AGE DETERMINATION, REPRODUCTION, AND
GROWTH OF THE FRANCISCANA DOLPHIN,
PONTOPORIA BLAINVILLEITOSHIO KASUYA
Ocean Research Institute, University of Tokyo, TokyoAND
ROBERT L. BROWNELL, JR.
National Fish and Wildlife Laboratory, National lviuseumof Natural Histor_v, Washington, D.C. 20560

ABSTRACTAn examination was made of 260 Franciscana dolphins taken off the
Uruguayan coast. Deposition of dentinal and cementa! layers is annualwith the formation of an unstainable layer between August and November.
Cementum deposition continues after the probable cessation of dentine deposition at four to seven years. Females usually have a 2-year reproductive cycle.
Calves are born at a length from 70 to 75 cm after a gestation of about 10.5
months, and weaned before one year of age. Sexual maturity is attained inboth sexes at an age between two and three years, which corresponds to thelength of 131 cm and weight of 25 to 29 kg in males, and to 140 cm and 33
to 34 kg in females. Physical maturity is attained soon after the onset of
sexual maturity. Sex ratio is at parity in immature individuals.
INTRODUCTION

The Franciscana dolphin Pontoporia blainvillei (Gervais and d'Orbigny, 1844) inhabits the coastal waters off eastern South America from Valdes Peninsula (42°30'S ),Argentina, north to the Tropic of Capricorn near Ubatuba, Brazil (Ximenez,
Langguth, and Praderi, 1972).
The purpose of this study was to investigate reproductive parameters andgrowth in this species. Specific objectives included collection and analysis of
information on age of sexual maturity, frequency and timing of calving, growth,and sex and age composition.
MATERIALS AND METHODS

The dolphins examined in this study, 123 females and 137 males, were collected
dead, offshore from Punta del Diablo, Uruguay, by local fishermen in gillnets set
for sharks. Details on the fishing methods used at Punta del Diablo are given
by Van Erp (1969), Brownell and Ness (1970), Pilleri (1971), and Brownell (1975).
Sci. Rep. Whales Res. Inst.,
No. 31, 1979, 45-67

46

KASUYA A"'.\'D BROWNELL

Ma.le

25
20

15
<ll

~

10

"O

·:;;
"O

5

c

Female

0

z

15
10

5
ou.....1--...-~'r'-""1"''IL''IL'-..U~~~~~~~..._i..-i~=-

eo

so

100

110

120

130

140

1so

1so

110

Body length in cm
Fig. 1. Body length frequency of Pontoporia blaiiwillei. Right column (black) represents the random sample cited from Brownell (1975), left column the present
material, and shaded area individuals of unknown age.
TABLE 1.

MATERIALS OF PONTOPORIA BLAINVILLEI USED IN THIS STUDY

Month
Male 1>
2)

Female1>
2)

Female, %'>79 3 >
0
57 3 >
0
41.9

II

III

VI

VII

VIII

3
0
7
0
'70.0

2
0
3
0
60.0

3
0
3
0
50.0

1
7
0
0
0.0
0.0

3

,, '%2)
1>:

Random s:imple,

2>:

4
25.0
80.0

IX
1
2
3
66.7
75.0

x
0
2
6
66.7
100.0

XI

XII

Total

0
1
2
6

33

126
11
98
25
43.8
69.4

rno.o
85.7

21
6
38.9
85.7

3

Nonrandom sample, >: One aged individual of unknown length included.

Over 400 dolphins were collected by us or a local fisherman Amilcar Olivera (AO)
between December 1970 and December 1973. The sample was heavily biased
toward December and January (austral summer), because of the seasonal natureof the shark fishery, with minimal coverage during the rest of the year. The bodyweight and external proportion data were obtained from specimens taken between
December 1972 and January 1973. The standard total length of each specimen
was measured in a straight line from the tip of the rostrum to the notch in the
flukes. The material we collected was a random sample of the catch, but the AO
specimens are biased towards adult females exceeding 135 cm in total length.
Olivera only agreed to collect a limited number of specimens. Therefore, we
asked him, in our absence, to collect all adult females landed.

