the highest point is at the point
corresponding to the base of sigmoid process when seen from the lateral side. The
periotic is characteristic in the two longitudinal keels on the superior process (Fig.

Fig. 65. Schematic figure of tympano-periotic bones of Sotaliinae. Dotted area
indicates ventral keel, and the dotted line Median furrow or similar structure. 1,
Cephalorhynchus. 2, Sousa. 3, Sotalia.
TABLE 11. RANGE OF THE MEASUREMENT OF TYMPANO-PERIOTIC BONES OFSOTALIINAE, SHOWN BY THE PERCENTAGE OF THE STANDARD LENGTH.
Species
Sample size
Tympanic bulla
2. Tip to inner prost. prom.
5. Width
7. Width across post. prominences
10. Width of post. branch of LTA
Periotic
17. Aquaeductus cochleae to FIAM

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

Sotalia spp.
2

Sousa t.
1

Cephalorhynchus spp.
2

91.3-91.4
56.2-57 .3
48.6-49.4
5.4

97.4
57.3
54.1
7.3

89.2-90.9
57 .2-58.2
44.6-46.4
4.0

5.7- 6.8

5.4

17.9

34

KASUYA

65). According to the observation on several Sotalia specimen in Museo de Zoologia
de la Univ. de Sao Paulo, the opening of elliptical foramen is not rare.
There was observed no significant difference between S. guianensis and S .
.fiuviatilis.
2. Sousa teuszii (Pl. XIV)
Only one specimen from Senegal was studied. The size of ear bone is slightly
larger than that of Sotalia. The form of the anterior tip of tympanic bulla is, different from Sotalia and Cephalorhynchus, asymetric and outer margin projects laterally.
There is a clear median furrow along the outer base oflow ventral keel. Its width islargest at the middle of tympanic bulla. The lateral border of median furrow isbounded by a weak keel. The tip of inner posterior prominence projects posteriorly
beyond the base. The width across posterior prominences (measurement no. 7) isslightly larger than the other species of this subfamily (Table 11 ). Posterior processof tympanic bulla is square.
The superior process of periotic is slender and divided into lateral and dorsal
planes by a longitudinal keel (Fig. 65). The opening offundus of internal auditory
meatus is slender and separated from the triangular hollow surrounding the openingof ductus endolymphaticus by a keel on its lateral margin.
3. Cephalorhynchus spp. (Pl. XIV)
Only two individuals were studied. The size of ear bone is nearly same withthat of Stenella.
Anterior margin of the ventral wall of tympanic bulla is oval. The ventral
wall is elevated at the anterior part. The inner posterior prominence is thin andthe tip projects beyond the posterior base. lnterprominential notch opens wide.
The m.edian furrow like structure extend to the anterior margin of the bulla, but it
opens to the lateral wall of the bulla at its middle. The inner margin of involucrum
is straight. Posterior process is square.
The superior process of periotic has no prominent keel observed in Sousa andSotalia. The distance between aquaeductus cochleae and the opening of fundus ofinternal auditory meatus is markedly large (Table 11 ). Opening of fund us of internal auditory meatus is surrounded by irregular small processes.

Delphininae
Wide variation is observed in the morphology of tympanic bulla among themembers of this subfamily. The lengths of tympanic bulla and of periotic arefound between 28.0 mm and 41.5 mm, and 25.4 mm and 37.8 mm respectively. On
the tympanic bulla of this subfamily the bilateral compression is not occurred,
elliptical foramen is open, median furrow is absent, and inner posterior prominence
projects posteriorly beyond the base. The shape of ventral keel of tympanic bulla
can be used as the diagnostic characteristics of the genera. It is highest in Tursiops
and varies in the order of Tursiops, Stenella, Lissodelphis, Delphinus, Lagenorhynchus, andSteno. A low hemispheric prominence is present on the ventral wall of tympanic
bulla near the anterior end of involucrum (Fig. 66).
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

35

Tursiops truncatus in the Japanese waters (Pl. XVI)The taxonomical position of Tursiops in the coastal waters ofJapan is not fixed
yet. In this paper the name T. truncatus is tentatively applied for it after Ogawa(1938) and Rice and Scheffer ( 1968).
The ear bones of this species are the largest in the Delphininae. Ventral keel
develops high and reaches to the anterior margin of the bulla. Interprominential
notch is deep, and opens on the lateral wall of tympanic bulla in front of outer
posterior prominence. The both posterior prominences are nearly equal in the
thickness. In the ventral aspect of tympanic bulla the anterior margin is oval andsymmetrical (Fig. 66).
1.

Fig. 66. Schematic figure of tympano-periotic bones of Delphininae. Dotted area
indicates ventral keel, and dotted line the hemispheric protuberance. l, Steno.
2, Lagenorhynchus. 3, Delphinus. 4, Lissodelphis. 5, Tursiops.

On the periotic, it is characteristic that the posterior margin of the posterior
process is smoothly bent to the lateral direction. In other species of this subfamily
this part usually forms a clear angle. Fund us of internal auditory meatus opens at
the same level with superior process, where small needle-shaped processes are usuallyformed in the adult individual.
T. gill from the eastern Pacific and T. truncatus from the north Atlantic could
not be distinguished from Tursiops in the Japanese waters.
2. Stenella caeruleoalba (Pl. XVII)
Though ventral keel is high and straight as in the case of Tursiops, the tympanoperiotic bone of this species are far smaller. The inner posterior prominence isthinner than the outer, and the ventral view of the anterior margin oftympanic bulla
is not oval but possesses a short semicylindrical anterior spine. The antero-lateralpart of ventral wall of tympanic bulla slopes laterally, and shows a slight flatteningof the bulla.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

36

KASUYAOn the periotic of Stenella, the posterior process, anterior process, superior
process, and the opening of fund us of internal auditory meatus show wide individual
variation, and the identification of the species in this genus is difficult. But thepresence of an angle on the border between the dorsal and the posterior margins ofposterior process, of a flat area on the superior process which are present also insome Globicephalinae may be used as one of the characteristics of Stenella.
One tympano-periotic bone of presumably young Stenella styx from the northAtlantic was indistinguishable from that of young Stenella caeruleoalba.
( ?) Stenella roseiventris (Pl. XIX). This means the Hawaiian spinner dolphin.
The ventral keel of tympanic bulla is slightly lower than that of S. caeruleoalba, andscatters a irregular tubercles on it. Ventral keel is convexed to outer side. Its

2

3

4

5

Fig. 67. Schematic figure showing the variation of ventral keel in Stenella. Dotted
area indicates ventral keel. I is observed in S. caeruleoalba, 2 in S. attenuata andS. caeruleoalba, 3 in S. graffmani. 4 in S. longirostris, 5 in S. roseiventris. In thelast three species, 5ample is scarce to find the range of individual variation.

inside slopes to the involucrum (Fig. 67). Though this convexity is also observed on
Delphinus and S. longirostris, the length and width of ventral keel differ between
Delphinus and Stenella (Fig. 66). The swelling at the anterior end of ventral keel isoflong oval in the contour. The ventral view of the anterior margin of tympanic
bulla is of slender triangle with the anterior spine at slightly outer part (Fig. 67).
This species and S. longirostris show a common feature in the presence of a low keelon the outer border of ventral surface of tympanic bulla.
( ?) Stenella longirostris (Pl. XIX). This means the eastern Pacific spinner
dolphin, only two specimens are used here. Though the general feature of ventral
keel resembles that of S. roseiventris, its height is smaller and nearly same with that of
Lissodelphis. The hemispheric swelling at the anterior end of ventral keel was roundin the contour and higher than the ventral keel.
The flat area on the dorsal surface of superior process seems to be larger thanthat of S. roseiventris, but it may be in the range of individual variation.
Stenella attenuata (Pl. XVII). This is the spotted dolphins in the Pacific coast
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

37

ofJa pan. I hope to reserve the conclusion on the validity of several species of spotted
dolphins in the genus Stenella. The tympanic bulla and periotic bone of this species
resemble those of S. caeruleoalba, and the discrimination of tympano-periotic bone of
the two species is difficult. The ventral keel is conspicuously high. The roundprominence at the anterior end of ventral keel is flat and inseparable from ventral
keel.
Stenella graffmani (PI. XVIII) This species indicates the spotted dolphin distributing in the eastern Pacific. The tympanic bulla of this species closely resembles
that of S. attenuata. But the ventral keel seems to be slightly lower than that of S.
attenuata or of S. caeruleoalba (Fig. 67). The thickness of periotic (measurement
no. 14) is slightly smaller in this species than S. attenuata and S. caeruleoalba, but further confirmation will be necessary.
Stenella plagiodon This includes the spotted dolphin in the Atlantic. The
tympano-periotic bone resembles that of S. caeruleoalba and of other species of spotted
dolphins in the Pacific.
3. Lissodelphis borealis (PI. XX)
The size oftympano-periotic bone is similar to that of Stenella. On the surface
of ventral keel of tympanic bulla distributes a longitudinal fine reticular grooves.
Though the ventral keel is long and wide, its height is smaller than that of Stenella
spp. (Fig. 66). The hemispheric prominence at the anterior end of ventral keel
continues to low ventral keel. Inner posterior prominence is thinner than that ofStenella, Delphinus, and Tursiops, and its tip is pointed.
The periotic is characteristic in the flatness of the area surrounded by theposterior margin of the opening of fundus of internal auditory meatus, aperture ofductus endolymphaticus, and aperture of aquaeductus cochleae. The base for thestapedial muscle is concaved, and the aquaeductus cochleae opens on the same planewith the opening offundus of internal auditory meatus. The last feature is observed
also on Steno, but in other delphininae species it opens near the posterior wall ofcochlear portion (Pl. XX Figs. 4 and 10, and Text Fig. 66). Anterior process issquare and slender.
4. Delphinus bairdi (Pl. XX)
Banks and Brownell (1969) distinguished the Common dolphin in the eastern
Pacific into two species of D. bairdi and D. delphis, and showed the difference of thehabitat. According to my unpublished data, each one specimen from Formosa
and Kyushu in southern Japan have the feature of skull coinciding to D. bairdi.
Probably this D. bairdi distributes widely in the warmer warters in the North Pacific.
Present specimens includes this Formosa specimen. The Kyushu specimen wasused for reference.
The size of tympano-periotic bone is same with that of Stenella. The ventral
keel of tympanic bulla is so low as that of Lissodelphis and inconspicuous especially inthe anterior part, where only slender low keel continues to the base of the roundhemispheric protuberence at the antero-mesial corner of tympanic bulla (Fig. 66).
The inner area of this ventral keel, where fine tubercles are scattered, is wide andslopes to the involucrum. In the ventral view, the anterior border is more acuteSci. Rep. Whales Res. Inst.,
No. 25, 1973.

38

KASUYA

at the mesial side than the lateral side. The interprominential notch is wider than
Stenella and Lissodelphis, and the bottom is U shaped. A vague longitudinal keel ispresent along the middle line of ventral wall of tympanic bulla.
The aquaeductus cochleae opens on the posterior wall of cochlear portion as
in the case of Stenella.
Delphinus delphis (PI. XXI). The thickness of sigmoid process seems slightly
larger in this species than in the D. bairdi. Similar difference is also observed in thewidth of the head of sigmoid process (Table 12). Other features are same with D.
bairdi.
TABLE 12.

RANGE OF THE MEASUREMENT NO. 9, WIDTH OF UPPER
BORDER OF SIGMOID PROCESS, IN DELPHINUS.

Species
Sample size
Range in mm
Range in % of standard length
Mean in%D. bairdi
6

D. delphis
24.1- 5.0
13.2-15.2
14.4

4.8- 5.7
14.0-17.0
16.0

TABLE 13. RANGE OF THE MEASUREMENT NO. 7, WIDTH OF TYMPANIC
BULLA ACROSS POSTERIOR PROMINENCES, IN LAGENORHYNCHUS
SpecieSample size

Range in mm

Range in % ofstandard length

Mean in%L. obliquidens
L. acutus
L. albirostris
L. obscurusL. australis

1433

14.2-17.7
16.0-16.5
20.1-20. 5
16.5
15.5

42.0-49.4
48.0-49.6
54.2-56.0
49.2
47.4

45.5
49.0
54.9
49.2
47.4

Lagenorhynchus obliquidens (PI. XXI)
The length of tympano-periotic bone is intermediate of Tursiops and Delphinus.
The height and width of the ventral keel of tympanic bulla exceed those of Delphinus,
but it fades at or slightly beyond the middle of tympanic bulla. Two vague longitudinal keels are on the ventral surface of the bulla as in the case of Steno bredanensis(Figs. 66 and 68). In the ventral view of tympanic bulla the anterior margin isround and has inconspicuous anterior spine which situates slightly outer side. The
dorsal contour of the periotic is of arc, this feature is common to all species of Lagenorhynchus (PI. XXI Figs. 15 and 16).
Lagenorhynchus acutus (PI. XXII). A smooth area in the mesial side of ventral
keel is wide in this species (Pl. XXII Fig. 1). In the ventral view, the anterior
margin of the bulla is triangular and has an anterior spine.
Lagenorhynchus albirostris (PI. XXIII). Tympano-periotic bone of this species
is slightly larger than that of L: obliquidens.
As the both posterior prominences of tympanic bulla are thick and their tips
diverge, the width across the posterior prominences (measurement no. 7) is large(Table 13). Sigmoid process is peculiar in the posteriorly convexed lateral margin
5.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

39(Fig. 68). The ventral view of anterior part of tympanic bulla is strongly asymmetric.
In the lateral view of periotic, the contour of anterior process, superior process,and posterior process shapes of a arc. Though this feature is common in all Lagenorhynchi species, it is most conspicuous in this species.
Lagenorhynchus obsculus and L. australis (Pl. XXII). Observation is based on
only each one specimen. Though the anterior margin of the ventral view of tympanic bulla is symmetric in both species, the former differs in the presence of a shortanterior spine from the latter, in which it is round lacking in the anterior spine. The
sigmoid process is thicker in L. australis than in L. obsculus (Fig. 68).

2

3

4

5

Fig. 68. Schematic figure of the ventral view of tympanic bulla and of lateralview of sigmoid process of Lagenorhynchus. 1, L. australis. 2, L. obliquidens. 3,
L. albirostris. 4, L. obscurus. 5, L. acutus. For the dotted area and dotted line
see Fig. 66.

In L. obsculus, the interprominential notch is closed at the anterior base ofposterior prominences. Though the similar structure is also often observed in L.
obliquidens, it is more conspicuous in L. obsculus.
6. Steno bredanensis (Pl. XXIII)
The size of tympano-periotic bone is nearly same with that of Tursiops. The
ventral keel is developed both in the length and height, but it never reaches to theanterior tip (Fig. 66). The anterior half of ventral wall is cylindrical and presents a
deep groove at the antero-lateral border of ventral keel. The ventral view ofanterior margin of tympanic bulla is round lacking in the anterior spine. ThereSci. Rep. Whales Res. Inst.,
No. 25, 1973.

KASUYA

40

are observed two low longitudinal keels on the ventral wall of tympanic bulla, as in
the case of Lagenorhynchus.
The dorsal and posterior surfaces of posterior process of periotic cross at a rightangle. On the cochlear portion, the area posterior of the opening of fund us of internal auditory meatus is flat and wide. The aquaeductus cochleae opens in thisplane as in the case of Lissodelphis borealis (Fig. 66).

Orcininae
The tympanic bulla of this group is characteristic in the large size, atrophiedventral keel, no bilaternal compression, and cylindrical anterior portion. Inner
posterior prominence is long. Anterior spine is absent.
1. Pseudorca crassidens (Pl. XXIV)
The lengths of the tympanic bulla and periotic are m the range between
47.7 mm and 50.5 mm, and 42.8 mm and 49.0 mm respectively. The tympanic
bulla of this size with no trace of bilateral compression is found only in this species.

12

Fig. 69. Contour of the ventral view of tympanic bulla of Orcinus area (1) andthat of Pseudorca crassidens (2).

The ventral keel is slightly observed in the posterior half of the bulla. On the innerpart of anterior margin of the bulla, there are sometimes observed short needleshaped processes. The direction of posterior prominences is parallel or slightly
converging distally (Fig. 69). Interprominential notch is wide and U-shaped.
Though the elliptical foramen was present on all the 4 specimens, some were nearlyclosing.
The anterior process of periotic is straight and narrow. On the dorsal surfaceof superior process there is a long longitudinal keel. The area lateral of this keel
forms a wide flat area.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

41

Orcinus orca (Pls. XXIV and XXV)
The tympano-periotic bone of this species is the largest among the recent
Odontoceti. On the tympanic bulla, ventral keel is entirely disappeared and theventral surface is rugose with many scattered tubercles. The inner posterior prominence is smaller than the outer, and the two prominences diverge posteriorly at
the angle of about 45 °. The bottom of interprominential notch is narrow and Vshaped. Elliptical foramen is completely closed.
On the periotic bone, the superior and anterior processes are massive. In
comparizon with other parts of periotic, cochlear portion is small and its diameter(measurement no. 19) is only from 31.8% to 38.6% of the standard length ofperiotic.
Superior process protrudes higher than the opening of fundus of internal auditory
meatus, and on its dorsal surface short needle-shaped processes are present.
2.

Globicephalinae
The tympanic bulla of this subfamily is strongly flattened laterally. As theresult, the lateral and ventral walls cross at a shallow angle, and the distinction of thetwo parts is not clear. The ventral keel develops well. The inner posterior prominence is short, and its posterior tip does not project posteriorly beyond the base.
Anterior process develops in various degree. The frequency of the individuals
where elliptical foramen opens varies among the genera. The posterior branch oflower tympanic aperture is narrow.

fafJO /(D<) Pr< PD~

~~~~~

OQQ

W

0®~~~

G:)@8\2J~
~
1

2

3

4

Fig. 70. Schematic figure of tympano-periotic bones of Globicephalinae and Monodon. For the dotted area see Fig. 66. 1, Peponocephala electra. 2, Feresa attenuata.
3, Globicephala macrorhyncha. 4, Grampus griseus. 5, Monodon monoceros.

Usually there is a plateau-like flat area on the dorsal surface of superior processof periotic. In some cases needle-shaped processes are formed on this plateau.
The lengths of tympanic bulla and periotic were observed in the range from
34.0 mm to 52. l mm and from 30.8 mm to 45.2 mm respectively.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

42

KASUYA

Peponocephala electra (Pl. XXV)
The lateral compression of tympanic bulla is developed less strongly than other
Globicephalinae species (Table 17, Fig. 75). Elliptical foramen oftympanic bulla
was present on all 6 individuals studied. The outer slope of ventral keel does not
smoothly continue to the ventral surface of tympanic bulla, which condition is different from Feresa. The mesial contour of involucrum is straight.
The plateau on the dorsal surface of superior process is wide (Fig. 70), but inlesser degree than Grampus. No needle-shaped process is formed on the superior
process.
2. Feresa attenuata (Pl. XXVI)The tympano-periotic bone is larger in this species than Peponocephala. As themesial border of involucrum concaves and the outer posterior prominence is directed
to postero-mesial direction, the general contour of the ventral view of tympanic
bulla con vexes externally (Pl. XXVI Fig. 4 ). The involucrum is short. Anterior
spine is short and situates at the center of the bulla. The anterior part of the lateralwall is wide (Fig. 70, top). Similar feature is seen on the tympanic bulla of Grampus.
The lateral slope of ventral keel smoothly merges into the ventral surface of the bulla.
Elliptical foramen was open on the 2 among 7 individuals studied.
The characteristic features of periotic are in the relatively smaller cochlear
portion, narrow but thick anterior process, and in the straight contour of the dorsal
surface of anterior process and superior process (Fig. 70). The dorsal plane ofsuperior process, on which no needle-shaped process is formed, is not clearly separated from the lateral surface.
3. Globicephala macrorhyncha (Pl. XXVII)On the tympanic bulla of this species, the anterior spine situates slightly at the
inner side, and its length increases with the growth of animal. Inner posterior
prominence is shorter than the former two species. The lateral view of outer posterior prominence is more stumpy in Globicephala and Grampus than the former two
globicephalids. The height of ventral keel is lower at the middle of the length. The
outer slope of the ventral keel is not continuous to the ventral surface of tympanic
bulla. As the anterior part of the lateral wall of tympanic bulla is narrow, its
lateral view is triangular. Elliptical foramen was present, among 26 animals studied, on only one adult male of 431 cm in body length. The presence of this foramen is considered to be individual variation.
When seen from the lateral side, the dorsal contour of anterior, superior, andposterior process of periotic is round. Anterior process is thin. Superior process is
not wide. Needle-shaped processes are sometimes formed on the dorsal surface ofsuperior process.
The ear bone of Globicephala melaena (Pl. XXVII) was not distinguished fromthat of G. macrorhyncha.
4. Grampus griseus (Pl. XXVI)The tympanic bulla is characteristic, as G. macrorhyncha, in the strong flatness,
short inner posterior prominence, and stumpy outer posterior prominence. But it
differs from G. macrorhyncha in anteriorly expanded anterior border of lateral wall of
1.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

43

tympanic bulla, and the shape of ventral keel. In Grampus the ventral keel is not
low at the middle but shows the same height from the posterior end to the anterior.
But its height and width show wide individual variation. The outer slope of ventral
keel is not continuous to the ventral surface of the bulla. Anterior spine is on theanterior end of involucrum, but is lacking in rare case. Elliptical foramen was
found on one among 12 individual.
Periotic is massive. A conspicuous semicircular plateau project on the dorsal
surface of superior process. But on some individual, crowded needle-shaped processes conceal this plateau. Anterior process ofperiotic is short (Fig. 70).

M onodontidae
This family includes only one species Monodon monoceros. The following
description is for it (Pl. XVIII).
The tympano-periotic bone is larger than those of Globicephalinae. The
tympanic bulla is strongly flattened. Its width is only from 37.5% to 41.4% of the
tympanic length (Table 17, Fig. 75). Ventral keel is high and sigmoidal. Involucrum strongly increases the thickness near the anterior end. Inner posterior
prominence is thin and very short. Outer posterior prominence is long. Ellipticalforamen was closed on all observed specimens. Anterior spine is short. The widthof the posterior branch of lower tympanic aperture is wider than those of Globicephalinae (Table 14).
TABLE 14. RANGE AND MEAN OF THE MEASUREMENTS OF TYMPANOPERIOTIC BONES IN SOME DELPHINOIDEA SPECIES, SHOWNBY THE PERCENTAGE OF THE STANDARD IENGTH.
Measurement
Sample size

Species

Monodon monoceros
Globicephala macrorhyncha
Tursiops truncatus
Phocaenoides spp.
Delphinapterus leucas

No. 10No. 185.2- 9.7, 7.5
2.5- 5. 7, 3.8
2.2- 9.2, 4.5
7.7-12.6, 9.7
10. l-11.8, 10.8

51.3-68.4, 63.3
37.0-74.8, 48.5
35.1-52.8, 43.0
37.9-44.4, 40.7
44 .4-53 .0, 48.9

4
26
43
12
3

Measurement no. 10: Width of posterior branch of lower tympanic aperture.
Measurement no. 18 : Length of the facet on posterior process of periotic.

On the periotic, the opening of fundus of internal auditory meatus is surrounded by the thick needle-shaped processes. Crista transversa is inconspicuous.
The contour of the opening of fundus of internal auditory meatus shows wide individual variation, but it is usually round.
The long posterior processes of tympanic bulla and of periotic are firmly sutured and project laterally. Their lengths are nearly same.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

44

KASUYA

BIOMETRICAL BETWEEN-SPECIES SIMILARITY OF
TYMPANO-PERIOTIC BONESThe between-species similarity indices of tympano-periotic bones were calculated
from the 18 measurements and 4 morphological characteristics shown in Table 3.
As this is not to study the taxonomy of individuals but the systematic relationships ofspecies, species are used for the unit of discussion. As shown in Figs. 71 and 72, the29 species were compared. The numbers of individuals in one species are between
4 and 43 with the average of 9.1 individuals (Table 2).
t3 La. ob!iquidens
Similarity
11 D. bairdio - 20 .,.
24 St. attenuata
20 - 40• 99 20 St. caeruleoalba
40 - 60• 9 9 9 22 St. roseiventris•
60 - 80• 9 9 • 919 Lis. borealis
9 80 -100• 99 • • 918 Steno bredanensis•
100• • • • • ••25 T. truncatus• • • • • • • • 31 Orcinus orca• • • • • • • • 9 32 Peponocephala e.
• 99 • • 9 • • 9 9 30 Ps. crassidens• • • • • • • • • 99 33 Feresa attenuata• • • • • • • • • • 99 39 Monodon monoceros• • • • • • • • • • 999 38 Delphinapterus l.
• • • • • • • • • • • 9 • • 36 Grampus g.
• • • • • • • • • • 9 • • • 9 34 Gl. melaena• • • • • • • • • • • • • • • 9 35 Gl. macrorhyncha• • • • • • • • • • • • • • • •6 • 7 Ph. phocoena• • • • • • • • • • • • e • •9 Ph. dalli• • • • • • • • • • • • • • • • •10 Ph. truei• • • • • • • • • • • • • • • • • • • • 5 Neophocaena p.
• • • • • • • • • • • • • • • • • • • • • 50 Kogia breviceps• • • • • • • • • • • • • • • • • • • • •51 Kogia simus• • • • • • • • • • • •• • • • • • 52 Physeter c.
• • • • • • • • • • •• • • • • • • 40 Berardius b.
• • • • • • · • • • • • • ·• • • • • • • 9 49 Ziphius c.
• •• • • • • • • • • • • •• o • • • • • • • 43 M. stejnegeri• • • • • • • • • • • • • • • • • • • • • • • • • • t Platanista g.
• • • • • • • • • • • • • •• • • • • •• • • 2 lnia g.

r.-1•

Fig. 71. Matrix of similarity coefficient calculated from morphological measurement oftympano-periotic bones ofrecent toothed whales. On the scale, the upper
limits are not included in the range. The numbers coincides with those shownin Table 2. For other explanation see text.

In the calculation of the similarity indices, the standard lengths (measurement
nos. 1 and 13) were compared in the value shown in mm but other measurements were
calculated into the percentage of the standard length and then compared, because
it is not desirable to compare repeatedly the size of the tympano-periotic bone byusing the actual measurements. The 95% confidence limit of the mean value were
calculated in each measurement and species. Then the ranges were compared between the selected two species. The number of overlapped measurements shown by
the percentage of compared characteristics was used as the similarity index between
the two species. Same comparizon was made between each combination of thespecies. For the non-numerical characteristics, nos. 11, 12, 20, and 21, the calculaSci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

45

Delphinus bairdi
Stenella attenuata
Stenella caeruleoatba
lissodelphis borealis
Stenella roseiventris
lagenorhynchus obriquidens
Steno bredanensis
Tursiops gilli.---- Peponocephala electra~-- Orcinus orca
Monodon monoceros
Pseudorca crassidens
Feresa attenuata...___ Delphinapterus leucas
Grampus griseus
Globicephala melaena
Globicephala macrorhyncha
Phocoena phocoena & vomerina.....------+ Phocoenoides dalli
Phocoenoides truei. - - - - - - Neophocaena phocaenoides.....__ ___, Kogia breviceps
Kogia simus
Physeter catodon.----- Berardius bairdi...___ Ziphius cavirostris.___ _ _ _ Mesoplodon stejnegeri' - - - - - - - - - - Platanista gangetica
L...---------- lnia geoffrensis

30 40 50 60 70 80 90 100
Similarity
Fig. 72.

Species

Phenogram calculated from the matrix in Fig. 71. For explanation see text.

tion of the confidence limits was not made but compared in the similar manner mentioned above. This resut is shown by the matrix in Fig. 71. The phenogram shownin Fig. 72 was obtained from this matrix combining repeatedly the species of higher
similarity with the average linkage method (Sokal and Sneath 1963).
The result obtained here is influenced by the number of samples in each unit,
especially when the number of sample is small. And even when this result correctly
indicates the morphological resemblance of tympano-periotic bone, it is incorrect toconsider that it shows perfectly the phylogenetic relationships of the species, because
the compared organ is very limitted.
In Fig. 71, the species from Lagenorhynchus to Globicephala show a higher similarity, which are species included into Delphinoidea in this study. In the Delphinoidea, Delphinus, Lagenorhynchus, Stenella, Lissodelphis, Steno, and Tursiops show thehigher similarity than the other genera of Delphinoidea. The former group coinSci. Rep. Whales Res. Inst.,
No. 25, 1973.

46

KASUYAcides with Delphininae, but the latter includes not only Globicephalinae and Orcininae but also Monodon and Delphinapterus. This will mean that Globicephalinae,
Orcininae, Monodontidae, and Delphinapteridae can not be separated by the similarity index.
As shown in the matrix the tympano-periotic bone of Phocoenidae shows largemorphological distance from that of other members of Delphinoidea. And thephenogram in Fig. 72 shows the higher similarity between the genera of Phocoenidae
and Kogia. But as indicated in the latter chapter their tympano-periotic bones havea fundamental structural difference in the connection to the skull, and those of
Phocoenidae seems to be the very specialized of Delphinoidea type tympanoperiotic.
The low similarity between Platanista and lnia suggests their low phylogenetic
affinity. The species of Physeteridae and Ziphiidae show a low similarity to othertaxa.
EVOLUTION OF THE TYMPANO-PERIOTIC BONE

When the morphology of tympano-periotic bone is compared between the taxa of
toothed whales, there are found various kind of morphological pecuriorities which
are common to several taxa, show successive change from one taxon to another, or
can be lead from that of another taxon. These characteristics are considered to havebeen attained as the result of evolution of toothed whales. And their analysis will
reveal the process of specialization of tympano-periotic bone which have occurredin the history ofOdontocetL This chapter is to consider the process of the evolutionof some important morphological features of tympano-periotic bone of toothed
whales.

Interrelationships between tympanic bulla, periotic, and skull
In the land mammals the pars tympanic and pars petrosa, which correspond to
the tympanic bulla and periotic of Cetacea, are connected to squamosal and exoccipital by processus mastoideus, and form a part of cranial wall. But in thetoothed whales the tympano-periotic bone does not form a part of cranial wall. I
consider that the pars mastoidea or mastoid process is fused to tympanic bulla andcorresponds to the posterior process of tympanic bulla.
Fraser and Purves (1960, p. 77) classified the interrelationships between mastoid
process and skull into the following 3 types, or the type where all the element of
mastoid process is fused to tympanic bulla (Kogia), the type where all the element of
mastoid process is fused to squamosal (Platanista, Delphinoidea) and the intermediatetype where part of mastoid process is fused to tympanic bulla and the remaining tosquamosal (Physeter, Ziphiidae ).
But on my observation on Physeter catodon and other Physeteroid species, anotherinterpretation is possible. On the skull of smaller fetus of Physeter catodon (Pl. I
Fig. 1), mastoid process (posterior process of tympanic bulla) is imperfect, and the" mastoid element " of Fraser and Purves (1960) on the posterior region of squamosalSci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

Fig. 73. Tympano-periotic bones of toothed whales, arranged according to thedegree of specialization of the connection between tympanic bulla, periotic, andskull. Waved edge indicates suture or tight connection of bones, and dotted
area the laminated structure. A, Physeter. B, Ziphiidae. C, Kogia. D, Phocoenidae. E, Delphinoidea except D and F. F, Delphinapterus. G, Pontoporia. H,
Iniidae. I, Platanista. J and K, Hypothetical primitive toothed whale. BO,
Basioccipital. P, Periotic. PAR, Parietal. SQ, Squamosal. TB, Tympanicbull a.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

47

48

KASUYAis less developed and its structures is continuous to squamosal. The size andlaminated structure of this part becomes larger on 5.0 m newborn calf (Pl. I Fig. 2),
and finally .in the adult attains the similar laminated structure as that of posterior
process of tympanic bulla (Pl. I Fig. 3). The vague laminated structure is observedon the posterior region of squamosal even on Kogia and Ziphioid species which
posterior process scarcely shows the laminated structure (Pl. I Figs. 4 and 5).
Accordingly I consider that the posterior region of squamosal suturing to posterior
process of tympanic bulla have developed the similar laminated structure, in thetoothed whales, accompanied with the development of laminated structure on theposterior process of tympanic bulla. This hypothesis can explain more simply theevolution of the interconnection of tympanic bulla and skull.
Though there are observed, in the recent toothed whales, various patterns ofinterrelationship between tympano-periotic bone and the skull. They are continuous in some point of view, and can be classified into the following 7 patterns.

Platanista-type
This type is observed only in Platanista gangetica. It resembles Physeter-type but
differs in the posterior process of tympanic bulla.
The small posterior process of tympanic bulla is loosely sutured to squamosaland exoccipital with about 2/3 area of the distal lateral portion of the process. The
remaining inner proximal 1/3 area forms the loose suter with posterior process of
periotic (Pl. I Fig. 7). There is developed a fine laminated structure, as in the caseof Physeter, on the postero-ventral portion of squamosal to which the posterior process of tympanic bulla attaches. This laminated portion of squamosal is separated
by a slit extending from the postero-dorsal margin, and has a connection with themain part only at the antero-ventral part (Pl. I Fig. 6). The posterior process of
tympanic bulla is slightly seen on the surface of skull in the jevenile, but is hidden in
the adult. The dorsal and posterior surface of the posterior process of periotic
have a contact with the squamosal. One of the peculiar feature of this species is
the small conical process projecting from the postero-dorsal wall of upper tympanic
aperture. This process, posterior process of tympanic bulla, and squamosal interlock each other. As the result it is impossible to separate the three, without destroying one of them. This structure may have developed as the result of the specialization of Platanista.
The fossil Platanistid, Zarhachis flagellator (Kellogg 1924) belongs to this type.
It is supposed from its shape that the posterior process of periotic of some of Eurhinodelphinid species (Shi;:,odelphis sulcatus, Van Beneden and Gervaise 1868-1879) had
the connection with squamosal but not in another species (Eurhinodelphis longirostris,
Abell 1902). Anyway they differs from Platanista in the larger size of posterior
process of periotic.
Physeter-type
This type is found only in Physeter, and differs from the former type in thelarge and highly laminated posterior process of tympanic bulla and weaker connecSci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

49

tion of periotic and squamosal.
The long and strongly laminated posterior process of tympanic bulla is wedged
between squamosal and exoccipital. The postero-ventral portion of squamosal isalso strongly laminated, and to this part the posterior process of tympanic bulla
sutures. Though the suture is loose, it is impossible to separate the two part without
destroying some of the suture.
The posterior surface of posterior process of periotic is rugose suggesting acontact with squamosal. On the miocene Physeteroid species, the periotic bone of
Orycterocetus crocodilinus (Kellogg 1965) is supposed from the long posterior process
and the rugosity to have had a stronger connection with squamosal, but Aurophyseter
morricei in the same age (Kellogg 1931) had the smaller posterior process of periotic,
which suggest the probable variety of posterior process of periotic among Physeteroid
species.
There are observed longitudinal shallow grooves and ridges of the similar intensity as that of Platanista on the facets of posterior processes of tympanic bulla andof periotic, which does not form such a strong suture found on Delphinidae.

,(,iphius-type
This type is observed on all the Ziphioid species. The interrelationships between squamosal, exoccipital, and posterior process of tympanic bulla is same with
the Physeter-type. But this differs from it in the less developed laminated structure ofsquamosal and of the posterior process oftympanic bulla, in the separationofperiotic
and squamosal, and in the almost smooth facets on both posterior processes.
There is not observed such a highly laminated structure of squamosal and of
posterior process of tympanic bulla as found in Physeter, but the laminated structure
is restricted on their suturing surfaces. The posterior process of tympanic bulla isslender. This type is considered to be the intermediate of Physeter-type and Kogiatype.
Kogia-type
This is found on Kogia. The posterior process of tympanic bulla is short andthe distal end is widely expanded in a funnel shape. The laminated structure ofposterior process of tympanic bulla and of squamosal is restricted to the narrow areaon the surface of the skull (Pl. I Fig. 5). The facets on the both posterior processes
are perfectly smooth and forms no suture. Posterior process of periotic has nocontact with squamosal.
Delphinapterus-type
This type is represented by only one species Delphinapterus leucas. The posterior
process of periotic is firmly sutured with squamosal (Pl. I Fig. 8, Kleinenberg et al.
1964). On the removed periotic bones (AMNH 180017 and USNM 275075),
the dorsal surface of the posterior process of periotic has the irregular deep grooves
which are considered to help the connection between periotic and squamosal. But
this structure is not observed on the juvenile specimen (USNM 7356). The
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

50

KASUYA

connection between the posterior process of tympanic bulla and squamosal was notconfirmed. Other characteristics are same with the Delphinus-type.
Probably this type will retain the more primitiveness than the next Delphinus:.
type.

Delphinus-type
This type is represented by all the species of Iniidae and Delphinoidea except
those of Phocoenidae. The tympano-periotic bone looses the direct sutural connection with the surrounding elements of the skull, but is fixed with ligament in thecavity formed by basioccipital, exoccipital, and squamosal.
The posterior process of tympanic bulla is usually longer than that of periotic.
At the tip of the former there is a small spongy structure, which will probably be theremaining of the laminated or spongy structure found in the proceeding types. The
postero-ventral part of squamosal also retaines the small laminated structure. The
both posterior processes are, as mentioned by Yamada ( 1953 ), firmly sutured by thehelp of ridges and grooves on the facets.
Phocoena-type
This type is seen in Pontoporia and all the species of Phocoenidae. This is characterized by the absence of the spongy osseous tissue at the tip of posterior process of
tympanic bulla, and by the smooth or almost smoth facets of the posterior processesof tympano-periotic bone. Other features are same with the former Delphinus-type.
Relationships between the types
Fig. 73 shows the various types of the relation between tympanoperiotic boneand skull arranged in accordance with the degree of the specialization. This indicates that there are three main series of evolution in the tympano-periotic bone ofrecent toothed whales. The tendency of the degeneration ofsutural connection between tympanic bulla, periotic, and squamosal is observed in every three series. It
is also passible to say that the connection between skull and periotic through the
tympanic bulla is getting weaker. This specialization may have some relation withthe adaptation of acoustic systems into the water.
In the first series, or that of Physeteroidea, ·the posterior process of tympanic
bulla is not atrophied but attained the increase of the size, and in some species highspecialization of the structure of posterior process oftympanic bulla and of squamosalis observed. This does not necessarily mean the rigid connection between skull andtympano-periotic bone, but it is becoming weaker in the Physeteroidea series as in
the case of other series. Though the connection between the periotic and squamosalseems to be rather strong in Physeter catodon, the connection between squamosal andposterior process of tympanic bulla is not strong as the result of the development of
the laminated structures on the corresponding portion. And the connection between the both posterior process is also not strong. These are considered to haveproduced in some degree the weaker connection between skull and periotic throughthe posterior process of tympanic bulla. In Kogia, on the other hand, the structure
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

51

of posterior process of tympanic bulla and squamosal is not so specialized, but theconnection between the two parts, and that between both posterior processes havebecome very weak. These features suggest that the two genera of Physeteroidea, or
Kogia and Physeter have attained slightly different modes of specialization. Ziphiidae
shows the intermediate character of Pfryseter and Kogia in this point of view.
The second series, or the types found in Delphinoidea are considered to havederived from an ancestral type common with that of Physeteroidea, where the connection between skull and tympano-periotic bone was present. The both posterior
processes of tympanic bulla and of periotic are atrophied in size. And there areobserved various stages of specialization from the most primitive Delphinapterus tothe most specialized Phocoenidae. Probably the tympano-periotic bone of the mostof the species in the recent Delphinoidea may have attained the present condition, in
which it is usually separated from the skull, through the stage found in Delphinapterus
leucas.
The 3rd series is formed by the species of Platanistoidea. Though the ralation
between skull, tympanic bulla, and periotic of lnia, Lipotes, and Pontoporia belongs to
the Delphinus-type or to Phocoena-type, they should be separated from the 2nd series:
because of the stronger atrophy of the size of the posterior processes which is foundalso in Platanista, and of other morphological features common to Platanistoidea.
Among the 4 species of Platanistoidea, the relationships between tympanic bulla,
periotic, and skull is most specialized in Pontoporia and least in Platanista. As
Platanista has too highly specialized structure of squamosal, the ear bone of two otherfamilies can not be directly led from Platanista. The structure of ear bones of the two
families may have derived from a original type which is probably close to the earbone of primitive Platanista. There is expected hypothetical type which connects
the 2nd and 3rd series, where the decrease of the length of posterior process is started
but the connection between the two processes and squamosal is retained together
with the small part of laminated structure.
Platanista and Physeter, and in lesser degree all Physeteroidea species, retain theprimitiveness in having the connection between skull and tympano-periotic bone.
But their skulls show high specialization in the developed maxillary or premaxillarycrests. If these crests have the relation with the acoustics (Norris 1968), it may bepresumed that these species have developed a mechanism of hearing slightly different from other species.
As mentioned in the former chapter, the specialized posterior processes of
periotic and tympanic bulla observed in Phocoenidae and Pontoporiidae resemble
that of juvenile individuals of less specialized Delphinidae. This suggests that the
specialization occured on the posterior processes of tympanic bulla and of periotic of
Platanistoidea and Delphinoidea is one of the neoteny.

Sigmoid process and lateral furrow
The sigmoid process is a prominent plate projecting dorsally on the lateral wallof tympanic bulla and forming the anterior wall of lower tympanic aperture. This
process is observed in all the species of Cetacea, and shows the pecuriorities in eachSci. Rep. Whales Res. Inst.,
No. 25, 1973.

52

KASUYAtaxa. Lateral furrow is a groove found on the lateral wall of tympanic bulla infront of sigmoid process. Here is discussed the morphological variations and theinterrelationships.
In Physeteroidea the sigmoid process is square and the length of the dorsal
margin is not less than that of lateral margin. The lateral furrow varies among thethree families. In Ziphiidae, as the lateral margin of sigmoid process is twisted
posteriorly, its front surface is directed antero-laterally. The lateral margin is notlonger than the dorsal and the thickness is thin. The lateral furrow is deep andconspicuous. On the other hand, in Physeter, the lateral furrow is entirely disappeared. And the dorsal margin of sigmoid process is so long as 1. 7 times of thelateral, and the front surface is exactly directed to the anterior axis of tympanic bull a.
The thickness of sigmoid process of Physeter is thin as in the case of Ziphiidae. The
sigmoid process of Kogia is globular, but it is not twisted. As seen in Pl. VII Fig. 5
and Pl. VIII Figs. 2 and 17, the contour and direction of sigmoid process of Kogia