Tooth preparation
Although the anterior teeth are slightly longer than the others, the difference
is not as extreme as in Platanista. Three to five contiguous mandibular teeth,
Sci. Rep. Whales Res. Inst.,

N1J. 31, 1979

FRANCISCANA DOLPHIN

47

starting at approximately the tenth from the front and moving posteriorly, werecollected and fixed in 10% formalin solution or 70% ethanol.
The principle of the preparation is to decalcify and stain a thin longitudinalground section glued with cyanoacrylate monomer on a clear plastic plate (Kasuya,1978). The tooth was ground down to a thickness of 20 to 30 µm. The decalcification was done with 5% formic acid for several hours at about 25°C. The
slide was then rinsed in running water for two hours or longer, stained with Mayer's
haematoxylin for 30 minutes, and finally mounted with Canadian balsam. Bothanterio-posterior and lingual-buccal sections were prepared for most individuals;
they were not significantly different in readability. However, since the teeth arecompressed anterior-posteriorly, the chance of missing the pulp cavity is less inthe anterio-posterior section.
Reading of growth layers
The age determination was based on the growth layers in the dentine andcementum. Observations of growth layers were made with a compound microscope (40 to 120 X ), without referring to the biological data. At first, about 20
slides, probably representing new born individuals and very old individuals, wereselected, and the standard of reading was established by comparing the growthstage and layer counts of the slides. Then all the slides were read by the same
standard. If the number of cemental layers exceeded significantly that in dentine,
the former was taken as the age. This only occurred when teeth had narrow pulp
cav1t1es. In cases where the counts of dentine and of cementa! layers differed
only by a fraction of a layer, the dentine count was taken as the age because it isclearer and more reliable than the cementa! layer. If the independent readingsof the growth layers in the same tissue of two slides from one individual were different, they were carefully compared including the difference of the finish, and thena final decision was made without referring to the biological data. When there wasno choice in the interpretation of the fraction of the last incomplete layer, themean of the two counts was used.
One complete growth cycle was considered to be composed of one broadstainable layer and a narrow unstainable layer. The final fractional layer was
estimated by eye to the nearest 0.1 layer. Although this is not highly accurate, it
gives a better result when the sample is seasonally biased.

AGE DETERMINATION
Morphology and number ef teeth
The number of teeth ranges from 48 to 61 on each tooth row (Table 2).
There are no consistent sexual or bilateral differences. However, the number ofteeth is significantly different between the upper and lower jaws (p<0.001).
The excess of upper teeth over the lower varies from -1 to + 11 with a mean of
3.3 in females, and from -1 to +9 with a mean of 2.7 in males. This is related
to the downward curving of the rostrum. In Platanista gangetica, the rostrum isSci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND BROWNELL

48

curved upward and the number of lower teeth exceeds the upper (Kasuya, 1973).
The straight length of a tooth is approximately 7 to 10 mm. The pointed
crown is compressed anterio-posteriorly and the tip is curved mesially. The rootis flattened lingual-buccally and the proximal tip is usually curved, through thegrowth, towards the posterior direction. The cementum forms a thick cingulum
at the cervix of the tooth. In old individuals the root is covered by the cementum
leaving small branching canals connecting the narrow pulp cavity and externalsurface of cementum. (Pl. IV, Fig. 1).
TABLE 2.
Position
Male
Up. left
Up. right
Lo. left
Lo. right
FemaleUp. left
Up. right
Lo. left
Lo. right