resembles those of Physeter.Lateral furrow is absent in Kogia.
Physeter

Kogia

Ziphiidae

Iniidae

Delphinidae

'O

c

"e

.,
.,c

.,
.,

'O

'O

""u

:c
la.

(/)

'O

.

!

'ji;
l-

a.

(/)

iii0

a.
a.

(/)

Platanista~
Pontoporia ~,<::­
.._o

~

.~

4-.
Sigmoid process: Square
Lateral furrow : Present

Fig. 74. Diagram showing the specialization of the sigmoid process (SP) and lateralfurrow (LF) in recent toothed whales.

Though Platanistoidea resembles Physeteroidea in the wide sigmoid process,its lateral margin is parallel to the lateral wall of tympanic bulla similar with that in
Delphinoidea. Lateral furrow is present in all species of Platanistoidea. In
Platanista the front surface of sigmoid process is placed to coincide with the anteroposterior direction of tympanic bulla, and the lateral margin and the dorsal margin
cross at a right angle. The sigmoid process of Pontoporia is similar with that of
Platanista, but the thickness is slightly larger. In both genera the lateral furrow isshallow. In two genera of Iniidae, Lipotes and Inia, the lateral margin of sigmoid
process is round and twisted to the posterior. This feature can be lead from that of
Platanista. The lateral furrow is deep.
The sigmoid process of the species in Delphinoidea coincides with that of
Platanista in important features, but differs from it in the smaller thickness and width.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

53

The lateral view is L-shaped. The lateral furrow is usually absent, but in somecases it remains vestigeally. These features are able to be lead from those of
Platanista by small modification.
In the fossile species, the sigmoid processes of Zvgorhyza kochii and Dorudon
osiris of Archaeoceti which may not be the direct ancestor of Odontoceti, are thin andsquare with long dorsal margin (Kellogg 1936) as that of Physeter catodon. The
lateral furrow was vaguely present on the both Archaeoceti species. But, of course,
it is not impossible to lead the sigmoid process of Mysticeti from that of Archaeoceti.
The tympanic bulla of upper miocene Odontoceti, Phocageneus venustus (Kellogg
1957) and Zarhachisflagellator (Kellogg 1924) resemble that of Platanista in the wide
and thick sigmoid process and in the presence of shallow lateral furrow. An
Eurphinodelphinid species Schizodelphis sulcatus has the sigmoid process similar tothat of Platanista, but it seems not to have retained the lateral furrow. The moderm
delphinid species Kentriodon pernix (Kellogg 1927) has the lateral furrow.
From the comparison of the sigmoid process of Odontoceti species described in
the above, the following consideration is possible. The sigmoid process of the three
species of platanistoidea can easily be led from that of Platanista gangetica, and eventhat of Delphinoidea from that of P. gangetica in another process.
The various shape of sigmoid process observed in Physeteroidea seems to haveoriginated from a common type which is square, flat, not twisted, and prepared alateral furrow in front of it. The sigmoid process of Platanista gangetica also able tobe led from this imaginative original type through the decrease of the width. Thisoriginal type may probably derived in Oligocene or earlier ages from some species of
Agorophiidae or Squalodontidae, on which sigmoid process I have no information.
Fig. 74 shows one of the most probable procedure which may have happenedin the process of evolution of sigmoid process and lateral furrow of tympanic bulla.

Elliptical foramen
The elliptical foramen (Yamada 1953) and vertical cleft of Archaeoceti andMysticeti (Kellogg 1936) are homologous. In the Mysticeti, by the absence of inner pedicle of tympanic bulla the vertical cleft forms a concavity connected to lower
tympanic aperture. But in Archaeoceti and Odontoceti, as posterior process of
tympanic bulla is connected by outer and inner pedicles to conical process and ininvolucrum respectively, vertical cleft is separated from lower tympanic aperture,and the elliptical foramen is formed.
In some taxa of recent Odontoceti, the elliptical foramen is closed or going to beclosed. This tendency seems to have happened independently in various small
taxa. Its featurs are as follows.
Physeteroidea
Elliptical foramen is perfectly disappeared in Physeteridae and Kogiidae. The
elliptical foramen exists in all species of Ziphiidae, but the opening is irregularly
shaped and sometimes narrowed by a thin plate of bone. This indicates that theelliptical foramen of Ziphiidae is on an earlier stage of the closure.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

54

KASUYA

Platanistoidea
In the two species of Iniidae the elliptical foramen opens round except one individual of lnia; On this individual of lnia geojfrensis (LACM 19588) ellipticalforamen opened only on the right side. In Platanista gangetica elliptical foramen waspresent on all individuals observed. But its opening is constricted by thin bone
tissue and it opens only through several small holes penetrating it. Probably theelliptical foramen of this species is also on the process of the closure. Ellipticalforamen is perfectly disappeared on Pontoporia blainvillei.
Delphinoidea
In all the species constituting Delphinapteridae and Phocoenidae ellipticalforamen is closed. In Delphinoidea its condition varies among the subfamilies.
The elliptical foramen is oval and its margin is thickened in all the species ofDelphininae. But the percentage of the opened elliptical foramen varies in thespecies of Globicephalinae. In Peponocephala electra it was present on all the 6animals studied, in Feresa attenuata on 2 individuals among 7 studied, in Globicephalamacrorhyncha on 1 among 26, in Grampus griseus on 3 among 12. This observationsuggests that Globicephalinae is a group of species where the closure of ellipticalforamen is progressing in various degree.
In Orcininae Pseudorca crassidens has the elliptical foramen opened, but it isclosed in Orcinus area. This indicates that tympanic bulla of Orcinus is more specialized than that of Pseudorca. Sousa teuszii, Sotalia spp., and Cephalorhynchus spp.,
which are included tentatively into Sotaliinae, usually have the elliptical foramen
entirely closed.
The elliptical foramen of Monodon monoceros, included into Monodontidae, wasopen on 1 individual among 4 animals studied.
Flatness, Ventral keel, and median furrow of tympanic bulla
The flatness of tympanic bulla mentioned below is the characteristics concerning the angle at which the lateral wall and ventral wall cross. This feature is prodused, in Delphinoidea, by the bilateral compression of tympanic bulla. On
primitive tympanic bulla the two walls crosses at nearly a right angle, but on somespecialized or flat one they cross at larger angle. The developement of ventral
keel and the disappearence of median furrow are observed often in accompaniedwith the progress of flattening.
The tympanic bullae of the two species of Archaeoceti mensioned in thechapter of " sigmoid process and lateral furrow ", and of three fossile Odontoceti
Phocageneus venustus, Zarhachis fiagellator, and Schizodelphis sulcatus have the ventral
wall crossing with the lateral wall at about 90° or slightly smaller angle, and the
median furrow extending anteriorly from the interprominential notch. And
ventral keel is not developed on these species. But in Kentriodon pernix, though thebilateral compression is not developed, the median furrow is almost disappeared
and ventral keel is developed.
These observations suggest that the primitive tympanic bulla shows no flattening
Sci. Rep. Whales Res. Inst.,
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TYMPANO-PERIOTIC BONES

55

and no development of ventral keel but possesses the median furrow, and that the
tympanic bulla of recent Odontoceti attained, starting from the primitive type,various combination of the specialization in median furrow, ventral keel, and thebilateral compression. Discussions on the process of these specialization are madebelow.

Physeteroidea
Median furrow is entirely lost in Physeteridae and Ziphiidae, but in two speciesof Kogiidae is retained the slight vestige of the furrow. On the tympanic bulla of
Kogia the ventral keel is not developed and the lateral and ventral walls cross at aright angle, which is one of the characteristics showing the primitiveness of the
tympanic bulla.
The dorsal part of the lateral wall of tympanic bulla is, in Ziphiidae, strongly
rolled into the inner direction, and the inner posterior prominence moved to thereverse. This modification is quite different from the usual bilateral compression
observed in other famillies of Odontoceti, but produces one of the flat feature of thebulla. This flatness is strongest in Ziphius in which the lateral wall and ventral wall
form nearly continuous arc, and gradually decreases in the order of Mesoplodon,
Berardius, and Hyperoodon. The ventral keel is inconspicuous in all Ziphioid species,and especially in Ziphius.
The tympanic bulla of Physeter catodon is cylindrical and shows a pecuriortransformation of the both posterior prominences (see page 23). This shape can be
led from the tympanic bulla of primitive Kogia as a result of the reduction of outer
posterior prominence and the movement of inner posterior prominence toward
the direction reverse of that occurred in Ziphiidae.
Platanistoidea
The tympanic bullae of the species of this superfamilly show no flattening.
Median furrow is observed in all species. The tympanic bullae of Platanista gangetica,
Inia geojfrensis and Lipotes vexillifer have common features in the weak ventral keel,swollen base of outer posterior prominence, and the conical anterior tip.
The general shape of the tympanic bulla of P. gangetica shows close resemblance
to that of the fossile species Phocageneus venustus, Shizodelphis sulcatus, and Zarhachis
ftagellator, except for the many needle-shaped processes in the ventral furrow of P.
gangetica.
The tympanic bulla of Pontoporia blainvillei slightly differs from that of other
Platanistoidea species in the slight development of ventral keel and the shape ofanterior tip.
Delphinoidea
In this superfamily, the flattening or bilateral compression of tympanic bulla
is well observed in the species included into Monodontidae and Globicephalinae.
The median furrow is found clearly only on some species included into Sotaliinae,
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

56

KASUYAbut ventral keel on various species of Delphinoidea. Further explanation is madebelow on each families or subfamilies.
In Delphinapterus leucas and Orcaella brevirostris, which constitute Delphinapteridae, the tympanic bulla is not flattened and ventral keel is low.
In Phocoenidae, rudimental median furrow is present in all species, andflattening is not observed. The ventral keel is not conspicuous in Phocoena, butdevelops well in Neophocaena and highest in Phocoenoides.
The tympanic bulla of Monodon monoceros shows the strong flatness and has
developed ventral keel. In these respect it looks like to situate at the extremity ofGlobicephalinae series (Fig. 75).
.1n1

Phn
f".PhdPon•:5 0.6

Nph

Sot

Tur

C•p~/La~
'1tb

Cl

c

.!

... ·~

StAfL1s Pep
el

-

Str

.r::.

Orb

Sic

"O

·~ 0.5

Gmc

-

\Gml
I
I

0

I
I

0

I

:;;

I

I

111

\I

a:

I

I
I

0.4

•Mon

20

30

40

50

60

70

Length of tympanic bul\a in mm
Fig. 75. Relation between mean length of tympanic bulla and mean ratio of thewidth to the length. Cep, Cephalorhynchus spp. Del, Delphinus bairdi. Dle, Delphinapterus leucas. Fer, Feresa attenuata. Gmc, Globicephala macrorhyncha. Gml,
Globicephala melaena. Grm, Grampus griseus. Ini, Inia geojfrensis. Lao, Lagenorhynchus obliquidens. Lip, Lipotes vexillijer. Lis, Lissodelphis borealis. Nph, Neophocaena phocaenoides. Mon, Monodon monoceros. Oro, Orcinus area. Orb, Orcaellabrevirostris. Pep, Peponocephala electra. Phd, Phocoenoides spp. Phn, Phocoena phocoena. Pit, Platanista gangetica. Pon, Pontoporia blainvillei. Psc, Pseudorca crassidens. Sot, Sotalia spp. Sou, Sousa teuszii. Sta, Stenella attenuata. Stb, Steno
bredanensis. Stc, Stenella caeruleoalba. Str, Stenella roseiventris. Tur, Tursiops truncatus(W. Pacific). Solid lines connect the members in a family or subfamily.

In Delphinidae, the morphology of tympanic bulla shows several characteristicfeatures in each subfamily or lesser taxa. In the three genera tentatively included
into Sotaliinae, the tympanic bulla is not flattened and ventral keel is slightly developed. Shallow median furrow is observed in Sotalia and Sousa, but inconspicous
in Cephalorhynchus. This is one of the primitive features of the tympanic bulla ofthese species.
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TYMPANO-PERIOTIC BONES

57

In Delphininae there is not observed the flattening of tympanic bulla nor median furrow. The genera of this subfamily is divided into two groups by the character of ventral keel. The first group includes Tursiops, Stene/la, and Lissodelphis.
Their ventral keel is long and reaches the anterior part of ventral wall of tympanic
bulla. Its height is largest in Tursiops and lowest in Lissodelphis. The second group
includes Delphinus, Lagenorhynchus, and Steno. In these genera the ventral keel does
not reach the anterior part, but disappears near the middle of tympanic bulla. As
the result the anterior part of tympanic bulla is cylindrical. Among the lattergroup the height of ventral keel is smallest in Delphinus and largest in Steno, but its
length is in the reverse. This characteristics is considered to be continuous between
the two genera situating at the extremities or Lissodelphis and Delphinus.
In Orcininae, the tympanic bulla shows no trace of flattening as in the case of
Sotaliinae and Delphininae. The median furrow is absent. Though the low
atrophied ventral keel is observed in Pseudorca in the posterior region of the tympanic bulla, it is almost entirely disappeared in Orcinus. These features resembles
the tympanic bulla of Delphinus and Lagenorhynchus, and can be led from them.
In Globicephalinae the ventral keel develops well and ventral furrow is absent.
The flattness is strong in all genera of this subfamily, but its degree varies between
the genera (Fig. 75).
The posterior process of periotic
As mentioned in the former chapter, the posterior process of periotic is considered to have had the connection with squamosal in the primitive form. In theseprimitive Odontoceti the posterior process of periotic is bent to ventral direction at

1

2

3

4

Fig. 76. Posterior view of tympano-periotic bone, showing the direction of theposterior processes. Lateral side is at the left. l, Peponocephala electra. 2, Monodon monoceros. 3, Platanista gangetica. 4, Orcaella brevirostris.

a right angle with the antero-posterior axis of superior process. The facet for posterior process of tympanic bulla is situated on its tip. In the recent Odontoceti,
this structure is observed on Physeter catodon and Platanista gangetica. I consider thatvarious types of posterior process of periotic of other Odontoceti may have derived
from the primitive type now found only in Physeter and Platanista.
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58

KASUYAIn other two families of Physeteroidea the direction of posterior process of
periotic is same with that of Physeter in principle. But the length is shorter, and the
distal tip is widened in Ziphiidae, or changed into thin plate in Kogiidae.
Though the posterior process in Iniidae and Pontoporiidae is continuous
to superior process and shorter than that of Platanista, the direction is similar to
Platanista. The atrophy of the posterior process is stronger in Pontoporiidae.
Platanista and Lipotes show the same feature where posterior process and superior
process of periotic are clearly distinguished externally.
The posterior process of periotic of Delphinoidea is thicker and longer thanthat of Platanistoidea. Its direction is classified into two types (Fig. 76). In one
type the posterior process is extended to the posterior in parallel with the axis ofsuperior process. All species ofDelphinapteridae and Phocoenidae are included inthis type. This type may have derived from the primitive type mentioned in theabove. In another type the posterior process is bent laterally or postero-laterally.
Delphinidae and Monodontidae are included in this type. Though it is not impossible to lead this type from the former, it may be more reasonable to lead directlyfrom the primitive type seen in Platanista or Physeter.
In the miocene Delphinids, Kentriodon pernix belongs to the latter type, but its
posterior process of tympanic bulla is directed posteriorly retaining the primitive
character. Delphinodon dividum (True 1912) belongs to the former type. The
posterior process of periotic of Lophocetus spp. (Kellogg 1955, Pl. 5-6) is extending
to the ventral and connection with squamosal is expected.
In Platanistoidea and Delphinoidea the direction of the posterior process of
tympanic bulla coincides with that of the periotic. But in Physeteroidea they do notnecessarily coincide because the posterior process of tympanic bulla is usually bent
at the distal part.

Anterior process of periotic
In all the species which have the primitive posterior process of periotic mentioned in the preceding chapter, or several species of Squalodontidae, Physeteridae,
and Platanistidae, the anterior process of periotic is shaped of a rod tapering at thetip. And this type of anterior process is found only on the species which haveprimitive posterior process of periotic or on its allied species. From these facts, it issuggested that the rod-shaped anterior process ofperiotic retains the primitive form,
and that the various forms found in the recent Odontoceti may have derived fromit. In this chapter the probable process of specialization of the anterior process of
periotic is discussed.
The anterior process of Berardius bairdi is most slender among the species ofZiphiidae and retains the most primitive feature, the trigonal pyramidal or hemispheric anterior process of other species of this family is considered to have originatedfrom this slender type seen in Berardius. The anterior process of periotic of Kogia
may have been formed through another process by loosing the length and thickness.
In Platanista gangetica, though the slenderness of the anterior process of periotic
shows the primitiveness, there are observed some specialization in usually observed
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TYMPANO-PERIOTIC BONES

59

small protuberence on the dorsal surface of the base of the anterior process (Pl. IX
Fig. 9). The anterior process of periotic of Lipotes vexillifer resembles that of Platanista in the curved and pointed shape, but its proportional length is shorter. In
Inia geojfrensis the length is shorter and the anterior margin is square, showing aslight resemblance to that of Delphinoidea. In Pontoporia blainvillei the process isstrongly shortened.
The anterior process of Delphinoidea is shaped of thick plate and anterior
margm 1s square. Its length is short. In the fossile species, the anterior process of
periotic of the miocene Kentriodon pernix (Kellogg 1927) and Delphinodon dividum(True 1912) had attained the feature similar to that ofrecent Delphinoidea.
Though that of Lophocetus spp. (Kellogg 1955) is also same, its posterior process of
periotic slightly differes from that of recent Delphinoidea.
CONCLUSION
The classification of recent toothed whales used in this report is shown in Table 15.
This classification is based mainly on the morphology of the tympano-periotic bone,paying the attention not to largely modify the classification generally have been
accepted. But the classification of Delphinoidea is slightly modified, affected by thewide variation of the morphology of the tympano-periotic bones.
This chapter considers the phylogenetic interrelationships of the taxa of recent
toothed whales based on the morphology of tympano-periotic bones.

Interrelationships among Archaeoceti, Mysticeti, and Odontoceti
According to the description of Kellogg (1936) and his photographs, the tympano-periotic bones of ,Zygorhiza kochii and Dorudon osiris show the following character.
The ventral wall of tympanic bulla is flat and wide, with which the lateral wallcrosses at a right angle. The inner border of ventral wall is straight. The anteriorborder of tympanic bulla or opening of Eustachian tube is partly closing and resembles that of Mysticeti than that of Odontoceti. Sigmoid process is square as in
the case of Physeter. Posterior process of tympanic bulla is fixed to tympanic bullawith the inner and outer pedicles, and here opens an elliptical foramen (verticalcleft) on the posterior wall of tympanic bulla. These features are similar with that of
Odontoceti. But the outer pedicle is reported to be smaller than the inner (Kellogg
1936). Though the both posterior prominences are prominent, the outer posterior
prominence is larger than the inner. lnterprominential notch is shallow, andmedian furrow is inconspicuous.
The periotic is sutured to squamosal and exoccipital at the anterior, superior
and posterior processes forming a part of cranial cavity as in the case of Mysticeti.
The long posterior process of periotic is wedged between squamosal and exoccipital,
and its tip reaches to the external surface of the skull. The ventral surface of theposterior process of periotic prepares longitudinal shallow grooves and keels to which
the posterior process of tympanic bulla sutures. Though the posterior process of
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60

KASUYAtympanic bulla is thinner than that ofperiotic, the lengths are nearly same. Judging
from the large width of the posterior process of tympanic bulla and the structure of
the corresponding part of squamosal (Kellogg 1936, Pls. 15, 20, 24, 25, and 28), I
consider that its anterior part may have sutured with squamosal as in the case ofrecent Physeteroidea and Platanista (Fig. 77).
In all the recent Mysticeti the involucrum of tympanic bulla is highly developed. There are found two types in the shape of posterior prominences. In all
the species other than Balaenidae, as the outer posterior prominence is strongly
atrophied or disappeared, the tympanic bulla is nearly hemispheric. But in Balaenidae outer and inner posterior prominences clearly exist, and the ventral side of
tympanic bulla is shaped of a flat square (Balaena) or of a triangle (Eubalaena).
Though in recent Mysticeti the interprominential notch is absent, the lsocetus sp.
from tertiary (Kellogg 1944) retains both the posterior prominences and interprominential notch. I consider that this condition is more primitive than that observedin recent Mysticeti. The sigmoid process is flat and shaped of a semicircular(Balaenidae) or of a triangle (other than Balaenidae). The tympanic bulla is connected to posterior process of tympanic bulla only by the inner pedicle, which is afeature entirely different from the condition in Archaeoceti and Odontoceti (Kellogg
1936).

Fig. 77. Skull of Archaeoceti showing the connection between ear bone andskull, drawn based on Kellogg 1936, PI. 15, Fig. 1, and PI. 25, Fig. 2. Dotted line
indicates the presumed area to which the posterior process of tympanic bulla was
sutured. 1, Zygorhyza kochii, ventral aspect. 2, Dorudon stromeri, posterior aspect.
BO, Basioccipital. EO, Exoccipital. OC, Occipital condyle. P, Periotic. PPP,
Posterior process of periotic. PPT, Posterior process of tympanic. SQ, Squamosal. T, Tympanic bulla.

As in the case of Archaeoceti, the periotic bone of Mysticeti forms a part of thebrain cavity, and the anterior and posterior processes are elongated in rod shape andthe latter is wedged between squamosal and exoccipital. Its distal tip nearly reaches
to the outer surface of the skull. Though Yamada (1953) showed another opinion,
it is clear on a fetus B. borealis (Pl. I Fig. 9) that the posterior process of Mysticeti is
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TYMPANO-PERIOTIC BONES

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TABLE 15. CLASSIFICATION OF RECENT TOOTHED WHALES BASEDON THE MORPHOLOGY OF TYMPANO-PERIOTIC BONES.
SuborderSuperfamily
FamilySubfamily
Genus
FamilySubfamily
Genus
FamilySubfamily
Genus
Superfamily
FamilySubfamily
Genus
FamilySubfamily
Genus
FamilySubfamily
Genus
Superfamily
FamilySubfamily
Genus
Subfamily
Genus
FamilySubfamily
Genus
FamilySubfamily
Genus
Subfamily
Genus
Subfamily
Genus
Subfamily
Genus
FamilySubfamily
Genus

Odontoceti
Physeteroidea
Physeteridae
Physeterinae
Physeter
Ziphiidae
Ziphiinae
Mesoplodon, Berardius, Tasmacetus, Z,iphius, Hyperoodon
Kogiidae
Kogiinae
Kogia
Platanistoidea
Platanistidae
Platanistinae
Platanista
lniidaelniinaeInia, Lipotes
Pontop.:iriidae
Pontoporiinae
Pontoporia
Delphinoidea
Delphinapteridae
Delphinapterinae
Delphinapterus
Orcaellinae
Orcaella
Phocoenidae
Phocoeninae
Phocoena, Neophacoena, Phocoenoides
Delphinidae
Sotaliinae
Sotalia, Sousa, Cephalorhynchus
Orcininae
Orcinus, Pseudorca
Delphininae
Steno, Lagenorhynchus, Delphiniis, Lissodelphis, Stenella, Tursiops
Globicephalinae
Peponocephala, Feresa, Globicephala, Grampus
Monodontidae
Monodontinae
Monodoncomposed of the elements of posterior process of tympanic bulla and of posterior
process of periotic. But the relative ratio of the two elements in adult individual is
not clear.
When the above features are compared with that of Platanista gangetica andPhyseter catodon which are considered to retain the primitive condition in the interSci. Rep. Whales Res. Inst.,
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KASUYA

relationships between skull and tympano-periotic bone, Archaeoceti has some common features both with Mysticeti and Odontoceti, but shows no perfect coincidence.
In order to lead the structure seen in Mysticeti from that of Archaeoceti, only thedisappearence of the outer pedicle oftympanic bulla which is smaller than the inner,and the fusion of the posterior process of tympanic bulla and that of periotic are thefundamental modification needed to Archaeoceti (Fig. 78). But to lead the earbone of some primitive Odontoceti, at first the periotic bone must be freed fromthe wall of cranial cavity and at secand the posterior process of periotic must greatly
degenerate to loose the strong connection with squamosal and exoccipital and toleave the sutural connection between the posterior process of tympanic bulla, squamosal, and exoccipital.

~\
A

B

~a
~B
' - -illcFig. 78. Schematic diagrams showing the connection between tympano-periotic
bone and skull. Waved edge indicates the tight connection or suture of bones, anddotted line the fused bone. A, Hypothetical primitive Odontoceti. B, Mysticeti.
C, Archaeoceti, in which the connection between squamosal and posterior processof tympanic bulla is not shown. For other marks see Fig. 73.

As the reduction of the outer pedicle of tympanic bulla had already started inArchaeoceti, I consider that it is easier to lead the ear bone of Mysticeti from that ofArchaeoceti than to do that of Odontoceti, which will suggest that Archaeoceti has
closer relationship with Mysticeti than with Odontoceti. This coincides with theconclusions obtained by Miller (1923) and Slijper (1946). But this does not necessarily mean that Mysticeti had originated from Archaeoceti.

Squalodontidae
According to Kellogg (1928) Squalodontidae is known in oligocene and miocene, and its primitive relative is in lower eocene. The description of the two
periotic bones of Squalodontidae is based on the drawings and photographs reported
by Kellogg (1923, 1931). No information on the tympanic bulla was obtained.
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On the periotic bone of Squalodon calvertensis, the anterior process and posterior
process are long and separated from the superior process by the grooves at the bases.
And when seen from the lateral side the dorsal borders of the anterior and posterior
processes cross at a right angle. The former feature resembles that of Platanista
and Lipotes, and the latter that of Physeter and many Ziphiids. As the posterior
process of periotic is slender at the tip and has the rugose area on the posterior surface, it is supposed that it had the similar connection with squamosal seen in Physetercatodon. The slenderness of the anterior process resembles both P. catodon and P.
gangetica. But the flat and low cochlear portion and slit-like opening of fundus ofinternal auditory meatus is peculiar.
On the other hand, the periotic bone of Squalodon errabundus has the swallen
anterior process resembling that of recent Ziphiidae. The large round cochlear
portion and the round opening of the fundus of internal auditory meatus are different from those of S. calvertensis but resemble that of Platanistidae and Physeteridae.
Anterior process is continuous to superior process. On the reffered specimen theposterior process was lost.
Above discussion shows that the periotic bone of Squalodontidae have many
characteristics common with that of Physeteroidea or Platanistoidea, though it issuggested that there exist some differentiation among the periotics of Squalodontidae.
As the conclusion it is suggested from the morphology of periotic that the recent
Odontoceti at least Physeteridae and Platanistidae had derived, as Squalodon, froma primitive Squalodon-like species.

Physeteroidea
One of the most conspicuous features of the tympano-periotic bone of Physeteroidea is the developed structure connecting it to skull. The similar but less developed
structure is found even in some species of Platanistidae, Delphinapteridae andEurhinodelphinidae. This suggest that, though there is found wide variation in themorphology of the tympano-periotic bone of recent Odontoceti, all of them havederived from one primitive type.
Though there are observed wide difference in the morphology of tympanoperiotic bones of the three families constituting the Physeteroidea, there is observedsome continuity in several features which permits the following discussion on theinterrelationships of these families.
When the tympano-periotic bones of the three families are compared, themorphology of the anterior and posterior processes of periotic, and the connection
between both posterior processes are most specialized in Kogia and least in Physeter.
But the laminated structure of posterior process of tympanic bulla is most developedin Physeter and less in Kogia and Ziphiidae. The arrangement of posterior prominences and the shape of sigmoid process show the most primitive condition in
Kogia, and the greatly modified in Physeter. But in Ziphiidae they have changed
the relative position in a way different from that occurred in Physeter. On this pointof view, the tympanic bullae of Physeteridae and of Ziphiidae seems to have been
specialized in different direction probably starting from the common original type.
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KASUYA

Accordingly it is considered that the three families had differentiated in the earlystage of history of Physeteroidea and the specializations of the anterior and posterior
processes of periotic and posterior process of tympanic bulla mentioned above might
have been attained as the result of evolution happened independently. The features of sigmoid process, lateral furrow, and elliptical foramen ofKogiidae resembles
more to those of Physeteridae than those of Ziphiidae. Though it is one of thepecuriority of the periotic ofrecent Physeter that the aquaeductus Fallopii and ductus
endolymphaticus open inside of the opening offundus of internal auditory meatus, inthe miocene Physeterid species Aurophyseter morricei (Kellogg 1931) and Orycterocetus
crocodilinus (Kellogg 1965) they open independently as in the case of recent Kogia.
These resemblances of tympano-periotic bone between Kogiidae and Physeteridae
will indicate the slightly closer phylogenetic relationships between Kogiidae andPhyseteridae. But it is of course sure that the phylogenetic distance between
Physeteridae and Kogiidae is not small as indicated by the difference of generalfeaturs oftympano-periotic bone, the process of telescoping of the skull (Miller 1923),
and by the condition of the fusion of the cervical vertebrae (Nishiwaki 1963, 1964).
Among several genera of Ziiphiidae, Berardius and Mesoplodon have well developed posterior prominences of tympanic bulla and interprominential notch.
But on the tympanic bulla of Ziphius, the outer posterior prominence has a wedgeshaped keel on its postero-lateral part, and both posterior prominences are thin.
Its interprominential notch is almost disappeared. In Tasmacetus, though the outer
posterior prominence retains the thick cylindrical form, there is observed the similar
keel found in Ziphius (Oliver 1937, Pl. III). Hyperoodon also resembles to Ziphius in
the atrophied inner posterior prominence and interprominential notch.
Based on these characteristics, the genera of Ziphiidae are divided into twogroups. One has less specialized tympanic bulla and includes Berardius andMesoplodon, the other has the more specialized and includes Ziphius, Tasmacetus andHyperoodon. The former is composed of the species which retain developed tootheven on the part of mandible other than anterior tip (with an exception of M.
mirus), and the latter only at the tip of mandible. Though the phylogenetic relarelationships among the species of Mesoplodon can not be presumed from the morphology of tympano-periotic bone, it should be noted that M. ginkgodens and Af.
europaeus show a common feature in the pecuriority of the superior process of periotic.

Platanistoidea
The tympano-periotic bones of this taxon show the common primitive featuresof unflattened tympanic bulla, existance of median and lateral furrows, large posterior prominences, and the shape of anterior, superior and posterior processes of
periotic, together with the specialized feature of the degenerated size of posterior
process.
As mentioned before the tympano-periotic bone of Platanista gangetica, which
retains the most primitive features among the recent species of this family, showssome resemblance to that of Physeter. Furthermore the arrangement of anterior andposterior processes of periotic and the constrictions at their bases suggest the probable
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

65

relationships to Squalodontidae.
The miocene Eurhynodelphinid species Schizodelphis sulcatus (Van Beneden andGervais 1868-1879) has the tympanic bulla highly resembling that of P. gangetica
except the existance of needle-shaped processes in the median furrow. Its periotic
bone also resembles that of P. gangetica in the shape of cochlear portion especially the
opening offundus of internal auditory meatus, and in the relationships with the skull.
But it greatly differs from P. gangetica in the larger size of the posterior process ofpenot1c. When the skull of S. sulcatus is compared with that of Platanista, the former
has larger brain case and weaker intertemporal constiction, and the proximal partof maxillae is expanded horizontally and covers the temporal fossa. As these features are similar to the modern Delphinoidea and different from Platanistoidea, it isunreasonable to lead Platanistoidea directly from the Eurhyodelphinids. Probably
the two taxa had originated from a same origin, and Platanistoidea attained thetendency to form the maxillary crest through the vertical extension of the lateral
margin of the proximal part of maxillae.
The tympano-periotic bone of a miocene Platanistoid species, /{,arhachis
flagelator (Kellogg 1924), is almost perfectly coincides with that of Platanista gangetica
except the needle-shaped processes in the median furrow of Platanista, but the
maxillary crest of -<,. flagelator is far smaller than that of P. gangetica. This suggeststhat Platanista did not gain large specialization of the tympano-periotic bone in theprocess of evolution, but did the strong modification on the maxillae and on thepterygoid (Miller 1923; Fraser and Purves 1960).
The tympano-periotic bone of lniidae is more specialized than that of Platanistidae in the degeneration of the connection with skull and in the shape of thesigmoid process, median furrow, and of the three processes ofperiotic. Between thetwo genera of Iniidae, Lipotes is considered to be more primitive in the form of the
tympano-periotic bone.
The strength of the development of the maxillary crest decreases in the order of
Platanista, /{,arhachis, Inia, and Lipotes. This order is rather reverse of the degree ofthe specialization of the tympano-periotic bones. This will indicate that the three
genera had been separeted at the very early stage of the evolution.
There have been reported two different consideration on the taxonomical position of Pontoporia blainvillei. The one considers Pontoporia close to Delphinoidea(Gray 1866; Kellogg 1928; Miller 1923), and the other to Platanistoidea (Flower
1867; Winge 1918; Fraser and Purves 1960: Nishiwaki 1963). Though the interrelationships between skull and tympano-periotic bone and the square-shaped
anterior border of the tympanic bulla are the very specialized features not observedin Platanistidae or in Iniidae, all the primitive features concerning the sigmoid
process, shape of outer posterior prominence, median furrow, unftattened tympanic
bulla, and round opening of fund us of internal auditory meatus are common to Platanistidae and Iniidae. and the specialized characteristics such as wide lower tympanic aperture can be led from the primitive condition found in Platanistidae andIniidae. As the conclusion, when based on the morphology of tympano-periotic
bone, Pontoporia blainvillei is considered to situate at the extremity of the specializaSci. Rep. Whales Res. Inst.,
No. 25, 1973.

66

KASUYAtion occurred in Platanistoidea. Furthermore the shape of anterior and posterior
processse of periotic resembles that of Inia, and the development of the vertical maxillary crest and the horizontal spreading of the proximal part of maxilla are intermediate of Inia and Lipotes. A tympanic bulla reportedly belonging to iniid species
Kampholophos serrulus (Rensberger 1969) is much similar, except the size, to that of
Pontoporia than Inia. They might suggest that Pontoporia is a relative of the Iniidae.
But Pontoporia should be separated from Iniidae considering the high specializationof the tympano-periotic bone.

Delphinoidea
The features of the tympano-periotic bones of this superfamily are described in
the preceeding chapters. As the relatives of this modern dolphins, Delphinodon
dividum (True 1912) and Kentriodon pernix (Kellogg 1927) are known from middle
miocene. Their tympano-periotic bones are, same as the features of the skull,
resembles to the recent Delphinoidea and differs from those of Eurhynodelphinidae.
But their tympanic bulla still retains the primitive features in the presence of medianfurrow, lateral furrow (no data on Delphinodon) and swallen inner posterior prominence.
Though, other miocene species Lophocetus spp. (Kellogg 1955) have the tympanic bulla and the anterior process of periotic resembling those of the former
Delphinodon and Kentriodon, its posterior process of periotic shows the primitivenesssuggesting the connection between posterior process of periotic and squamosal as
observed in recent Delphinapterus.
Though the tendency of the separation of the tympano-periotic bone and skull
is also observed in Platanistoidea it cannot be considered to be the direct ancestorof the Delphinoidea, because the strong reduction of the posterior process of periotic
is not observed in Delphinoidea. On the other hand the posterior process of periotic
bone of Shizodelphis sulcatus (Eurhynodelphinidae) is large enough to lead that ofrecent Delphinoidea. And its shape of the maxillae shows the similar specialization
to that of recent Delphinoidea. Accordingly it is reasonable to think that the recent
Delphinoidea had originated from a close ancestor of Eurhynodelphinidae. As
there had been established in the middle miocene both Eurhynodelphinid andDelphinid species (Kellogg 1928), it seems to be in lower miocene or earlier datewhen the primitive Delphinoids started.
In this study, the recent Delphinoidea is divided into Delphinapteridae,
Phocoenidae, Monodontidae, and Delphinidae. These four families are classified
into two groups by the shape and the direction of the posterior process of periotic.
One includes Delphinapteridae and Phocoenidae, and the other Delphinidae andMonodontidae.
The first two families seem to have derived from a common origin, in which
posterior extension of posterior process of periotic and possibly the tendency ofwidening of rostrum will be attained. I consider that this group constitutes one of
the three groups in Delphinoidea which have attained the wide rostrum. Other
two groups with wide rostrum are Orcininae and Globicephalinae. ThoughSci. Rep. Whales Res. Inst.,
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TYMPANO-PERIOTIC BONES

67

there is observed a strong resemblance between the two species constituting Delphinapteridae in the morphology of tympano-periotic bones, the sutural connection
between squamosal and periotic observed in Delphinapterus leucas will be a good reason to separate them into two subfamilies or Delphinapterinae and Orcaellinae.
Probably, after the differentiation from the stock common with that of Phocoenidae,
Delphinapterus and Orcaella might have differentiated in the arctic and tropicalwaters respectively.
In spite of the resemblance of the external appearance ofDelphinapteridae andGlobicephalinae, it is reasonable to consider that they are not in close relatives when
considered from the morphology of tympano-periotic bones. Because, other thanthe difference of the direction of the posterior processes, all the characteristic features of the tympanic bulla of Globicephalinae, or bilateral compression oftympanic
bulla, conspicuous ventral keel, anterior spine, short inner posterior prominence, andnarrow posterior branch of lower tympanic aperture lack in both Orcaella andDelphinapterus. Though Fraser and Purves (1960) found a resemblance of the air
sinus system between Orcaella and Orcinus-Globicephala group, the morphology oftympano-periotic bones of the three genera is quite different. Miller (1923) indicated the resemblance of the pterygoid among Orcaella, Monodon, and all species ofDelphinidae. But this will indicate only that the pterygoid of Delphinapterus isspecialized, and not the close phylogenetic relationships of Orcaella and Monodon toDelphinapteridae.
TABLE 16.

COMPARISON OF THE MORPHOLOGY OF TYMPANO-PERIOTIC
BONES IN PHOCOENIDAE

Genus
High ventral keel
WideLTA
Outer post. prominence
Post. proc. of tympanic bulla
Post. proc. ofperiotic
LTA:

Phocoena

Neophocaena

Phocoenoides

+
+

++
++

+++
++

Flat, Thick
Square, Thick
Thick

Cylindrical
ConicalSlenderFlat, Thin
Square, Thin
Thick

Lower tynipanic aperture

The tympano-periotic bone of Phocoenidae is characteristic in the direction andstructure of posterior processes of tympanic bulla and of periotic. The structure ofposterior processes is more specialized than that of Delphinapteridae. Similartendency of higher specialization of Phocoenidae is observed also in the degenerationof tooth and fusion of cervical vertebrae. Many other features of tympanic bulla
are common to those ofDelphinapteridae. Among the three genera of Phocoenidae
the tympano-periotic bone of Phocoena retains the most primitive features in all thecharacteristics compared, especially in the condition of the ventral keel, but the modeof specialization of outer posterior prominence, posterior process of tympanic bulla,
and of posterior process of periotic differ between Neophocaena and Phocoenoides. And
the tympanic bulla of the one genus cannot be led from that of the other. This will
suggest that these two genera have independently derived from a stock which is close
to Phocoena.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

68

KASUYAThe family Delphinidae contains most numerous and wide variety of species.
This group will have originated from a same stock with that ofDelphinapteridae andPhocoenidae, and attained the character in which the posterior process of periotic
extends to the lateral direction. There is a decreasing tendency in the width of theposterior branch of lower tympanic aperture. This family is divided into 4 subfamilies of Sotaliinae, Delphininae, Orcininae, and Globicephalinae based on themorphology of tympanic bulla.
Sotaliinae includes Sotalia, Sousa, and Cephalorhynchus. The closure of theirelliptical foramen indicates one of the specialization, but the existance of medianfurrow or similar structure, weak ventral keel, and no bilateral compression of tympanic bulla indicate the primitiveness. Their posterior branch of lower tympanic
aperture is wider than those of other 3 subfamilies. This feature is also considered
to be a primitive character, showing no extraordinary widened status found in
Pontoporiidae, Phocoenidae, and Delphinapteridae, nor the narrowed condition ofother subfamilies of Delphinidae. As this subfamily is established based on many
primitive features and modification of elliptical foramen which is very variable,
there remains a question on the phylogenetic uniformity of this group. Among thethree genera of this subfamily, Sotalia and Sousa show the higher resemblance in themorphology of tympano-periotic bone. Anyway the tympano-periotic bone of thesegenera shows higher resemblance to that of Delphininae.
The tympanic bulla of Delphininae is weakly specialized, and retains the mostprimitive condition in Delphinidae. This subfamily includes Steno, Lagenorhynchus,
Delphinus, Lissodelphis, Stene/la, and Tursiops. They are classified into two groups by
the feature of the ventral keel of tympanic bulla, the one includes the first three
genera and the other the last three. On the two genera at the boundary, Delphinus
and Lissodelphis, the height of ventral keel is the smallest, which will probably retain
the unspecialized original feature of the tympanic bulla ofDelphininae. In Fig. 78,
these two groups are shown in Delphinus group and Tursiops group. The genus
Stene/la includes many species which varidity is not established yet. When considered from the morphology of tympanic bulla, the North Pacific species S.
longirostris and S. roseiventris, and S. attenuata and S. grajfmani seems to be in close relations respectively. And S. caeruleoalba is in closer affinity with the latter pair of
species than the former.
Oricininae is constituted by Orcinus orca and Pseudorca crassidens. As their
tympanic bullae show the resemblance to those of Delphinus and Lagenorhynchus, thissubfamily seems to have derived from the stock which has such an unspecialized tympanic bulla. The tympano-periotic bone of Orcinus orca shows the higher specialization in the perfect disappearance of ventral keel, closure of elliptical foramen, andthe massiveness of anterior and superior process of periotic.
The two species included here in Orcininae have been often included in the
Globicephalinae here adopted. Though they resembles in the width of rostrum,
Orcininae greatly differs from Globicephalinae in the features of tympanic bulla
and periotic. In other characteristics of skull, Orcininae seems to have developed
the augmentation of tooth together with the decrease of tooth number. On theSci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

69

other hand, in Globicephalinae, the number of tooth seems to be decreasing withoutaccompanied by the much increase of size, and the function of the tooth in taking
the food is decreasing. Accordingly, I consider that the resemblance of the width of
the rostrum between Orcininae and Globicephalinae is not significant.
Globicephalinae includes Peponocephala, Feresa, Globicephala, and Grampus.
They are distinguished from other genera of Delphinidae by the morphology oftympanic bulla, especially by the bilateral compression, presence of anterior spineand ventral keel, and the closing tendency of elliptical foramen. In the least specialized species Peponocephala electra, the flatness of tympanic bulla is not strong and all
individuals retain the elliptical foramen open. This suggests that Globicephalinae
derived from a primitive Delphinidae which possessed such a tympanic bulla now
found in Delphininae, and diverged to wide variety of species.

TABLE 17.

COMPARISON OF THE MORPHOLOGY OF TYMPANO-PERIOTIC
BONES AND OTHER TAXONOMICAL CHARACTERS.

SpeciesMean
tympanic
width (%)

Openedellipticalforamen (%)*Rostrum
length/width*No. of
upper
tooth

*No. ofunitedcervicals

Peponocephala electra
Feresa attenuata
Globicephala macrorhyncha
Grampus griseus

55.3
53.5
49.8
50.1

100
28.6
3.8
8.3

1.83
1.58
1.16
1.04

21-25
8-11
6- 9
0

3
3-4
5-6
6

Monodon monoceros

39.6

25.0

1.31

0- I

0

Pseudorca crassidens
Orcinus area

60.6
56.1

100
0

1.49
1.36

8-11
10-13

6
4

Delphinapterus leucas
Orcaella brevirostris

58.9
54.9

0
0

1.50
1.10

8-10
15-17

0
2

Neophocaena phocaenoides
Phocoena phocoena
Phocoenoides spp.

64.4
62.3
62.3

0
0
0

1.03
1.39
1.47

15-19
23-27
23-27

5
6
7

* Refered from Nishiwaki (1963, '64), Nakajima and Nishiwaki (1965), Nishiwaki et al (1965), andKasuya (unpublished).

As shown in Table 17, there is observed a correlation between the strength of
specialization of tympanic bulla and that of other taxonomical characteristics ofGlobicephalinae. But this correlation can not be extended to other taxa of Delphinoidea. This will indicate that Globicephalinae should be separated from othertaxa which have wide rostrum. Among the species constituting Globicephalinae,
Peponocephala electra was indicated to have a strong resemblance to Delphinidae in themorphology of skull (True 1889; Nakajima and Nishiwaki 1965). And True
(1889) included this species into Lagenorhynchus. Though its tympanic bulla retains
the most primitive condition in the Globicephalinae species, it surely shows thetaxonomical characteristics of Globicephalinae and quite different from the tymSci. Rep. Whales Res. Inst.,
No. 25, 1973.

70

KASUYA

panic bulla of Lagenorhynchus. Accordingly Peponocephala should be included into
Glo bicephalinae.
The specialized features of tympanic bulla of Monodon monoceros are seen in thestrong bilateral compression, short inner posterior prominence, high ventral keel,

Mysticeti
Mesoplodon
Berardius
Tasmacetus-'""'""::::::c::::::::------ZiphiusHyperoodon
Kogia
Physeter"""---'~--------Platanista--...:::::::::=:::---__.:____ Lipotes
lnia
Pontoporia
Phocoenidae
L-.-:::.:::::::.-----Delphinapteridae
Orcininae
Delphinus group
Tursiops group
Sotaliinae
Globicephalinae
Mono don
EOCENE OLIGOCENE. MIOCENE PLIOCENE PLEISTOCENE RECENT

Fig. 79. Dendrogram of the recent Odontoceti considered from the morphology
of tympano-periotic bone. For other explanation see text.

and in sigmoidally curved inner margin of the involucrum. These characteristics
are not found in Delphinapterus leucas, but show higher resemblance to Globicephalinae, especially with Grampus. However, different from the general feature of
Globicephalinae, tympanic bulla of Monodon has no anterior spine and the compression of the bulla is stronger than any Globicephalinae species. The periotic of
Monodon shows specialization in the presence of thick and wide anterior process andpostero-laterally directed long posterior process of periotic. The former resembles
Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES

7I

more to Globicephala and Grampus than Delphinapterus, and the latter especially its
direction is quite different from Delphinapterus but is common to all Delphinidae.
On the other hand tympano-periotic bone of Monodon retains some primitive featuresof slightly wide posterior branch of lower tympanic aperture, round opening offundus of internal auditory meatus, and of elliptical foramen opened in higher frequency than in some Globicephalinae. But they are not of great importance intaxonomical point of view.
As the conclusion, though tympano-periotic bone of Monodon monoceros has someprimitive features not observed in Globicephalinae, most of features are considered
to be common to Globicephalinae or are the specialized form of it. This will suggest that M. monoceros and Globicephalinae derived from a common stock which had
started the specialization for Globicephala group, or the various modification of tympano-periotic bone, and the decrease in number of tooth, and increase in the widthof rostrum. The presence of a conspicuous tusk on the male Monodon is one of theextremity of the decrease of the tooth. But in this study Monodon is classified into
Monodontidae considering the slightly primitive features in the tympano-periotic .
bone and in the cervical vertebrae, and the specialized tooth.
In the past, Monodon was included in one group together with Delphinapterus(Winge 1918; Nishiwaki 1963), based mainly on the condition of the cervicals. But
the condition where all the 7 cervicals are separated is commonly observed in the
miocene dolphins, and it will not be necessarily correct to conclude the phylogenetic
relationships based on this kind of primitive characteristics.·
Fig. 79 shows the phylogenetic relationships of the recent toothed whales
presumed in the above discussions. Some fossile species refered in this study arealso shown in it. The geological age is based on Kellogg (1923) and adaptable
mainly to the fossile species.
SUMMARY

The tympano-periotic bone of toothed whales has attained the peculiar
morphological features and between species differences suggesting the probableefficiency as the taxonomical characteristics. This study intends, at first, to clarify
the morphology of tympano~periotic bones of recent toothed whales, and then to
discuss the phylogenetic relationships of the genera ofrecent Odontoceti based on the
tympano-periotic bones representing 313 individuals in 30 genera.
In the preliminary morphological study of the tympano-periotic bones, thefollowing results were obtained.
1. The bilateral difference of tympano-periotic bones between the both sides
of one individual was studied on 6 species of Delphinoidea. Though most of measurements showed no bilateral asymmetry, the asymmetry was expected in few
points. But it is small enough compared with the range of individual variation to
be neglected in the present study.
2. The growth oftympano-periotic bone accompanied with the growth of theanimal was studied on 3 species of Delphinoidea. The length of tympanic bulla
Sci. Rep. Whales Res. Inst.,
No. 25, 1973,

72

KASUYAshows slight increase after the birth, but the length of periotic does almost no increase. The proportional dimensions of tympanic bulla or of periotic vary in relation to their lengths and in species.
3. It is usually possible to identify the genus with hte morphology of tympanic
bulla or of periotic, but sometimes difficult to identify the species. The morphological characteristics of tympano-periotic bone for the identification of the species
or genus are described.
4. A similarity coefficient of the tympano-periotic bone was calculated basedon the 22 morphological characteristics. By this coefficient, Delphinidae, Phocoenidae, Kogiidae, Physeteridae, Ziphiidae, Platanistidae, and Iniidae are separated,
but Monodontidae and Delphinapteridae are not separated from Delphinidae.
The following results were obtained on the probable processes of the specialization of several morphological characteristics, through the comparizon of the tym~
pano-periotic bones of various taxa of recent toothed whales and fossil species.
1. In the primitive condition, the posterior process of tympanic bulla, posterior
process of periotic, and squamosal are considered to have been sutured each other.
But in the specialized species, these connections are disappearing in various degree.
2. The most primitive condition concerning the above characteristics is found,in the recent Odontoceti, on Physeter catodon and Platanista gangetica. But these
species show the higher specialization on the structure of the postero-ventral regionof squamosal where the posterior process of tympanic bulla sutures.