TOOTH COUNT OF PONTOPORIA BLAINVILLEI

Sample

Range

Mean

SD

SE

3·3
33
33
32

51-60
51-60
48-61
49-59

54.6
55.0
53.3
53.4

2.25
2.24
2.54
2.33

0.39
0.39
0.44
0.41

39
39
38
38

50-60
50-61
49-58
49-59

55.4
55.3
53.7
53.6

2.62
2.67
2.2li
2.40

0.42
0.43
0.37
0.39

Growth layers
When a thin ground section is observed under transmitted light, the growthlayers are seen as the alternation of optical density. The decalcification and staining of a thin ground section partially masked with wax indicates that the opaquelayer in the cementum and dentine corresponds to the stainable layer (Pl. IV, Fig.
2). The minute layer in dentine is detected more clearly on decalcified and stained
slides.
The fetal dentine has a thick, uniform, moderately stainable layer, and theneonatal line is an unstainable layer of about 5 µm width deposited on the innerwall of fetal dentine. Three kinds of layers and presumably cycles are found in
the postnatal dentine. The first is the coarse layer and is the most conspicuous.
As discussed later, we believe that this layer represents the annual cycle. One
cycle of this layer is composed of a thin (about 10 to 20 µm in the first layer) conspicuous unstainable layer and a wide stainable layer. The unstainable layer isclearer near the cusp than at the root. The stainability in the stainable zone is
not uniform, but consists of finer layers ranging from 10 to 17 in number with amode at 12 or 13. This is the second kind oflayer, which may correspond to theshort cycle cemental layers in the teeth of the Baird's beaked whale, Berardius
bairdii, suspected by Kasuya (1977) to represent a lunar cycle or an endogenous
rhythm of about one month. Some of these fine layers deposited just prior to theunstainable layer of the annual cycle are always stained more strongly than thepreceeding stainable dentine which forms the stainable layer of the annual cycle.
In other words, the annual cycle of dentine deposition is formed by the enhanceSci. Rep. Whales Res. Inst.,
No. 31, 1979

49

FRANCISCANA DOLPHIN

ment of some of the shorter cycle layers. This cycle is inconspicuous in the thirdand successive annual layers. There are often observed several narrow layers(third layer) in some of the second kind of layers, but it is almost impossible tocount them.
In the cementum, the alternation of narrow stainable layers and wide weakly
stainable layers is the only way to read layers. From comparison with the dentinal
layers, it appears that the stainable cementum corresponds to the strongly stainabledentine deposited just prior to the unstainable layer of the annual cycle. This
cemental cycle is clearest usually on the cusp side of the cingulum.

1.2

Male

E
E

c

0

1.0

c

0

I
I

0

0.8

E

u 0.6

.....
0
I/)

0.4

Cll

~
u 0.2
.s::.

I-

,tQ

0

o,

•'

~

,'

,,--o
0

0

.

/Oat _a,oO<flro

0

0

.

0

0
0

00

tJ'

0

0

0

0 0
0
.,

0

•

cJJ

..

~~

o,,~

o

~/ 0
,'° •

0

I

ee
0

o•o
•

•

••

•

•

0
0

O/' 0

q, _,' 0

I'•,/

/'•

,
0/

I
I

O

•

0
0

~----'i- 0

,

0

I

0

O

Cll

0

8

I

I
I
I

0

0

oO
0

0 /•O

Cll

Ill

0

0

E
:J

Female

0

•
••

•It •

.· ...•.· . ..•.. .

~/I • tP/•·
~ f> .o : ...

1••

Body length in cm
Fig. 2. Scatter plots of thickness of cementum at cingulum on body length. Opencircle and dotted line indicate anterio-posterior thickness, and closed circle andsolid line ligual-buccal thickness.

Thickness of cementa[ layers
Figure 2 shows the maximum thickness of cementum at the cingulum plottedagainst the body length. The cementum was present on all the individuals, which
had at least some teeth erupted. There were three juveniles, one female (98.5 cm)
and two males (84.5 and 96.0 cm), where 20 to 30 teeth on each jaw were left
unerupted. The teeth of these individuals had cementum of 5 to 12 µm in thickness. Their postnatal dentine ranged from 65 to 110 µm in thickness, or 14 to
24% of the mean thickness of the first postnatal dentine shown in Table 3. These
data indicate that tooth eruption and cemental deposition starts as early as one
or two months after birth.
These is a great deal of individual variation in cementum thickness. This
would, in some degree, have been caused by technical problem with preparation.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