3. The degeneration of sutural connection between skull and tympanoperiotic bone is considered to have advanced independently in Physeteroidea,
Platanistoidea, and Delphinoidea. The suture between squamosal and posterior
process of tympanic bulla is retained in all species of Physeteroidea. In Platanistoidea and Delphinoidea the connection between squamosal and posterior process of
tympanic bulla is disappearing in various degree. Pontoporiidae and Phocoenidae
situate at the extremity where the suture is fully lost.
4. The primitive form of sigmoid process is considered to be of a thin square,
which is retained better in Physeter catodon. The form of sigmoid process foundwidely in Delphinoidea seems to have derived from this primitive type through thecondition of Platanista. The lateral furrow seems to have disappeared in several taxa.
5. The closure of elliptical foramen is considered to have occurred parallelly
in various taxa, and to be still progressing in some taxa. The elliptical foramen isperfectly retained in Delphininae.
6. In primitive tympanic bulla, the ventral wall and the lateral wall cross at aright angle. In Physeteridae, Ziphiidae, Monodontidae, and in Globicephalinae
their relation is modified. The median furrow is retained well in Platanistoidea,
but only slightly in Kogiidae, Delphinapteridae, Phocoenidae, and Sotaliinae.
7. There are observed two cases in the mode of specialization of ventral keel
which afford a base for the ligament connecting the tympanic bulla and basioccipital
crest, in one case it increases in height and in the other decreases.
8. In the primitive condition, the posterior process of periotic is directed topostero-ventral direction. This condition is observed in s.ome species of PhyseteroSci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

73

idea and Platanistoidea. In one of the specialized type it is directed to the posterior
direction, which is observed in Delphinapteridae and Phocoenidae. And in theother it is directed to postero-lateral or to lateral direction, which is observed in
Monodontidae and Delphinidae.
9. The anterior process of periotic seems to have changed from the primitiverod-shape which is observed in Physeter, Platanista, and Lipotes, to the triangularpyramid shape of Ziphiidae, to spool shape of Kogia, or to square shape of Delphinoidea, and lnia.
The following conclusions on the phylogenetic relationships of the taxa ofrecent Odontoceti were obtained from the consideration of the process of the evolution of tympano-periotic bone.
·
1. The fundamental structure of tympano-periotic bones of Archaeoceti
coincides neither with that of Mysticeti nor that of Odontoceti, but it shows higher
resemblance with the former.
2. The recent Odontoceti is considered to have derived from a primitive
Squalodon group, and classified into two groups. One is Physeteroidae, and theother includes Platanistoidea and Delphinoidea.
3. The group of Physeteroidea retains the suture between squamosal andposterior process of tympanic bulla, and shows a conspicuous specialization of theseparts. In its early stage of evolution, Kogiidae, Ziphiidae, and Physeteridae seems
to have been separated.
4. The recent Ziphiidae is classified by tympanic bulla into two groups, one
indludes Berardius and Mesoplodon, and the other ,Ziphius, Hyperoodon, and Tasmacetus.
5. The 2nd group of recent Odontoceti shows the tendency of the separationof tympano-periotic bone from the skull, accompanied with the degeneration ofposterior processes of tympanic bulla and of periotic. This group is devided into
Platanistoidea and Delphinoidea, which are presumed to have derived from a common origin.
6. In Platanistoidea, the regression of the size of posterior processes is stronger
but retains many primitive features of tympano-periotic bones than those of Delphinoidea. The differentiation of Platanistidae, Iniidae, and Pontoporiidae seems
to have occurred in the early period of evolution of Platanistoidea.
7. Delphinoidea is composed of the two groups. One includes Delphinapteridea and Phocoenidae, and the other Delphinidae and Monodontidae. These twogroups in Delphinoidea had originated from a common stock.
8. Delphinidae is composed of Sotaliinae, Delphininae, Oricininae, andGlobicephalinae.
9. It is presumed from the morphology of tympanic bulla that Orcininae
may have derived from a stock which is close to that of Delphinus or Lagenorhynchus.
10. Globicephalinae and Monodontidae show some resemblance in themo·phology of tympano-periotic bone.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

74

KASUYAACKNOWLEDGMENTS
Greatest thanks are due to the persons, institutes, and museums shown in Table I
who kindly offered the privilege to study their specimens.
Prof. M. Nishiwaki of the Ocean Research Institute, University of Tokyo,
collected the specimens for my study in Formosa, and read the draft and gave valuable suggestions. Dr. T. Tobayama of the Kamogawa Sea World offered many
specimens of Tursiops, Dr. D. Giraud-Sauveur of the Laboratoire de Phisiologie
Acoustique the specimens of the north Atlantic species, and Dr. W. A. Walker of the
Marineland of the Pacific the specimens of Stenella in the eastern Pacific. Dr. T.
Kamiya of the Faculty of Medical Science, University of Tokyo, and Dr. Y. Imaizumi of the National Science Museum offered valuable suggestions. This study wastechnically assisted by Miss. K. Nagayama, Mr. K. Haseyama, Mr. K. Kureha,and Miss. M. Kamata.
These persons are deeply acknowledged.
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Mem. Mus. Hist. Nat. Belgique, 2: 105-188.
BANKS, R. C. and R. L. BROWNELL, 1969. Taxonomy of the common dolphin of the eastern Pacific Ocean.
J. Mamm., 50 (2): 262-271.
BEDDARD, F. E., 1900. A book of whales. G. P. Putnam's Sons, London. 320 p.
FLOWER, W.R. 1869. Description of the skeleton of Inia ggoffrensis and the skull of Pontoporia blainvilli withremarks on the systematic position of these animals in the Order Cetacea. Trans. :(,ool. Soc. London, 6:
87-116, pls. 4.
FRASER, F. C., 1966. Comments on the Delphinoidea. Whales, Dolphins, and Porpoises, pp. 7-31. K. S.
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FRASER, F.C. and P. E. PuRVEs, 1960. Hearing in cetaceans, evolution of the accessory air sacs and thestructure and function of the outer and middle ear in recent cataceans. Bull. British Mus. Nat. Hist.,7(1): 1-140, pls. 1-53.
GRAY, J.E., 1866. Catalogue of seals and whales in the British Museum. British Museum, London. · 402 p.
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KELOGG, R., 1924. A fossil porpoise from the Calvert formation of Maryland. Proc. U.S. Nat. Mus., 63 (14):1-39, pls. 1-18.
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KELLOGG, R., 1928. The history of whales-Their adaptation to the life in the water. Quarterly Rev. of
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75(3354): 101-151, pls. 1-21.
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APPENDIX I
Key to genus or species by means of the morphology of tympanic bulla or periotic.

Tympanic bulla
al Sigmoid process is globular. Tympanic bulla is not compressed laterally. Anterior
spine and elliptical foramen are absent. Posterior process is large and funnel shaped.
Interprominential notch is wide and opens posteriorly. Involucrum is thick. Lengthof tympanic bulla 24 to 39 mm.
Kogia
bl Anterior margin of the lateral wall is convexed.
K. breviceps
b 2 Anterior margin of the lateral wall is concaved .
................................................... K. simus
a2 Sigmoid process is of a large square and thin. Its dorsal margin is longer than thelateral.
cl Lateral furrow is absent. Outer and inner posterior prominences are small, andthey situate on a plane including the lateral margin of sigmoid proces. Involucrum
is thick. Elliptica lforamen is absent. Posterior process is long and finely laminated. Length of tympanic bulla 55 to 63 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Physeter catodonc 2 Lateral furrow is conspicuous. Lateral margin of sigmoid process is twisted
posteriorly.
.. ................................................. Ziphiidae
d 1 Posterior prominences are large. Interprominential notch is wide.
e1 In the ventral view the anterior part of tympanic bulla is triangular andnarrow. Length of tympanic bulla 63 to 71 mm .
................................................... Berardius
e2 In the ventral view the anterior part of the outer and inner border is nearlyparallel.
f1 A small crest is present on the postero-lateral tip of outer posterior prominence.
.. .. . . . .. .. . . . . . . . .. . .. . . . . .. . . . .. .. .. . . . . . . . . .. .. . T asmacetus
f 2 Outer posterior prominence is globular or cylindrical. Length of tympanic
bulla 39 to 54 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesoplodon
g2 Ventral keel situates on the line extended from inner posterior prominence.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. carlhubbsi, M. stejnegeri,
M. europaeus, M. mirus
g 2 Ventral keel situates outer side of the line extended from inner posterior
prominence.
M. densirostris,
M. ginkgodens
d 2 Interprominential notch is shallow and narrow.
h 1 Outer posterior prominence is thin and has a small keel on the posterolateral
tip. Tympanic bulla is flat. Length of tympanic bulla 51 to 60 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .:(,iphius cavirostris
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Outer posterior prominence is thick and has no keel on the postero-lateral tip.
Tympanic bulla is cylindrical. Length oftympanic bulla 54 mm (1 example).
.. . . . .. .. . . . . . .. .. .. . . .. .. . .. . . .. .. . . .. . .. .. . .. . .. . Hyperoodon
a 3 Dorsal margin of sigmoid process is equal or shorter than the lateral margin.
il Lateral and median furrows are present. Sigmoid process is thick.
jl Anterior part of the ventral wall is conical. Elliptical foramen usually opens.
k1 Median furrow is wide and deep, and has fine needle-like processes in it.
Anterior spine is long. Lateral margin of sigmoid process is straight. Lengthof tympanic bulla 4 7 to 64 mm.
.. . . .. .. . . . . . .. .. . .. . . . . . .. . . . .. . .. . . . . .. . .. . . . . . . . Platanista gangetica
k 2 No needle-like process in the median furrow. Lateral margin of sigmoid
process convexes posteriorly.
11 Tympanic bulla is wide (63 to 71 % of the length) with the inner projectionof involucrum. Median furrow is narrow. Length of tympanic bulla 38 to
46mm.
. . . .. . . . . . .. .. .. . . . . . .. . .. . . . . .. . .. . . . . . . . . .. . . . . .. Inia geojfrensis
l2 Involucrum does not project interiorly. Width of tympanic bulla is 51 %of the length (1 example). Length of tympanic bulla 47 mm (1 example).
. .. . . . . .. .. . . . . . . . . .. .. . . . . .. . .. . . .. .. . . . . . . . .. . .. . Lipotes vexillifer
j 2 Inner border of ventral wall is concaved, and the anterior part is square. Posterior branch oflower tympanic aperture is wide (17. 7% of the length, 1 example).
Elliptical foramen closed. Length of tympanic bulla 24 mm (1 example).
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pontoporia blainvillei
i2 Lateral furrow is absent. Median furrow is absent or vaguely present. Sigmoid
process is thin and long.
m 1 Posterior process oftympanic bulla extends posteriorly. Posterior branch oflower
tympanic aperture is wide. Tympanic bulla is not compressed bitaterally.
Anterior spine is absent.
n 1 Facet for posterior process of periotic has ridges and keels. Involucrum
convexes.
o1 Anterior tip of tympanic bulla and outer posterior prominence projectventrally, and when seen from the lateral side the ventral contour IS
saddleshaped. Length of tympanic bulla 40 to 45 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Delphinapterus leucas
o 2 When seen from the lateral side, the ventral contour is nearly straight.
Shallow median furrow is present. Length of tympanic bulla 36 to
40mm.
.. . . .. .. .. . . . . . . .. .. .. .. . . . . .. .. . .. . . . . . .. .. . . . . . . . Orcaella brevirostrisn 2 Facet for posterior process of periotic is smooth. Weak median furrow IS
present.
pl Outer posterior prominence is cylindrical. Posterior process is thick andspindle-shaped. Length of tympanic bulla 27 to 32 mm.
. . .. .. .. . . .. . .. .. . . .. . .. .. . .. . . . . .. .. .. . . . . .. .. . . . . Neophocaena phocaenoides
p 2 Outer posterior prominence is flat. Posterior process is flat and square.
q 1 Ventral keel is high. Length of tympanic bulla 30 to 37 mm.
. . . . . . . . . ... . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phocoenoides
q 2 Ventral keel is low. Length of tympanic bulla 28 to 34 mm.
................................................... Phocoena
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m2

79

Posterior process of tympanic bulla extends to postero-lateral or lateral direction.
Anterior spine is usually present. Posterior branch of lower tympanic apertureis not wide.
r 1 Tympanic bulla is strongly compressed laterally. Inner posterior prominence
is short, and not extended posteriorly beyond the base. Ventral keel is prominent. Median furrow is absent.
s1 Width of tympanic bulla is 37 to 42% of the length. Ventral keel ishigh and sigmoidal. Anterior spine is absent and elliptical foramen isusually absent. Length of tympanic bulla 50 to 51 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Monodon monoceros
s2 Width of tympanic bulla is more than 42% of length. Anterior spine ispresent.
t 1 In the ventral view anterior margin is triangular, and the anterior spine
situates at the center. Anterior part of lateral wall is narrow. Inner
margin of ventral wall is straight. Surface of ventral keel is smooth.
Length of tympanic bulla 34 to 38 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peponocephala electrat 2 Inconspicuous anterior spine situates nearly at the center. Anterior partof lateral wall is wide. Involucrum is short. Inner margin of the bulla
concaves. Length of tympanic bulla 39 to 42 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Feresa attenuata
t 3 A plate-like or semitubal anterior spine situates in front of ventral keel.
Anterior parts of ventral wall and of lateral wall are narrow and pointed.
Inner margin of ventral wall is slightly convexed. Ventral keel is lower
at the center. Length of tympanic bulla 36 to 52 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Globicephalat 4 Anterior spine situates in front ofinvolucrum. Anterior part of the lateralwall is wide. Ventral keel is conspicuous. Inner margin of the ventral
wall slightly concaves. Length of tympanic bulla 38 to 47 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grampus griseusr 2 Tympanic bulla is not compressed laterally.
u 1 Ventral keel continues from inner posterior prominence to anterior end of
involucrum. Inner posterior prominence projects posteriorly beyond thebase. Median furrow is absent. Length of tympanic bulla is less than
45mm.
v 1 Contour of anterior margin of ventral wall is oval. Ventral keel ishigh. The thickness of inner posterior prominence is nearly same withthat of outer posterior prominence. Length of tympanic bulla 34 to
42mm.
................................................... Tursiops
v 2 Contour of anterior margin of ventral wall is rectangular, and has small
tubal anterior spine at the center. Ventral keel is high. Inner posterior
prominence is thinner than outer posterior prominence. Length of tympanic bulla 28 to 35 mm.
.. . ... .. . . .. ... .. . ...... .. . .. ... . . ...... ..... ... . . . Stenellav 3 Contour of anterior margin of ventral wall is narrow rectangular. Ventral
keel is wide and flat. Length of tympanic bulla 32 to 35 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lissodelphis borealis

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KASUYAu2

Ventral keel does not reach the anterior end of tympanic bulla. Inner
posterior prominence projects posteriorly beyond the base. Median furrow
absent.
w 1 Ventral keel is inconspicous and fades at slightly anterior of the middleof the bulla. Ventral wall is nearly smooth except a hemispheric prominence at the antero-mesial corner. Interprominential notch is wideand U shaped. Length of tympanic bulla 30 to 35 mm.
................................................... Delphinus
w 2 Ventral keel is high only at the posterior part, and ends nearly at the
middle of the bulla. Two vague longitudinal keels are present on the
median line and in front of outer posterior prominence. Length oftympanic bulla 32 to 39 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lagenorhynchus
w 3 Ventral keel is high and reaches at the point about 1/3 from the anterior.
There is a deep groove on the ventral surface along the anterior endof ventral keel. Anterior part of the bulla is cylindrical. Vague longitudinal keels are observed same with Lagenorhynchus. Length of tympanic
bulla 36 to 42 mm.
. . .. .. . .. . . . .. .. .. . .. . .. .. . .. . .. . .. . . . .. .. .. .. . . .. . Steno bredanensis
u 3 Ventral keel is almost absent. Median furrow absent. Tympanic bulla iscylindrical. Length of tympanic bulla is more than 45 mm.
x1 Both posterior prominences are arranged in parallel. Inner margin of
the bulla is straight. Length of tympanic bulla 49 to 51 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pseudorca crassidens
x 2 Posterior prominences opens posteriorly at the angle of about 45°. Elliptical foramen is absent. Length of tympanic bulla 70 to 85 mm.
. .. . .. .. .. . . . . . . .. .. . .. . . .. .. . .. . . .. . .. .. . . . . . .. .. . Orcinus orca
u 4 Median furrow or similar structure is present. Ventral keel low. Ellipticalforamen is usually absent. Small in size.
y1 Inner posterior prominence projects posterioly beyornd the base. Vague
keels is present at the outer border of median furrow. The inner angle
on the anterior border of ventral wall is steep. Length of tympanic
bulla 34 mm (1 example).
..... . . . . . .. ...... . .......... .... .. . . . . . . . . .. ... ... Sousa teuszii
y 2 Inner posterior prominence projects posteriorly beyond the base. Anterior base of outer posteriorly prominence swells. Anterior margin ofventral wall is oval. Length of tympanic bulla 27 to 29 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cepholorhynchus
y 3 Inner posterior prominence does not project posteriorly beyond the base.
Anterior margin of ventral wall is oval. Length of tympanic bulla 31
to 32 mm .
................................................... Sotalia

Periotica 1 Anterior process is shaped of a curved rod. Posterior process is bent postero-bentrally
at a right angles with superior process. Facet for posterior process of tympanic bullais small, and has weak keels and grooves.
b 1 Large accessory ossicle touches the cochlear portion and covers the dorsal part ofSci. Rep. Whales Res. Inst.,
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81

tympanic cavity. Superior process is massive and continuous in structure to thebase of posterior process. Aquaeductus Fallopii, foramen singulare, and ductus
endolymphaticus open in the fundus of internal auditory meatus. Length ofperiotic 5 7 to 69 mm.
.. . . . . . . .. .. .. . . .. .. . .. . .. . .. . .. . .. . . . . . .. .. . .. . . .. Physeter catodon
2b Accessory ossicle is small. Superior process is slender. Slender posterior process
is separated from superior process by a groove. Ductus endolymphaticus opens
outside of the opening of fundus of internal auditory meatus.
c1 Cochlear portion is flat. Anterior process is separated from superior process bya groove. A protuberance projects postero-ventrally from the antero-ventral
base of posterior process. Length of periotic 33 to 43 mm.
.. . . . . . .. .. . . . . .. . .. . . . . . . . . .. .. . . . . .. . . . . . .. .. . .. . Platanista gangetica
c 2 Cochlear portion is globular. Anterior process is continuous to superior process.
No protuberence at the antero-ventral base of posterior process. Length ofperiotic 52 mm (1 example).
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lipotes vexilli:fer
a 2 Anterior process is hemispheric or triangular pyramidal. Anterior and Posterior
processes are distinct from superior process. Posterior process is short. Facet for
posterior process of tympanic bulla is almost smooth.
d 1 Tip of posterior process is fan shaped.
e1 Anterior process is elongted triangular pyramidal. Length of periotic 66 to 76
mm.
Berardius2e Anterior process is short, and the triangular pyramidal part is roundish. Lengthof periotic 54 to 63 mm.
Ziphius cavirostris2d Posterior process is slender, and not wide.
f1 Anterior process forms a long triangular pyramid with the clear ridges. Length of periotic 61 mm (1 example).
.. . . . . .. . .. . .. . .. . . . . . . . .. .. . . . . . .. . . . . . .. .. . . . . . . . Hyperoodon
f 2 Anterior process is hemispheric, and has a small protuberance at the anterior
tip. The surface of periotic is smooth and roundish. Small in size, 41 to 52 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mesoplodon
g1 Dome shaped protuberance is formed on the dorsal surface of superior process.
Length of periotic 41 to 45 mm.
.. . . . . . . .. . . . . . . . .. . . . . . . .. . .. . . . . . . . . . . . . .. . . . . . .. M. europaeus
M. ginkgodens
g 2 No dome shaped protuberance on the superior process. Length ofperiotic 44
to 52 mm.
M. densitostris
M. carlhabbsi
M. stejnegeria 3 Anterior process is flat and spool shaped. A plate-like protuberance is on the tipof posterior process. Aquadeuctus Fallopii opens out side of the opening of fund us
of internal auditory meatus .
................................................... Kogia
h 1 Dorsal contour of upper tympanic aperture forms small semicircle. Length of
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KASUYA

periotic 24 to 31 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . . . . K. breviceps
h 2 Dorsal contour of upper tympanic aperture is nearly straight. Length of periotic
22 to 30 mm .
................................................... K. simus
a 4 Anterior process is flat, and its anterior margin is rectangular.
il Posterior process is short. Cochlear portion is spheric, and its diameter is morethan 54% of the tympanic length.
jl Periotic is short. Anterior process very short. Length of periotic 20 mm(1 example).
Pontoporia blainvillei
j 2 Periotic is large. Length of periotic 25 to 31 mm.
Inia geojfrensis
il Posterior process extends posteriorly and not short. Cochlear portion is less than
53% of periotic length.
k1 Facet for posterior process of tympanic bulla is smooth. Posterior process is rod
shaped. Length of periotic 26 to 32 mm.
l1 Posterior process is slender and conical, and the tip is pointed.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Neophacaena phocaenoides
12 Tip of posterior process is blunt. Faint constriction is on the base of posterior process.
. . . . .. ... . .. ......... ... .. . ... ... . . . ... . . . . . . . .. .. . Phocoenoides
l3 Tip of posterior process is blunt. No constriction on the base of posterior process.
. . ......... ... . . . . . .. .. . . .. .. . . .. .. . . . . ... .. . . . . . .. Phocoena
k 2 Facet for posterior process of tympanic bulla has ridges and grooves. Posterior
process is stout.
m 1 Posterior process is wedge-shaped. Irregular grooves are present on thedorsal surface of posterior process. Length of periotic 37 to 41 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Delphinapterus leucas
m 2 Posterior process is of triangular rod with spongy structure on the tip.
Length of periotic 34 to 41 mm.
Orcaella brevirostris
i3 Posterior process extends laterally or postero-laterally and is not short.
n 1 Periotic is large. Anterior, posterior, and superior processes are very massive,
but cochlear portion is relatively small (diameter is 31 to 39% of periotic
length). Periotic length 73 to 88 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Orcinus orca
n 2 Periotic is small, less than 50 mm in length. Monodon and most of the generaof Delphinidae are included, and their identification is usually difficult.
o1 Needle-shaped processes are formed on the dorsal surface of superior process.
They are conspicuous in older individuals, and weaker in the following order.
pl Opening of fund us of internal auditory meatus is round. Crista transversa
is high (characteristics found only in this genus among the following 4
genera). No flat area is on the dorsal surface of superior process. Lengthof periotic 37 to 50 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Monodon monoceros
p 2 Wide and elevated flat area is conspicuous on the dorsal surface of superior
process. Posterior process is thick and short, and has the spongy structure
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

TYMPANO-PERIOTIC BONES

83

on the tip (found only in this genus among the 4 genera). Length ofperiotic
34 to 46 mm.
.. . .. . . .. .. . . . . .. .. . . .. . .. . .. . . .. .. . . . . . .. .. .. .. .. . Grampus griseus
p 3 Flat area on the superior process is low, and distinguished unclearly fromthe rest of the part. Tip of posterior process is thin. The contour ofanterior, superior, and posterior processes is smoothly round. Length ofperiotic 33 to 44 mm.
. . . .. .. . . . .. .. . .. . . . . .. . . . . .. . . . . . .. .. . .. . . . . . .. . .. Globicephalap 4 Flat area on the dorsal surface of superior process is oblique and notelevated from the rest of the area. Longitudinal keel is present on the
inner side of dorsal surface of superior process. Opening of fundus ofinternal auditory meatus is long. Length of periotic 31 to 38 mm.
................................................... Tursiops
o 2 No needle-shaped process is formed on the dorsal surface of superior process.
Crista transversa is low.
q 1 Longitudinal keel is conspicuous on the dorsal surface of superior process,and its outer area forms a flat slope. Anterior process is nearly straight.
Length of periotic 42 to 49 mm.
. .. . . . . . . .. . . . . . . .. .. .. . . .. .. . .. . . .. .. .. .. .. . . . .. . . Pseudorca crassidens
q 2 Anterior process is thick. In the lateral view, the dorsal contour ofant~rior and superior processes is straight. Dorsal surface of superior
process is not wide. Length of periotic 35 to 38 mm.
.. . . . . .. . . . .. . . .. . . . . .. . . . . . . . .. . . . . . .. .. . .. . .. . . .. Feresa attenuata
q 3 Dorsal surface of superior process is wide and flat. Length of periotic
30 to 35 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peponocephala electra
q 4 The area posterior of the opening of fundus of internal auditory meatus iswide and flat. Length of periotic 33 to 36 mm.
.. . . . . .. . . . . . .. .. . . . . . .. .. . . . . .. . .. . . . . . .. . .. .. . . . . Steno bredanensis
q 5 Aquaeductus cochleae and ductus endolymphaticus are surrounded by aflat area, and open in a same plane. Length of periotic 30 to 33 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lissodelphis borealis
q 6 In the lateral view, the dorsal contour of anterior, superior, and posterior
processes is round. Length of periotic 28 to 33 mm.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lagenorhynchus
q 7 Superior process is slender, and surrounded by two planes of dorsal andand lateral sides. Length of periotic 33 mm (1 example).
.. . . .. .. . . . . .. . .. . .. . .. . .. . . .. .. . . . . .. . .. . . . . . . . . . . Sousa teuszii
q 8 Superior process is slender, and surrounded by three planes. Length ofperiotic 27 mm (1 example).
......... ... . . . . . . .. . .. . ... .. . . ........... ... ... .. . Sotalia
q 9 Opening of aquaeductus cochleae projects posteriorly. One longitudinal
keel is present on the dorsal surface of superior process. Length ofperiotic 26 mm (1 example).
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cephalorhynchus
q 10 Small periotics (24 to 32 mm in length) other than the above genera
probably belong to Delphinus or Stenella. As the individual variation islarge, the identification is most difficult in these genera.
Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

~~..... .
~~~..;""'i-.~ ::.
~

~

~

?:
::,.,

C

47. I, 63.5
43.7, 58.3
34.3, 37 .2
27.3, 30.I
24.7, 29.2
33.3, 38.9*

2.4, 3.6
11.0, 13.1
2.7, 4.3
0.9, 4.5

7
7
7

7

7

7

7

7

7

2

4

5

6

7

8

9

7
7

A :
B :
C:
D :
E :

D

64. 7, 77 .0

JOO
23.9, 35.9
55.3, 66.5
9.9, I3.7
5.6, 9.8
26.3, 35.0
38.3, 44.8

4.5, 5.7
20.3, 25.9
4. 7, 9.1
I .9, 8.2

IOO
90.0, 91.8
58.6, 73.2
47.4, 59.6
44.3, 54.4
61.3, 74.8

E'

5
5
5

30.8
41. 7

71.4

5

8. I

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

5

B

37.6
30.3
61. 7
Il.8

5.3
23.4
6.4
4.9

52.4
91.3
68.2
54.6
50.9
69.2

c

+

25. 7, 30.4
10. 7, I5.6
21.4, 25.2
3.8, 4.8
2.6, 3.6
8.2, II.I
I4.2, I8.2

Outer~ Inner

2.8, 3.4
9.7, 10.2
3.5, 4.2
I .9, 5.0*

38.2, 45.6
32.0, 41.1
25.3, 28.I
16.6, 18.9
25.5, 28.0
29.8, 34.8

60.8, 67.6

JOO
41.6, 58.3
79.6, 90.0
14.7, 18.3
9.7, I3.6
3I.9, 36.6
54.3, 68.5

6.3, 8.5
22.6, 27.5
7.9, Il.5
4.3, 11.0

JOO
83.8, 91.5
59.4, 68.5
39. I, 44.8
60.3, 70.3
74.0, 81.4

D2
Inia geoffrensis

Position of measurement or observed characters (see Table 3 in the text).
Number of individuals observed.
Observed minimum and maximum in mm .
Observed minimum and maximum in percentage of the standard length.
Mean value in mm (positions I and 13) or in percentage of the standard length.

* Unmeasurable

22

+
+

7

6
7

Inner

33.4, 42.3
9.4, 15.2
21.9, 24.8
3.6, 5.3
2.2, 3.8
10.0, I3.0
14.5, I6.2

12
I3
14
I5
16
I7
I8
I9
20
21

7

11

7
7
7
7
7

7

6

IO

3

I

Platanista gangetica

B

A

65.7

34.3
63.7

I I. 7

26.9
48. 7
87 .o
I5.2

25. I
9.5
8.5

7 .8

41. I
88.0
64.5
42.7
65.3
77.4

E

B

+

52.0
I4.0
24.0
3.0
3.0
IO.O
I9.5

Outer

2.2

47.I
44.4
29.3
22.4
24.0
27.3
24.I
4.8
5.0
1.3

c

ll0.4

IOO
26.9
46.2
5.8
5.8
19.2
37.5

IOO
94.3
62.3
47.6
5I .O
58.0
51.2
I0.2
J0.6
2.8
6.0

D

3
Lipotes vexillifer
B

20.0
9.5
16.2
4.0
2.8
8.4
I3.6

Inner

0

24.3
21.9
I 7. I
I3.2
14.9
20. I
I3.5
3.0
6.0
4.3

c

82.3

JOO
47.5
81.0
20.0
I4.0
42.0
68.0

0

JOO
90.0
70.3
54.3
61.3
83.0
55.5
I2.4
24.6
I7.7

D

4
Pontoporia blainvillei

APPENDIX II. TABLE OF MEASUREMENTS AND SOME CHARACTERISTICS OF TYMPANO-PERIOTIC BONE.

~

:;::
~
c:::

~

.;~

S'

~

~

~"
~

-'""~
.......
~~

""~

?:
~
? !""·

19
20
21
22

18

12
13
14
15
16
17

27.1, 31.4
8.1, 9.9
16.2, 18.4
3.1, 5.0
1.4, 2.8
8.9, 15.8
13.2, 15.2

0
Outer

18

19
19
19
19
19
19
19
15
19
19
19
19

10

11

8
9

7

5
6

3
4

2

c

27.7, 31.5
28.4, 32.1
21.7, 25.4
16.1, 19.4
16.0, 20.0
24.1, 28.1
16.7, 19.3
2.9, 5.4
6.1, 7.4
2.4, 3.9

B

/

29.9
29.7
58.5
12.7
7.0
47.3
47.3

99.7

93.7, 105.8

Closed100
26.6, 33.6
55.5, 64.3
10.2, 16.4
4.5, 9.2
30.4, 51.6
45.1, 51.4

0

D
E
100
30.1
98. 7, 108.0 101. 7
74.8, 83.2
80.4
56.1, 63.2
61.1
57.8, 65.8
62.3
81.5, 94.3
88.3
56.2, 63.5
59.4
10.4, 17.8
14.1
20.1, 24.6
22.0
7.6, 12.8
10.3

5
Neophocaena phocaenoides

19
19
17
17
18
17
19
19
17

l

A

3
3
3

3

3
1

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

3

B

Continued.

26.9, 30.0
10.1, 10.6
15.2, 16.4
3.3, 4.8
2.5, 3.7
8.6
12.0, 12.6

0
Inner

30.5, 33.7
28.3, 30.3
23.2, 24.4
17.7, 18.0
19.4, 21.0
24.2, 25.0
15.2, 17.0
4.6, 5.4
5.1, 5.8
3.1, 3.9c87 .0, 91.0

100
34.2, 39.0
52.7, 57.6
11.8, 16.2
10.0, 12.3
32.0
40.0, 44.6

0100
89.3, 92.8
70.3, 77.4
53.1, 58.0
62.8, 63.7
75.2, 80.3
49 .1, 50.4
13.6, 17.7
16.7, 18.0
9.2, 12.8

D

6
Phocoena ph. vomerina

APPENDIX II.

88. 7

43.0

28.3
36.8
54.9
13.7
11.4.

Closed

31.9
91.6
74.6
56.0
63.4
77 .1
49.5
16.2
17.4
10.6

E

3

3
3
3

3

3

3

3

3

3

3

3

3

3

3

3

3
3

3

3

3

3

B

7

Inner

28.2, 30.4
9.4, 9.8
15.3, 16.l
3.6, 4.3
2.8, 3.4
10.8, 11.8
11.2, 11.9

028.4, 31.4
27 .8, 30.1
21.9, 22.5
15.7, 16.3
18.5, 19.9
22.7, 24.9
14.8, 16.9
3.6, 4.9
5.3, 5.9
2.7, 3.3c96.8, 99.6

100
32.6, 34.8
53.0, 56.9
12.8, 15.2
9.9, 12.0
37 .6, 41.8
38.9, 42.0

0100
95.9, 97.9
71.7, 77.5
52.0, 56.3
59.0, 70.1
79.3, 87.3
51.7, 55.3
12.6, 15.6
18.2, 20.8
9.5, 10.8

D

Phocoena ph. phocoena

98.3

29.0
33.7
54.8
13.7
11.0
39.7
40.8

Closed

29.5
97.0
75.3
54.4
65.3
82.0
53.6
14.6
19.2
10.3

E

00
<:.11

(/)

zt>l

0

t:d

a

......

5~

:xi

~

~0

~

~

~~
~.:

.

t';~
~

.~~""

~

~

::ti

~

I

I

I

I

I

I

I

I

-

-

12.6

26.8
10.3
15.2
3.4
2.7

I

I

Outer~ Inner

I

I

I

I

I

I

I

I

I

91.0

47.0

100
38.4
56.7
12.7
10.4

100
94.3
78.0
54.5
57.6
77 .3
63.0
14.6
20.6
7.5
0

29.5
27.8
23.0
16.1
17.0
22.8
15.6
4.3
6.1
2.2
0

I

I

2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

I

D

c

/

6
6
6
6
6
6
6
6
6
5
5
6
6
6
6
6
6
5
6
6
6
6

B

-

-

28.7, 33.2
10.9, 12.5
15.7, 17.5
2.9, 4.6
1.9, 3.2
11.4, 14.4
11.9, 13.8

Inner

32.1, 36.9
29.4, 34.2
24.1, 26.9
19.4, 21.0
19.1, 22.5
25.3, 29.2
15.1, 18.3
4.9, 6.7
5.4, 8.0
2.5, 3.7
0c86.2, 97.8

100
35.8, 39.4
50.9, 56.5
8.7, 16.0
7.3, 11.2
38.8, 44.4
37.5, 43.5

100
90.9, 97.2
72.9, 77 .5
54.2, 60.8
59.0, 69.8
76.4, 82.4
44.9, 52.4
14.7, 20.8
16.8, 21. 7
7.7, 11.5
0D

9Phocoenoides dalli

8Continued.

Phocoena sinus

B

A

APPENDIX II.

92.0

31.2
37.5
53.8
12.6
8.6
41. 7
40.7

Closed

33.9
92.9
75.4
58.7
63.0
79.2
48.2
17.6
19.8
8.9

E

6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
5
6
6
6
6

B

29.0, 31.6
10.8, 11.7
15.7, 17.1
3.1, 5.5
2.4, 3.6
11.7, 12.1
12.2, 13.2

Inner

30.9, 34.1
27.5, 31.5
23.4, 25.7
17.8, 19.4
18.5, 20.5
22.8, 25.9
12 .9, 16.8
4.4, 6.4
6.4, 7.3
2.8, 4.30c89.0, 100.6

10036.4, 38.6
52.8, 54.1
10.2, 18.7
8.3, 12.4
37.9, 41.4
41.5, 43.2

100
89.0, 93.9
68.5, 81.9
54.0, 61.8
55.4, 60.8
67.9, 82.5
37.8, 53.5
12.9, 20.4
19.6, 23.6
9.1, 12.6
0DJO
Phocoenoides truei

93.5

30.1
37.3
53.6
13.2
10. l
39.6
42.3

Closed

32.3
91. l
75.4
58.0
61.6
74.5
45.4
17.0
20.8
10.5

E

:;

c"'

~

>

co
c;i

~~
::> r·~

S<~'";i;i~~~~._::i::i..."°~~6

27.4, 31.1
10.0, 11.6
18.9, 20.4
1.2, 2.6
1.3, 3.0.
10.3, 14.0
12.1, 13.8

+

6

6

6

6

6
6

6

6

6

6

6

Outer

6

11

6

12
13
14
15
16
17
18
19
20
21
22

6

6

8

9

6

7

10

6

5
6

6

6

6

2

85.4, 92.0

100
35.8, 38.6
65.6, 72.6
4.1, 9.5
4.2, 10.9
37.3, 46.8
42.8, 48.6
2
2

44.1
45.5

88.1

2

2

2

2

2

2
2

7.7

2

2

2

2

2

2

2

2

2

2

2

2

2

B

28.6
37.4
68.7
7.0

E

32.6
95.8
67.6
51. 7
55.0
67.9
47.8
14.4
14.4
3.6
15.6

D

100
92.9, 97.5
64.0, 70.0
48.4, 53.8
50.9, 58.0
64.0, 70.2
44.6, 49.5
12.5, 16.0
13. 2, 15. 2
3.0, 4.5
10. 7, 18.5c30.5, 35.0
28.3, 33.5
20.4, 22.9
16.1, 17.5
16.8, 18.6
21.4, 22.4
15.0, 15.9
4.0, 5.2
4.1, 5.0
0.9, 1.4
3.4, 6.3

6+27.9, 30.1
10.0, 11.0
19.0, 19.8
1.2, 2.2
1.6, 3.4
12.2, 12.2
13.4, 14.1

Outer

31.8, 34.4
29 .5, 31.8
22.1, 22.9
16.2, 17.6
18.6, 19.7
22.1, 23.2
15.2, 16.4
4.6, 4.8
4.8, 5.7
0.8, 1.0
4.9, 6.2cD

83.3, 92.8

100
33.7, 39.4
63.1, 68.1
4.0, 7.9
5.4, 12.2
43.7, 43.7
45.2, 49.1

100
91.2, 93.7
66.3, 69.5
48.4, 53.8
55.6, 58.4
66.1, 72.0
44.2, 49.8
13.7, 15.1
14.0, 17.0
2.3, 3.1
14.6, 18.1

12Delphinus delphis

11

Continued.

Delphinus bairdi

B

3
4

A

APPENDIX II.

B

14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14
14

13

+

29.0, 32.7
10.9, 14.0
18.6, 21.7
1.3, 3.8
2.0, 3.8
10.9, 16.4
13.3, 14.5

Outer

33.0, 38.4
30.9, 36.8
22.4, 25.2
17 .2, 19.8
18.8, 22.2
22.1, 25.2
14. 2, 17. 7
4.3, 5.7
4.2, 6.1
0.6, 2.1
4.0, 6.3

c78.4, 91.8

100
37.1, 43.l
61.5, 70.5
4.4, 12.2
6.7, 12.3
37.2, 54.5
44.6, 49.5

100
92.0, 98.8
64.0, 70.3
49.3, 54.8
53.2, 64.1
64.4, 71.2
42.0, 49.4
12.5, 16.8
12.5, 17.1
1. 7, 5.9
10.4, 18.4

D

Lagenorhynchus obliquidens
E

86.4

30.6
40.0
66.4
9.4
9.1
42.4
46.1

35.4
96.0
67.4
52.3
57 .3
67.8
45.5
14.4
14.8
3.9
14.0

°'.....

rJJ

~J:rj

t.:x:l

0

,__,

~::0
0..,i

0

z~

~

..,i

><:

~ ,,:~" "'..u-. ~~~? "'"":>;,'.?: ~

~

~

:>;,

:-·

~

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

A

3
3
2
3
2
2
3
3
2
2
3
3
3
3
3
3
3
3
3
3
3
3

B

+

28.4, 30.0
10.8, 11.8
17.9, 19.5
1.1, 1.3
1.8, 2.2
13 .4, 14 .3
13.1, 14.0

Outer

32.3, 33.4
30 .6, 31.6
22.4, 23.3
16.6, 17.3
17.4, 18.0
22.3, 23.3
16.0, 16.5
4.0, 4.4
5.5, 6.2
0.9, 0.9
3 .1, 4.4c87.0, 90.0

100
37.2, 29.4
63.0, 67.3
3.9, 4.3
6.3, 7.6
46.2, 47.6
46.2, 48.3

100
91.7, 98.0
69.5, 69.6
51.5, 51.7
54.0, 54.0
69.0, 69.7
48.0, 49.6
12.0, 13.6
16.5, 19.2
2. 7, 2.8
9.6, 13.2

D

88.3

29.1
38.6
64.6
4.1
6.8
47 .1
46.9

33.0
94.7
69.6
51.6
54.0
69.4
49.0
12.5
17.9
2.7
11. 7

E

3
3
1
2
2
1
3
3
1
1
2
2
2
2
2
2
2
2
2
3
3
2

B

+

31.8, 32.4
13.5, 14.1
20.9, 21.4
1.8, 1.8
2.9, 3.3
15.5, 15.6
14.2, 14.3

Outer

36.6, 37.6
35.0, 35.8
24.5
19.1, 19.3
22.3, 22.4
27 .8
20.1, 20.5
5.0, 5.7
5.7
1.1
I. 7, 2.7c85.8, 88.5

100
42.5, 43.5
65.8, 66.0
5.6, 5.7
7.7, 10.4
48.1, 48.8
43.8, 45.0

100
94.3, 98.0
65.0
51.4, 51.5
59.4, 60.4
74.0
54.2, 56.0
13.7, 15.2
15.2
2.9
4.6, 7.2

D

15
L. albirostris

14

Continued.

Lagenorhynchus acutus

APPENDIX II.

54.9
14.6

37 .1
96.2

E

I

1

I

I

I

I

I

+

15.0

31.6
12.7
22.0
I. 7
2.8

Outer
I

I
I

c
33.5
32.8
23.3
23.2
19.1
23.7
16.5
4.2
5.5
1.1
4.0

1
1
1
1
1
1
1
1
1
1

B

D

94.5

47.6

100
40.2
69.8
5.4
8.9

100
98.0
69.5
69.3
57.0
70.7
49.2
12.5
16.4
3.3
11.9

B

I

I

1

1

I

I

I

1

I

I

1
1
1
1
1
1
1
1
1
1

+

12.8

30.1
13.9
19.7
1.5
1.8

Outer

92.0

42.6

100
46.2
65.5
5.5
6.0

0

0

D

100
94.5
69.0
51.4
58.0
40.1
47.4
14.4
14.7
32.7
30.9
22.5
16.8
19.0
13 .1
15.5
4.7
4.8

c

17
L. australis

16
L. obscurus

~

~

c:::

r'1

;i..

°"°"

.;~

S"

~

~

~ f:..

~~

.....

u"'1~

""::,.,

~ K>
? :"·

7

7

2

3
4
5
6
7

Outer

33.l, 36.0
11.3, 13.6
21.2, 24.3
l.O, 2.3
2.4, 3.8
13.7, 17.8
15.5, 18.3

+

7

7

7

7
7
7
7
7

7
7

II

12
13
14
15
16
17
18
19
20
21
22

7

7

6

7

8
9
lO

7

7

7
7

7

100

36.8, 41.8
35.7, 40.8
25.5, 27.7
18.8, 21.5
20.3, 25.0
25.5, 28.7
19.l, 21.7
4.3, 5.6
4.5, 6.3
I.I, 2.5
3.4, 6.1

7I

84.7, 98.0

100
32.1, 40.7
62.0, 73.5
3.0, 6.8
7.2, 11.3
41.1, 52.3
46.4, 54.5

96.5, 99.7
66.3, 72.0
51.3, 55.0
55.3, 60.3
67.7, 74.9
50.7, 57.2
11. 3, l4. 7
12.2, 17.2
2.6, 6.4
9.0, 16.6

D

c
E

B

89.2

34.3
36.3
67.2
5.4
9.1
48.0
49.6

38.5
98.0
69.4
52.9
58.5
71.5
53.2
12.9
14.4
4.4
12.0
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6

6
6
6
6
6
6

+

30.2, 32.5
10.4, 11.8
19.3, 20.4
1.4, 2.4
2.0, 2.9
10.2, 13.5
13.0, 14.9

Outer

32.6, 34.1
32.1, 34 .3
22.0, 23.5
16.5, 18.1
17.8, 19.6
23.1, 25.1
14.0, 15.9
5.1, 6.3
4.7, 5.3
0.9, 1.3
2.6, 4.3c90.0, 97.5

100
34.2, 39.1
62.5, 64.3
4.6, 7.8
6.1, 9.3
33.4, 44.8
41.8, 48.8

96.5, 100.3
65.6, 71.2
49.2, 55.4
53.0, 58.9
68.3, 75.0
42.0, 48.5
15.4, 18.9
13.8, 16.0
2.6, 3.9
7 .8, 12.9

100

D

19
Lissodelphis borealis

18

Continued.