50

KASUYA AND BROWNELL

However, it is clear that the cementum is thicker on the anterio-posterior direction,and that there is no sexual dimorphism of the thickness if compared between individuals of the same body length.
The relationship between the thickness of cementum and age is shown in
Fig. 3. The deposition is faster in the first 3 years, and then changes to a slower
growth phase which seems to continue until at least 9 years of age. The difference
between sexes is not significant.
1.2

, .0

1
0

0.8
0.6

Cementum13i 1.:~~.:3~1
3 h.. 2

E

E 0.8
c 0.6

25r.6---<(-' /':c 0.4 /I/i
3

<I>

:

i

122

1 ·-o-----~13'

J.{ i 7 '5DentineI

E 0.2 ~l<I>~~ 1.60f:,~ 1.4 ~.

Pulp cavity"

1.2 '\
1.0

\25

0.8

\!2j1 1r .

0.4

l~17
! ',,:
! ',

0.2

'

0.6

5

i ·. 9! ''>-----6.. --- 1 --~ _ 11 _Ji... 3
2

2

5

4

6

8

.

1

10

12 13-

Age in years
Fig. 3. Relationship between anterio-posterior dimensions of the tooth and age.
Closed circle and solid line indicate mean value in males, open circle and dottedline that in females, vertical line observed range, and numerals the number ofsamples. For further explanations see text.

Thickness of dentinal layers
Figure 4 shows the relationship between body leng1~1. and thickness of dentine
measured at the level corresponding to the proximal end of the prenatal dentine.
There was no sexual dimorphism in the thickness nor any difference related to thedirection of the preparation. Although the dentine deposition is slow in juveniles
under 100 cm in body length, there is a sudden increase in the thickness at lengths
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

51

FRANCISCANA DOLPHIN

E
E

Femal<?

Male

c

e

0.8

c
....c 0.6e'O... 11:1 .. 9 ..

0

,

~

0

•oo

o

/

,'

.o.......... ~,.. 0

Cl.I

-

0;' 0

0

~

G>

0

•O

00 0

8.

U"~:

0.4

• o ,•O •

,,. •

0

•
0

.. 0 • • 0

Ill
Ill
G>

0•

00

~

•

o

•

·~

•

c 0.2

. •••

~

u

.c

!-

0

0

100

80

120

•

0

100

140

120

140

160

Body length in cm
Fig. 4.

Scatter plots of the thickness of dentine on body length.

For key see Fig.

2.
TABLE 3.

THICKl"iESS OF DENTINAL LAYERS OF PONTOPORIA BLAINVILLEI (in µm)
Lingual-buccal

Male
lst
2nd
3rd
Femalelst
2nd
3rd

An teri o-pos terior

No.

Mean

SD

No.

Mean

SD

53
28
4

432
206
133

88.3
55.7
10.4

:36
18
4

458
204
100

95.ti
57.4
24.5

56
27
4

462
214
95

81.3
66.4
32.4

55
34
14

469
202
102

88.8
71.8
40.6

of 100 cm in males and 105 cm in females, which is again followed by a slower increase.
The body length of rapid dentine deposition coincides with an age of 0.5 to 1.0 years(Fig. 7). The increase of dentine thickness is almost negligible after the age of
4 years, and this is reflected by the change of the diameter of pulp cavity (Fig. 3 ).
The diameter of the pulp cavity attains the minimum of 40 to 100 µm at about 4
years of age. This stage nearly coincides, as mentioned below, with the age when
the number of cemental layers exceeds that of dentinal layers of the same individual.
Furthermore, in these individuals, the pulp wall is covered by strongly stainablestructureless thin dentine. We consider that this is an indication of the cessationof dentine deposition or of the deposition of such a thin dentine that the growthlayers in it cannot be counted by the present method.