Steno bredanensis

B

A

APPENDIX II.

92.7

39.3
44.9

7 .9

30.9
36.7
63.3
6.3

33.4
99.0
68.8
52.5
55.3
70.9
45.5
16.6
14.7
3.2
10.4

E

14
14
14
14
14
13
14
14
13
14
14
14
15
15
15
15
15
15
15
15
15
14

B

/

20

5.6

3.0,

+

28.0, 31.9
10.8, 14.1
18.3, 20.6
0. 7, 2.1
I. I, 4.0
9.0, 14.0
13.5, 14.3

Outer

l.8

0. 7,

28.9, 34.3
28.0, 34.3
19.9, 22.9
15.8, 17.8
15.4, 18.8
20.9, 24.4
12.9, 16.0
3.1, 5.1
4.6, 5.6c88.1, 102.1

100
36.2, 45.6
60.3, 69.1
2.4, 8.1
3.9, 12.7
30.4, 47 .6
43.2, 47.6

90.0, 95.5
62.4, 72.4
49.3, 55.8
49.0, 55.8
63.3, 74.7
41.5, 47 .6
11.9, 15.2
13.6, 17.9
2.2, 5.8
8.8, 17.7

100

D

Stenella caeruleoalba
E

92.8

29.7
40.0
65.6
4.5
8.0
37.5
46.7

32.0
93.1
68.6
52.7
52.8
70.2
44.1
13. I
15.9
3.7
14.5

co

'°

rFJ.

l:rj

z0

C:I

0

.....

~
~
0>-l

~0

~

~

~• 1;:~~......
~~
~..;~

~

~

::ti

~

22

21

18
19
20

10
11
12
13
14
15
16
17

9

6
7
8

5

3
4

2

I

A

B

57.9
72.0
46.1

18.6
23.1
14.8

89.7

5.9
37.8
45.8

I. 7
10.9
13.2

+

39.9
66.3
4.5

11.5
19.1
1.3

4.3
13.4
5.3
16.5
1.2
3.7
5.5
17 .1
Outer
100
28.8

D

100
95.0
84.1
54.8

C

32.1
30.5
27.0
17.6

~

21
Stenella sryx

6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6

6

B

+

1.2, 2.8
9.0, 11.8
12.4, 13.5

17.0, 18.8
1. 7, 3. I

25.4, 28.5
9.5, 10.9

3.6, 4.5
0.8, 1.4
2.8, 5.3
Outer
2.7, 4.8
9.5, 18.1

85.1, 97.9

58.1, 67.9
6.7, 11.6
4.8, 10.3
33 .1, 44 .9
43.9, 53.2

34.9, 41.3

100

90.l

7.6
38.9
47.6

27.0
37.9
64.8
8.2

3.5
11. 7

11.2, 15.8
12.2, 14.7

68.5, 72.1
43.3, 50.4

53.6
70.7
46.4
13.5
13.9

68.8
52.4

65.8, 71.8
50.7, 54.2
50.8, 55.0

15.0, 16.9
20.1, 22.2
12.6, 15.5
3.3, 4.7

29.9
94.8

D

100
93.5, 96.9c28.0, 30.8
27.5, 29.2
19.4, 22.1
14.9, 16. 7

E

c

2

2

2

2

2

2

2

2
2
2

2
2
2
2

+

8.3, 8.3
12.3, 12.3

9.4, 9.5
16.7, 17.0
1.9, 2.0
1.7, 2.0

13.8, 15.7
14.5, 16.5
2.8, 3.3
6.9, 14.1

4.2, 4.5
4.3, 4.7
0.8, 1.0
2.1, 4.0
Outer
24.3, 24.4

2

2

84.7, 85.9

7

7

7

7

7

50.4, 50.6

7+

9.8, 12.4
18.0, 20.0
0.9, 1.8
2.2, 3.4
11.0, 14.5
13.0, 14.0

Outer
26.2, 29.6

7

7
7
7
7

22.0, 23.9
14.3, 15.6
4.2, 5.6
4.0, 5. 7
0.5, 1.2
0.7, 4.7

30.1, 33.8
28.2, 32.8
21.0, 22.5
15.3, 17.3
17.1, 18.lcE

80.5, 95.7

66.6
4.7
9. 7
46.1
61.9, 69.5
3.1, 4.9
7 .5, 12.5
35.3, 49.6
46.9, 50.5

88.0

48.5

28.2
38.3

71.4
46.8
14.9
15. 7
2.5
7 .2

31.3
95.4
68.6
51.7
55.6

100
36.3, 42.5

68.3, 77.0
42.9, 49.4
12.8, 17.6
14.0, 18. 7
1.5, 4.0
2.3, 14.1

100
89.7, 105.0
62.4, 73.5
45.2, 54.5
51.0, 59.0

D

24
Stenella attenuata

7
7
7
7
7
7

7

7

7.0, 8.2
34.0, 34.2

38.5, 39.1
68.4, 70.0
7 .8, 8.2

100

70.4, 70.7
46.4, 53.5

20.0, 21.5
14.1, 15.2

2

2

2

2

7

7
7

95.8
72.l
56.0
57.4

B

D

100
93.4,
69.1,
51.9,
55.4,

28.4, 30.4
27 .2, 28.4
20.3, 24.6
15.8, 16.0
15.9, 17.0

2
2

B

23
(?) Stenella longirostris

22

Continued.

(?) Stenella roseiventris

APPENDIX II.

~

r:n.

~
;i..

0

<.o

~~
!""'·

.:"'

to'

~

.~~"~
"'

~~
......

•

2

3
4*Closed on 1

2

2

2

2

2
2

2

3
3
3

2

2

2

2

2

8

9

2

7

10
11
12
13
14
15
16
17
18
19
20
21
22

2

5
6

2

2

2

2

B

2

A

+

29.8, 32.0
27.4, 29.8
21.0, 21.3
15.9, 16.4
17.8, 18.3
21.1, 21.7
14.5, 15. 7
4.1, 4.8
4.5, 4.7
0.8, 1.0
3.5, 4.3
Outer
25.9, 27.2
8.3, 9.6
16.6, 18.4
0.6, 1.0
2.1, 2. 7
10.4, 12.1
13.4, 13.6cDB

84.6, 89.2

100
30.6, 36.2
64 .0, 69 .4
2.3, 3.7
7.9, 10.1
39.2, 44.6
49.4, 51.3

100
91.5, 93.1
65.9, 71.1
51.1, 53.6
55.6, 60.7
65.9, 72.6
48.6, 50.8
13.7, 15.0
14.1, 15.7
2.5, 3.2
11.1, 14.4
2
3
3
3
3
3
3
3
3
3
3
3
3
3

3
3

3
2
3
3
2

3

+

33.8, 34.4
31.2, 32.2
22.5, 22.6
16.8, 17.3
17.6, 19.8
23.4, 23.6
15.0, 15.7
4.3, 5.0
4.7, 4.9
0.8, 1.2
3.4, 4.0
Outer
28.9, 29.6
10.4, 12.1
18.9, 19.9
1.3, 1.4
2.0, 2.3
10.8, 13.6
12.8, 13.9c81.5, 85.5

100
36.0, 41.9
63.8, 68.9
4.4, 4.8
6.8, 8.0
36.5, 47.0
43.6, 47.7

100
90.6, 95.2
65.6, 66.5
49.1, 50.3
51.4, 54.9
68.0, 69.8
43.6, 46.4
12.5, 14.8
13.9, 14.2
2.3, 4.1
9.9, 11.6

D

24b
Stene/la plagiodon

24a

Stene/la graffmani

APPENDIX II. Continued.

83.7

29.1
38.4
66.5
4.7
7.4
40.3
45.2

34.1
92.6
66.1
49.8
53.6
68.9
45.1
13.6
14.1
3.3
11.0

E

43
43
42
43
43
42
43
43
42
43
43
43
43
43
43
43
43
42
43
43
43
43

B

25

+

34. 7, 41.5
33.1, 40.0
23.9, 28.1
17.7, 21.7
18.9, 25.5
25.3, 30.2
17.4, 21.3
4.0, 5.9
4.6, 6.9
0.8, 3.5
0, 7.3Outer
31.7, 37.8
12.0, 18.0
20.5, 24.3
0.4, 3.4
1.2, 4. 7
12.0, 19.0
14.9, 17.5c80.4, 99.5

100
36.2, 52.6
56.7, 70.1
2.8, 10.1
3.4, 14.1
35.1, 52.8
41.9, 52.8

100
80.6, 99.2
65.6, 74.0
48.6, 55.9
52.5, 63.4
65.4, 79.2
45.2, 55.6
10.7, 15.5
11.3, 18.6
2.2, 9.2
3.8, 20.3

D

Tursiops truncatus (w. Pacific)

91.9

35.0
42.0
64.3
4.9
9.1
43.0
46.3

38.1
95.2
69.8
52.6
59.3
72.8
51. l
13 .1
15.0
4.5
12.1 *

E

~

"'

zt<:I

0

t;I:)

0

~

0

~

~0

~

~~
~.;~

......

vtJ-i ~"":::,.,.~ 1'""'~~:::,.,

~

3
3

6

7

12
13
14
15
16
17
18
19
20
21
22

II

10

8
9

3
3

3

3

3
3
3
3
3

3
3
3

+

31.9, 33.6
11.7, 13.7
21.1, 22.2
0.5, 1.9
3.0, 3.8
14.7, 19.9
15.8, 17.0

Outer

3

5

3
3

3

3
4

83.3, 87.5

36.6, 41.3
62.8, 66.5
1.5, 5.7
8.9, 11.2
44.2, 59.2
49.4, 50.3

100

95.9, 99.0
64.8, 68.3
45.2, 48.6
53.2, 54.0
68.3, 69.5
46.4, 51.0
11.2, 13.0
12.8, 16.6
4.2, 6.0
6.0, 13.6

100

38.3, 39.2
36.6, 38.8
25.4, 26.2
18.3, 19.0
20.5, 21.0
26.2, 27.2
18.2, 19.5
4.4, 5.0
1.9, 6.5
1.6, 2.3
2.3, 5.2

3
3
3
3

2

D

c

/

85.7

33.1
37.4
66.9
3.5
10.2
42.2
49.9

38.6
97.5
67.3
47.3
53.5
68.9
49.1
12.6
14.6
5.2
10.5

E

Outer

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

+
88.5, 89.0

33.4, 34.4
100
14.0, 14.0 40.7, 42.0
20.8, 23.9 62.3, 69.5
1.2, 2.2 3.6, 6.4
2.1, 2.6 6.1, 7 .8
15.2
45.4
15.3, 15.9 44.5, 47.6

D100
96.5, 97.5
67.5, 68.0
50.1, 53.0
55.4, 60.5
72.3, 74.0
44.6, 52.8
10.4, 12.3
12.3, 16.3
6.9, 7.2
7.2, 5.4

CB

37.5, 38.9
36.6, 37.4
25.3, 26.4
18.8, 20.6
20.8, 23.5
27.7, 28.1
16.7, 20.5
3.9, 4.8
4.8, 6.1
2.6, 2.8
2.8, 5.4

I

2

2

2

2

2

I

2

2

2

2

2

2

2

2

2

2

2

B

Continued.

2

/

26
T. gilli (e. Pacific)

25a

Tursiops truncatus (Atlantic)

B

A

APPENDIX II.

27

+

25. 7
10.1
16.6
2.6, 3.0
3.6, 4.6
9.5
12.1, 13.9

Outer

27.8, 28.7
21.8, 26.1
18.4, 19.4
14.5, 14.8
15.9, 16.7
18.3, 19.8
12.8, 12.9
2.8, 3.2
4.4, 4.8
I.I
0

C

92.5

37.0

100
40.9
64.6

100
89.3, 90.9
66.2, 67.6
51.6, 52.2
57.2, 58.2
65.8, 69.0
44.6, 46.4
10.1, II.I
15.3, 17.3
4.0
0

D

Cephalorhynchus spp.

2

2

2

2

2

2

2
2
2

2

2

2
2

2

2

2

2

B

D

0,

+

100
91.3, 91.4
67.0
49.6, 51.0
56.2, 57.3
70.4
48.6, 49.4
10.3, 13.5
13.0
5.4

+
83.5, 85.0

26.5, 26.7
100
8.4, 9.4 31.5, 35.5
18.1, 19.5 67.9, 73.5
1.4, 1.5 5.3, 5.7
1.5, 1.8 5. 7, 6.8
48.4
12.9
12.2, 12.8 45.8, 48.3

Outer

o, +

I. 7

31.4, 31.7
28.7, 28.9
21.0
15. 7, 16.0
17.8, 18.0
22.1
15.3, 15. 7
3.3, 4.3
4.1

c28
Sotalia spp.

~

~

lS

~~
? ~·
::ti

.:;:::..

t;;-.

~

~

~;:,.

~~

~""~
......

!\,)

22

5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21

4

3

2

A

B

+

33.3
10.8
20.0
3.2
1.8
14.8
15.6

Outer

34.2
33.3
23.4
17 .9
19.6
24.1
18.5
4.0
4.6
2.5
0

C

97.4

100
32.4
60.1
9.6
5.4
44.4
46.8

100
97.4
68.4
52.3
57.3
70.5
54.1
11.7
13.5
7 .3
0

D

~

B

4
4

4
4

4
4

4
4

4

4

4
4

3

2

4

2
4

2

3

2

4

4

+

42.8, 49.0
17.2, 18.9
27.8, 33.4
2.1, 2.5
0.8, 2.4
20.5, 25.2
18.4, 20.5

Outer

47.7, 50.5
42.3, 46.0
32.5, 36.6
25.6, 28.8
28.5, 31.1
34.9, 38.3
21.6, 24.5
6.5, 7.7
6.2, 10.2
2.0, 2.3
2.1, 8.0

c

45.4
40.1
67.6
5.0
4.1
49.1
42.1

4.3
12.8

46.3
14.1

55.6

49.5
90.3

E

86.7, 98.5 91.9

100
38.6, 42.1
64.7, 70.9
4.6, 5.4
1.6, 5.6
42.5, 58.7
41.1, 43.0

100
88.7, 90.9
68.1, 72.5
53.7, 58.0
59.7, 61.8
73.2, 75.8
43.5, 49.3
13.3, 15.2
12.9, 20.2
4.0, 4.8
4.2, 16.1

D

30
Pseudorca crassidens

29

Sousa teuszii

7

7

7

6

6

7
7

7

6

7

7

7

6

5

7

7

6
6

6

5

7

7

B

APPENDIX II.

+

73.6, 87.5
30.0, 36.0
46.8, 57.3
1.2, 3.2
1.9, 5.2
33.1, 46.3
25.8, 32.6

0
Outer

70.2, 85.0
62.1, 76.0
50.3, 62.7
38.5, 46.9
39.8, 49.4
50.9, 63.7
34.7, 46.9
7.6, 16.1
7.3, 10.9
2.2, 3.8

c

79.8
42.1
65.3
3.1
4.6
48.0
34.6

Closed

79.2
87.2
71.6
53.6
56.1
71.8
51.5
15.6
12.3
4.2

E

94.0, 105.0 100.9

10038.0, 48.6
53.5, 70.8
1.4, 7.9
2.2, 6.1
43.5, 62.6
31.8, 38.6

0100
83.8, 90.8
68.2, 74.5
49.6, 55.8
52.5, 58.8
67.3, 75.8
47.3, 55.8
10.8, 19.8
9.5, 13.8
3.2, 4.9

D

Orcinus area

31

Continued.

6

6

6
6

6
6
3

6
6
6
6
6
6
6

6
6
6

6

6
6

6

6

B

32

+

30.8, 34.2
13.5, 15.7
21.3, 22.8
0.4, 1.2
0.4, 1.9
14.5, 16.0
14.2, 15.9

Outer

34.0, 37.9
30.3, 33.8
25.4, 26.7
19.2, 20.9
19.1, 20.6
26.8, 28.1
16.0, 18.1
4.7, 5.3
4.7, 6.0
1.0, 1.7
4.0, 5.2

C

32.l
45.0
67.8
2.4
3.0
49.3
46.3

35.9
89.8
71.8
56.1
55.3
75.7
47.5
13.9
14.6
3.6
12.5

E

81.3, 93.8 89.5

100
40.6, 48.9
65.5, 69.8
1.6, 3.9
1.2, 5.6
45.4, 51.9
43.8, 49.0

100
88.1, 93.4
67.0, 73.7
53.6, 58.3
50.4, 58.9
69.7, 80.3
42.2, 53.2
12.6, 15.6
12.9, 17.6
2.7, 4.0
9.7, 14.7

D

Peponocephala electra

><

"'°

<O

"'

~f:zj

O:I

0

~.....

~

0

~

~

"1

~

.:-

~ ·~

£;; ·~.......

.~~""

~

~

~

~-

·c.,

7

7

7

7

7

7

.7
7
7
7
7
7
7
7
7
7
7
7
7

4

5

6

7

8

9

20

22

21

2.8

+
86.5, 94.0

100
40.2, 46.2
63.0, 73.5
2.6, 6.5
3.3, 6.3
35.9, 49.3
37.6, 45.6** Closed on 25

Outer
35.3, 37.8
15.1, 16.4
23.3, 27.2
0.9, 2.4
1.2, 2.3
12.9, 17.4
13.8, 16.6

0 '

D

100
84.5, 90.5
71.0, 73.5
51. 7, 55.4
50.6, 57.5
73.5, 77.6
42.6, 49.6
11.3, 16.1
13.1, 17.6
1.8, 6.7
0 ' 6.9

c
E

90.2

36.3
43.l
70.3
4.8
5.3
40.4
41.9

40.3
87.6
72.5
53.7
53.5
75.9
46.1
13.5
15.1
3.0
1.5*

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

4

B

+

Outer
36.8, 43.4
16.7, 23.9
23.0, 25.0
1. 2, 3.0
0.2, 1.5
14.9, 22.4
16.5, 17.6

79.7, 87.5

100
41.2, 64.9
57.6, 64.5
3.3, 8.1
0.5, 3.8
4.0.1, 52.4
40.0, 45.8

0

0

D

100
83.0, 85.5
64.2, 69.0
47.6, 52.9
46.8, 51.3
67.3, 71.6
40.7, 43.8
9.3, 11.0
11.9, 18.1
3.1, 3. 7

46.2, 49.7
37.6, 42.5
30 .1, 31.9
23.3, 23.9
21.7, 23.2
31.1, 33.9
18.8, 20.4
4.2, 5.1
5.9, 8.2
1.4, 1.8c34Globicephala melaena

33

Feresa attenuata

39.3, 41.2
33.5, 36.4
28.2, 29.8
. 20.3,. 22.2
20.8, 22.6
29.4, 31.8
17.5, 19.6
4.5, 6.4
5.4, 7.1
0.4, 2.7* Closed on 5

7

7

2
3

10
11
12
13
14
15
16
17
18
19

7

B

I

A

APPENDIX II. Continued.

E

83.8

39.1
52.0
61.6
4.6
2.5
47.2
44.0

46.7
84.4
66.6
50.7
48.9
69.2
42.1
10.0
15.0
3.4
Closed

B

26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26
26

35

+

0 ' 1.3
Outer
33.2, 39.5
14.7, 22.8
22.2, 26.5
0.4, 2.3
0.3, 3.5
12.6, 25.1
14.5, 17.8

36.4, 52.1
34.2, 44.1
26.8, 30.3
19.6, 22.9
19.2, 23.5
28. 2, 32.1
15.8, 21.0
2.9, 5.4
4.9, 8.1
0.8, 2.4c69.2, 94.8

43.1, 60.8
58.0, 74.6
1.1, 6.5
0.8, 10.2
37.0, 74.8
41.9, 50.9 .

100

100
79.6, 98.0
52.1, 73.6
38.8, 53.3
42.4, 55.5
58.5, 82.7
37.6, 50.3
7.1, 12.3
11.0, 18.0
2.5, 5.7
0 ' 3.1

D

Globicephala macrorhyncha
E

82.0

35.7
49.2
68.8
4.0
4.4
48.5
45.6

3.8
0.1**

43.7
88.4
65.9
48. 7
49.8
70.0
43.1
10.0
14.8

~

~

~
>

:12

~~

"'

!:;'<

~

"'~

. "'~

~ ;§

""~
·""......
~

?'.
~
~ r"·

12
11

11

12
12
12
12
12
12
12
12
12
12
12

4

5

6

7

12
13
14
15
16
17
18
19
20
21
22

11

* Closed on 11

12
12
12
12

+

11

2

3

11

38.7, 46.8
31.8, 39.9
27.6, 30.8
20.8, 24.0
19.0, 23.9
28.5, 31.0
16.5, 22.0
2.7, 6.7
4.9, 9.2
0.7, 2.0
0 , 4.0
Outer
34.8, 45.2
11. 7, 25.0
23.6, 28.0
0.5, 2.7
0.8, 3.5
13.4, 18.4
15.4, 18.5

12
12

8
9
10

c

86.6, 100.0

10031.1, 55.3
56.0, 75.9
1.3, 7.1
1.8, 7.2
34.3, 47.5
37.0, 48.9

100
76.5, 88.9
62.4, 75.4
46.8, 58.6
43.8, 58.7
64.8, 78.l
36.1, 52. l
6.1, 14.3
12.1, 20.2
1.8, 5.1
0 , 9.9

D

E

/

92.4

38.5
43.4
67.3
4.3
4.1
40.9
43.3

0. 7*

41.9
34.2
70.1
53.l
50.1
72.8
43.8
10.3
15.8
3.0

2

2

2

2

1

2

2

2

2

2

2

2

2

l

2

2

2

2

2

2

B

+

Outer
34.3, 40.7
12.7
20.5, 21.2
0.9, 1.4
1.7, 2.0
17.0
15. l, 15. 2

036.9, 39.2
34.5, 37.5
24.l, 24.7
16.0, 17.4
20.0, 21.2
26.5, 26.8
18.7, 21.5
3.2, 4.3
3.9
1.9, 3.8cD

93.0, 103.8

93.0, 103.8
31.2, 37.0
52.1, 59.8
2;2, 4.1
4.2, 5.8
49.6
37.3, 44.0

0100
93.5, 96.3
63.0
42.9, 45.6
52.0, 57.5
67.6, 70.0
50.7, 55.0
8.2, 11.7
10.0, 10.2
5.1, 9. 7

37
Orcaella brevirostris

36

Grampus griseus

B

A

APPENDIX II. Continued.

4

4

4

4

3

3

3

3

4

+

Outer
37.7, 40.4
13.9, 16.2
26.4, 27.4
1.2, 2.8
2.5, 3.1
16.8, 21.4
19.2, 20.3

4
4

0

87.6, 94.5

100
36.9, 42.2
65.3, 72.8
3.0, 7.3
6.2, 8.1
44.6, 53.0
47.0, 52.9

90.4

39.0
39.4
69.5
5.0
7.4
48.9
49.9

E

42.9
96.6
78.9
57.0
58.9
80.4
48.8
15.1
15.6
10.8
ClosedD

100
93.0, 98.4
78.4, 79.3
54.2, 61.2
58.0, 59.0
80.3, 80.4
47.8, 49.8
14.2, 16.1
14.8, 16.3
10.l, 11.8
0c40.7, 45.0
39.7, 42.7
32.2, 33.1
24. l, 24.9
24.0, 26.0
32.7, 33.9
20.0, 21.5
6.1, 6.8
6.0, 6.9
4.1, 5.3

4

3

2

4

4

2

3

4

2

4

4

B

38
Delphinapterus leucas

~

trj
Cl'

z

0

0
b:!

Q
.....

~

~0

~

~

;::l ~~

~~

~
.~~"'
...""~
u-a ?:

~

~

~

B

c
D

83.5

42.3
53.2
66.5
4.8
7.4
63.3
45.2

E
50.7
87.2
74.8
53.7
39.6
73.7
44.0
13.9
15.0
7.5
1.5*

5

5
5
5
5
5
5
5
5
5
4
5
5
5
5
5
5
5
5
5
5
5

B

c

+

63.1, 70.4
50.3, 61.2
47.0, 53.1
35.3, 40.8
38.7, 45.5
46.0, 51.2
33.6, 40. l
1.4, 3.8
18.8, 21.0
5.9, 6.5
0 ' 14.5
Outer
66.9, 75.8'
29.0, 38.1
34.7, 37.2
0.8, 4.8
1.9, 5.1
23.4, 26.0
23.2, 25.l

101.0, 113.4

100
43.4, 50.3
49.6, 54.1
1.2, 6.9
2.8_7.4
31.4, 37 .1
33.1, 37.5

0 ' 20.9

100
78.9, 84.6
72.6, 76.7
54.3, 58.8
57.1, 67.7
70.0, 73.6
52.6, 57.0
21.4, 5.4
29.0, 31.4
9.1, 9.6

D

40
Berardius bairdi

39

Continued.

Monodon monoceros

4100
50.1, 50.9
2442.8, 46.2
84.4, 90.8
34
36.8, 39.0
72.5, 76.6
44
26.0, 27.8
51.3, 55.5
45
19.0, 20.9
37.5, 41.4
6
4
36.3, 38.6
71.6, 76.0
7
4
20.8, 23.8
40.8, 46.8
84
6.3, 7 .8
12.4, 15.3
94
7 .1, 8.1
14.0, 15.9
410
2.0, 4.9
5.2, 9.7
4
11
3.1
0 ' 6.1
0 '
12
4
Outer
13
4
37.0, 49.4
100
144
20.4, 23.5
41.3, 59.7
4
15
25.4, 30.9
62.7, 68.8
416
2.0, 3.1
4.1, 6.2
17
4
2.5, 4.1
5.5, 9.5
184
25.5, 27.7
51.3, 68.4
194
17.2, 20.9
40.1" 48.6
4
20
+
21
4
22
4
73.6, 98.6
* Closed on 3** Closed on 1

A

APPENDIX II.

106.6

71.0
46.9
51. 7
3.1
4.9
33.3
34.5

E
66.7
81.0
74.7
57.2
64.3
71.9
54.5
4.7
29.7
9.3
5.9**

1

+

0
18.8

1
1

c
63.2
47.5
47.4
36.2
44.1
45.0
36.5
3.3
21.6

1
1
1
1
1
1
1
1
1

B

41
B. arnouxii
D

0
29.8

100
75.0
75.3
57.2
69.8
71.2
58.0
5.2
30.2

42

I

1

1

I

1
1
1
1
1
1

+

Outer
61. l
20.3
33.0
0.5
1.5
25.2
23.0

16.5

1

c
54.5
47.3

1
1

B

112.0

100
33.2
54.0
0.8
2.5
41.2
37.6

30.3

100
86.8

D

Hyperoodon ampullatus

~

c:::

~

>
fJJ

~

<.O

!""·

~
~[

"'

~~.,.

....

""::>::i
Yi~

~

~~

2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

1

A

+

-

44.3, 50.9
16.4, 18.3
26.9, 29.1
0.2, I. 7
2.6, 3.3
15.4, 17.7
19.0, 20.9

92.8, 104.0

33.4, 41.3
56.9, 61.3
0.4, 3.3
5.5, 6.5
34.8, 41.6
40.3, 43.0

JOO

100
88.8, 97.5
69.0, 74.9
52.8, 56.6
67.0, 70.2
78.5, 82.0
48.2, 55.8
5.2, 9.1
31.4, 34.8
7.6, 13.0
13.2, 17 .6

46.9, 49.0
42.2, 47.2
33.0, 35. l
25.3, 27.0
27.8, 33.9
37.8, 39.2
23.1, 27.0
2.5, 4.4
14.8, 16.6
3. 7, 6.r
6.1, 8.4

7
7
6
6
5
5
7
7
6
3
7
7
4
4
4
4
4
4
4
4
4
4

Outer

D

c·

B

E

98.8

47.5
37.0
59.2
I. 7
6.1
37.5
41.5

47.7
94.8
72.0
54. l
67.1
80.5
50.8
7.2
32.2
8.2
10.5
-1Outer

4
4
l
l
l
l
l
l
l
4
4
I

+

-

52.2
20.1
28.0
1.4
4.3
16.9
22.0

49.7, 54.2
47.0, 49.5
36. l, 38.4
29.4
32. l
39.8, 42.7
22.9, 28.3
I. 7, 4.0
15.3, 17.2

c

4
4
3
I
1
3
4
4
3

B

96.3

100
38.5
53.6
2.7
8.2
32.4
42.1

+

100
90.0, 95.6
72.5, 73.5
54.2
59.2
72.1, 80.5
45.7, 52.2
3.1, 8.1
30.5, 34.6

D

44
M. densirostris43

Mesoplodon stejnegeri

APPENDIX II . Continued.

75.3
49.2
6.3
32.0

51.8
93.4
72.9

E

2
2
2
I
2
2
2
2
2
I
2
2
2
2
2
2
2
2
2
2
2
2

B

45

+

41.0, 42.3
20.4, 20.6
22.3, 23.1
0 ' 0.4
2.2, 3.0
13.8, 15.4
16.0, 17 .8

Outer

+

39.8, 44.l
37.4, 41.6
30.3, 34.l
24.7
28.0, 30.4
31.6, 35.2
20.3, 28.5
I. 7, 3.5
14.0, 15.6
2.9

c

>--l
......

96.0, 103.0

100
48.2, 50.2
54.4, 54.6
0 ' 0.9
5.4, 7. I
32.6, 37.6
39.0, 42.1

0

+

__,

<O

rFJ

ztr:I

0

l:d

~
tr:I
:;tl

~0

~

......

-<:

>--l

0

D

100
94.0, 94.5
76. l, 77 .3
56.0
69.0, 70.4
79.4, 79.9
51.0, 64.6
4.3, 7 .9
35.2, 35.4
6.6

M. ginkgodens

~-=

~~

~Ll-\ ~"° ::c

.~~
"'

~

~

~
::c

12
13
14
15
16
17
18
19
20
21
22

11

l
2
3
4
5
6
7
8
9
10

A

1
1
1
1
1
1
3
3
1

I

+

-

44.5
18.5
25.0
0
2.8
16.7
16.0

Outer

+

3
3

3

l

41.1, 45.7
38.4, 43.2
34.2, 35.5
25.8, 26.5
30.3
34.8, 38.7
23.4, 23.9
3.3
13.8, 16.9

0

97.5

I

100
41.6
56.2
0
6.3
37 .6
36.0
1
1

I

I

1
1
1

I

1

1
1

34.1

l

83.0
55.0
2
1
1

2
2
l
l
l

44.l
94. l
79.5
59.6

B

+

100
93.4, 95.0
75.0, 86.4
56.8, 64.5
66.3
79.3, 85.0
52.5, 57.0
7.2
32. 2, 37. 1

E

+

-

49.4
20.9
17.6
0.8
1.9
17.7
20.0

Outer

7.5

48.4, 49.4
46.2, 46.8
34.6
21.8
31.9
40.6
27.4, 28.7
3.8
14.8

100.0

100
41.9
35.6
1.6
3.8
35.8
40.4

15.2

100
94.7, 95.5
71.5
44. l
65.9
83.9
56.6, 58.l
7.7
30.6

D

1

I

I

1

l
1
1

l

l
l
l
l
l

B

+

-

Outer

8.7

41.0
37 .1
32.7
23.8
25.8
35.2
20.8
13.9
15.6

c

21.2

100
90.5
79.5
58.0
63.0
86.0
50.8
9.5
38.0

D

,..------''---------._

.C

D

c

3
3
3
3
l
3
3

B

48
M. mirus

47
M. carlhubbsi

46

Continued.

Mesoplodon europaeus

APPENDIX II.

6
5
6
5
6
6
5
5
6
2
7
7
7
7
7
7
7
7
7
7
7
6

B

c

+

51.8, 59.7
43.8, 50.l
41.9, 44.3
32.6, 36.3
27.0, 37.6
38.6, 44.8
21.2, 26.0
1.0, 2.4
15.1, 17 .8
2.1, 2.2+

54.0, 62.4
22.3, 27.0
29.5, 34.1
0.4, 3.8
1.2, 5.6
20.5, 23.8
18.8, 22.6

Outer

49
E

57 .6
41. 7
55. l
3.7
6.8
38.2
36.6

55.9
87.8
77.3
61. 7
61.3
76.4
41.6
3.0
29.6

92.5, 116.0 103.6

100
38.5, 45.0
50.0, 58.0
1.6, 6.9
2.1, 10.4
36.0, 39.6
33.6, 40.1+

100
83.0, 93.3
72.4, 81.0
56.5, 66.4
52.1, 64.9
72.8, 77 .9
38.6, 50.2
1.8, 4.6
25.3, 31.7
3.8, 4.0

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5

4

4

4

3

4

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12
13
14
15
16
17
18
19
20
21
22

4

4

24.0, 30.5
8.5, 11.5
18.0, 20.9
0 .5, 1.0
2.2, 3.8
12.6, 16.0
12. 7, 14.4

5

11

83.4, 109.3

100
29.2, 47.9
59. 7, 87 .0
1.6, 3.9
7 .2, 15.6
45.2, 61.8
41.6, 58.4

3

4

10
0

2
4

0

Outer~Inner

5

7

8
9

93.6

26.2
40.8
77 .0
2.9
10.9
53.8
53.1

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31.6
4.1

61.3

3

88.4

4

6

3

4

5

2

4

4

4

3

4

4

4

4

3

2

3

2

3

2

78.5
54.0
50.4

4

3
3

77.0

5

3

B

4

5

2

E

30.1

D

100
61.0, 85.5
76.3, 81.0
50.3, 56.5
46.0, 56.3
84.6, 93.2
48.1, 66.5
4.1, 6.8
27.8, 37.6
1.8, 5.7c26.2, 38.5
20.8, 24.1
21.2, 22.5
14.0, 16.5
12.0, 15.7
23.6, 26.2
17.4, 18.5
1.2, 1.9
7.8, 10.5
0.5, 1.5

B50
K ogia breviceps

3
4

A

+

0 ' 1.0
1.8, 2.7
11.6, 13.9
11.0, 12.8

22.7, 29.2
8.2, 11.4
17 .0, 19.2

Outer~Inner024.2, 27.5
18.5, 25.0
19.9, 21.9
12.8, 14.5
14.3, 16.4
22.9, 23.9
14.4, 18.4
1.2, 2.1
7.4, 9.3
0.7, 1.8

c106.2, 109.1

0 ' 3.9
6.4, 9. 7
41.4, 49.6
41. 7, 53.4

100
31.1, 40.6
63.0, 75.5

0100
89.8, 94.2
74.0, 84.7
47.6, 52.9
53.5, 66.1
85 .1, 97 .5
52.4, 64.9
6.5, 8.7
27.6, 33.8
2.9, 6.5

D

Continued.

51
K. simus

APPENDIX II.

E

8.2
46.2
46.1

0 in 3

26.6
36.6
68.7

Closed

31.6

59. 7
89.8
60.1

26.2
92.3
79.4

8
8
8
8

7

8

8
8
8
8

8
8
8
8

7

7

8

8

7
6

8

8

B

c

0

+

0. 7, 3.0
24.3, 30.1
23.2, 28.8

057.7, 68.9
32.2, 36.8
34.2, 42.1

Inuer

55.4, 62.8
45.5, 57.1
41.2, 44.4
30.1, 34.3
33.4, 39.5
47.7, 51.8
24.1, 27.7
1.5, 2.9
25.5, 28.2

E

3.2
42.1
41. 7

0

63.6
54.0
59.3

Closed

59.8
84.2
71.1
53.6
59.6
79.1
42.8
3.4
45.4

94.1, 116.5 106.7

1.2, 4.6
37.6, 46.6
36.0, 45.9

0100
50.2, 60.3
53.0, 64.6

0100
75.8, 91.2
68.3, 75.5
50.2, 56.9
37.0, 66.5
77 .1, 87 .2
38.4, 46.2
2.5, 4.9
41.6, 48.9

D

52
Physeter catodon

tD
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100

KASUYA

EXPLANATION OF PLATESPLATE I
Posterior process of tympanic bulla and that of periotic, and their connection with theskull. BO, Basioccipital. EO, Exoccipiral. P, Periotic, PPP, Posterior process of periotic.
PPT, Posterior process of tympanic bulla. SQ, Laminated portion of squamosal. T, Tympanic bulla.
Fig. 1. Physeter catodon, TK85, ferns, skull length 75 cm, ventro-lateral view, righr side.
Fig. 2. Physeter catodon, TK165, 5.0 m female, skull length 115 cm, same view.
Fig. 3. Physeter catodon, TK261, adult female, same view.
Fig. 4. Mesoplodon densirostris, TK256, 356 cm female, postero-lateral view, left side.
Fig. 5. Kogia breviceps, TK244, 197 cm female, postero-ventral view, right side.
Fig. 6. Platanista gangetica, TK363, 122 cm (juvenile) male, same view.
Fig. 7. Platanisatagangetica, TK 357, 200 cm male, ventral view of skull and periotic. Dotted
area indicates the facet for posterior process of tympanic bu!Ia.
Fig. 8. Delphinapterus leucas, SDNHM20046, ventral view, right side.
Fig. 9. Balaenoptera borealis, fetus, lateral view of right tympano-periotic bone.
PLATE II:(,iphius cavirostris, TK296, tympano-periotic bone, left side.
PLATE IIITympano-periotic bones.
Figs. 1-10. Berardius bairdi, TK299, right side.
Figs. 11-13. Mesoplodon mirus, AMNHl 74293, right side.
Two black spots on Fig. 8 are artific'al and insignificant.
PLATE IV
Tympano-periotic bones.
Figs. 1- 9. Mesoplodon stejnegeri, TK97, right side.
Figs. 10-16. Hyperoodon ampullatus, USNM14449, left side.
Figs. 17-20. Berardius arnouxi, USNM21511, left side.
PLATE V
Tympano-periotic bones.
Figs. 1-10. Mesoplodon densirostris, TK256, 356 cm female, right side.
Figs. 11-16. Mesoplodon europaeus, USNM306302, right side.
PLATE VI
Tympano-periotic bones.
Figs. 1-10. Mesoplodon ginkgodens, HCY specimen, left side.
Figs. 11-18. Mesoplodon carlhubbsi, USNM274591, right side.
PLATE VII
Tympano-periotic bones.
Figs. 1-10. Physeter catodon, NUMS specimen, left side.
Physeter catodon, TK304, left side.
Fig. 11.

Sci. Rep. Whales Res. Inst.,
No. 25, 197!1.

101

TYMPANO-PERIOTIC BONES
PLATE VIII
Tympano-periotic bones.
Figs. 1- 9. Kogia simus, TK47, 245 cm, right side.
Figs. 10-18. Kogia breviceps, TK244, 197 cm female, left side.
Figs. 10-18. Kogia breviceps, TK244, 197 cm female, left side.
posterior process of tympanic bulla is removed.

In Figs. 5 and 14, part of

PLATE IX
Tympano-periotic bones.
Figs. 1-11. Platanista gangetica, TK357, 200 cm male, left aide.
Figs. 12-13. Platanista gangetica, TK351, 171.5 cm male, right side, showing the ossicles
attaching to anterior process of periotic.
Figs. 14-23. Pontoporia blainvillei, USNM49494 right side.
PLATE X
Tympano-periotic bones.
Figs. 1- 8. lnia geoffrensis, LACM19589, left side.
Figs. 9-15. Inia geoffrensis, LACM19590, left side.
Figs. 16-20. Lipotes vexillifer, AMNH57333, left side.
PLATE XI
Tympano-periotic bones.
Figs. 1-10. Orcaella brevirostris, USNM199743, left side.
Figs. 11-13. Orcaella brevirostris, ZSI 274, right side.
Figs. 14-20. Delphinapterus leucas, AMNH180017, right side.
PLATE XII
Tympano-periotic bones, shadow lines on the tympanic bullae indicate contour lines.
Figs. 1- 9. Neophocaena phocaenoides, TK95, right side.
Figs. 10-18. Phocoena phocoena phocoena, TK84, left side.
PLATE XIII
Tympano-periotic bones, shadow lines on the tympanic bullae indicate contour lines.
Figs. 1- 9. Phocoenoides truei, TKI 13, right side.
Figs. 10-18. Phocoenoides dalli, TK129, 186 cm female, left side.
PLATE XIV
Tympano-periotic bones.
Figs. 1-13. Sousa teuszii, TK260, 191 cm female, left side.
Figs. 14-20. Cephalorhynchus sp. USNM252568, left side.
PLATE XV
Tympano-periotic bones.
Figs. 1- 8. Sotalia guianensis, CNHM 34907, left side.
Figs. 9-12. Sotaliajluviatilis, AMNH94169, left side.
Figs. 13-15. Tursiops gilli, SDNHM20144, right side.

Sci. Rep. Whales Res. Inst.,
No. 25, 1973.

102

KASUYA
PLATE XVI
Tympano-periotic bones.
Figs. 1- 9. Tursiops truncatus, 292 cm male, right side, from the coast of Japan.
Figs. 10-14. Tursiops truncatus, 335 cm male, right side, same locality.
PLATE XVII
Tympano-periotic bones.
Figs. 1- 8. Stene/la caeruleoalba, adult, right side.
Fig. 9.
Stene/la caeruleoalba, 92 cm male, fetus, left side.
Fig. 10.
Stenella caeruleoalba, adult, right side.
Figs. 11-18. Stenella attenuata, TK103, right side, from the coast of Japan.
Fig. 19.
Stene/la attenuata, TK60, right side, same locality.
Stenella attenuata, TK61, left side, same locality.
Fig. 20.
PLATE XVIII
Tympano-periotic bones.
Figs. 1- 9. Stene/la grajfmani, WAW44, 179 cm female, left side, l2°08'N, l05°46'W.
Figs. 10-12. Stenella sryx, left side, from the north Atlantic.
PLATE XIX
Tympano-periotic bones.
Figs. 1- 8. (?)Stene/la roseiventris (Hawaiian spinner dolphin), TK50, 180 cm male, left side.
Figs. 9-10. (?) Stenella roseiventris (Hawaiian spinner dolphin), TK295, 195 cm male, left
side, from Hawaii.
Figs. 11-19. (?) Stenella longirostris, WAW52, 168 cm male, left side, 21°06'N, 106°16'W.
PLATE XX
Tympano-periotic bones.
Figs. 1- 9. Lissodelphis borealis, TK257, 245 cm male, left side.
Figs. 10-11. Lissodelphis borealis, TK258, 224 cm female, right side.
Figs. 12-19. Delphinus bairdi, TK255, 204 cm female, right side, from Formosa.
PLATE XXI
Tympano-periotic bones.
Figs. 1- 8. Delphinus delphis, TK specimen, left side, from the north Atlantic,
Figs. 9-16. Lagenorhynchus obliquidens, TK229, left side.
Figs. 17-19. Lagenorhynchus obliquidens, TK230, left side.
PLATE XXII
Tympano-periotic bones.
Figs. 1- 8. Lagenorhynchus acutus, USNM14265, right side.
F!gs. 9-11. Lagenorhynchs obsculus, AMNH34935, left side.
Figs. 12-17. Lagenorhynchus amtralis, CNHM22248, left side.
PLATE XXIII
Tympano-periotic bones.
Figs. 1- 9. Lagenorhynchus albirostris, TK87, left side.
Figs. 10-18. Steno bredanensis, TK73, left side.

Sci. Rep. Whales Res. Inst.,

No. 25, 1973.

TYMPANO-PERIOTIC BONES
PLATE XXIV
Tympano-periotic bones.
Figs. 1-13. Pseudarca crassidens, TK specimen, left ~ide.
Figs. 14-17. Oreinus area, TK specimen, left side, (continue to Pl. XXV).
PLATE XXV
Tympano-periotic bones.
Figs. I- 2. Oreinus area, TK specimen (continued from Pl. XXIV).
Figs. 3-15. Pepanaeephala eleetra, TK32, left side.
PLATE XXVI
Tympano-periotic bones.
Figs. 1-10. Feresa attenuata, TK27, 214 cm male, left side.
Figs. 11-19. Grampus griseus, TKIOI, left side.
Figs. 20-22. Grampus griseus, TK specimen, left side.
PLATE XXVII
Tympano-periolic bones.
Figs. 1-11. Glabieephala melaena, TK specimen, left side, from the north Atlantic.
Figs. 12-20. Glabieephala maerarhyneha, TK287, 358 cm female, left side.
Figs. 21-22. Glabicephala maerarhyneha, TK292, 203 cm female, right side.
Figs. 23-24. Glabicephala maerarhyneha, TK291, 141 cm male, left side.
PLATE XXVIII
Tympano-periotic bones.
Figs. 1-10. Manadon manaeeras, SDNHM7096, right side.
Figs. 11-13. Manadan monaeeras, AMNH73318, left side.

Sei. Rep. Whales Res. Inst.,
No. 25, 1973.

103

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