Accumulation rate of the layer
Figure 5 shows the relationship between the number of layers of dentine andcementum in the same individual. When there are less than four dentine layers,
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

52

KASUYA AND BROWNELL

the difference between these two figures is usually less than a fraction of a layer.
The number of dentine layers usually exceeds the number of cementa! layers bya small fraction because of the difficulty of distinguishing a thin incomplete layer
in the cementum. The two figures often disagree after the age of 4 layers in males
or 5 layers in females. This suggests that the accumulation rate of the layers in
the two tissues is the same up to an age of approximately 4 to 5 layers (=years).
After this age, it appears that only the cementa! layer retains the same deposition
rate. It must be noted, however, that age determination by means of cementa!
layers is less accurate than by dentinal layers.
Female

Male

0

•

. 2

z

0 0

B

10

No. of

2-Z.

5-9

•

10-

12

..

t

•

•

14

16

cementa!

2

10

4

12

layersFig. 5. Relationship between number of growth layers lil dentine and that in
cementum.
TABLE 4.
Month
Unstainable
Male
FemaleTotal, no.

",%

Stainable
Male
FemaleTotal, no.

",%

NATURE OF THE LAST INCOMPLETE DENTINAL LAYER
II

III

VI

0

0
.0
0
0.0

1
2
100.0

7
10
17
18.5

14.3

0
0
0
0.0

40
35
75
81.5

0
6
6
85.7

3
4
100.0

VIII

IX

x

XI

XII

2
66.7

0
0
0
0.0

0
2
2
100.0

0
2
2
40.0

10
2
12
27.3

0
2
2
100.U

0
0

0
3
3
60.0

13
19
32
71.1

0

33.3

0

0.0

The seasonal frequency of the condition of the last incomplete layer wasstudied only on the dentinal layers, because the observation is more difficult on
cementa! layers. Only individuals with less than three growth layers were used.
These results are shown in Table 4. There is some difficulty in determining thenature of the last incomplete layer, because of the presence of finer structures inthe dentine. This will increase the apparent individual variatiod in the seasonal
formation of a certain kind of layer. A sufficient number of samples was available only in December and January, when most of individuals (70 to 80%) were
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPHIN

53

forming the stainable type of dentine. The ratio seems to be higher in January
through June, but decreases from August to November when only half of 12 individuals are forming the stainable dentine. These data, together with the factthat the thickness of unstainable layer is less than 5% of the total thickness of one
dentinal layer, suggests that the period of the formation of unstainable dentine israther short in each individual and that it occurs at various times between Augustand November.
Figure 6 shows the seasonal change of the fractional part of the dentinal layercount. This is estimated by eye at the time of age determination without referringto the biological data or the date of death. The graph indicates that the thicknessof incomplete layer increases linearly from November to September of the nextyear, when the deposition ofunstainable layer seems to occur in most of individuals,
to complete one deposition cycle.
From the above analyses it is concluded that the coarse dentinal layer isdeposited annually. The cementa! layer deposition also follows the same cycle.
, '(

I j

/

,

80

/

,,

.£: 60

,,,,"

Ill
Ill

\

(!)

~ 40
u
.c

/

~:/

/

/

,,/ '•

I-

/

20

'/

//~
,.'//I'

0

/

N

D

I

J

A
F

•
M A M J
Month

J

A

S

0

Fig. 6. Seasonal change of the thickness of the last incomplete layers in dentine.
For explanations see text.

GROWTH

Length at birth
The largest fetuses encountered were a male and female 68 and 70 cm long,respectively. The three next largest fetuses were 66, 65, and 63 cm. The smallest
neonatal animals were two males 84 and 84.5 cm long. The two next smallest
dolphins were a male and female, both 85 cm in length. The next was a male
92 cm long. The age of the 84.5 cm neonate was estimated at 0.2 years. Therefore, we conclude that the body length at birth is greater than 70 cm and less thanSci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND BROWNELL

54

85 cm, probably in the low 70 cm range.
Postnatal growth in body length

The calves which are born at a length between 70 and 75 cm attain a mean
length of 96.2 cm (13 individuals, sexes combined) at the age of about 0.5 year.
Although the sexual dimorphism in the body length might be present at the age
below I year (Table 5 ), the observed difference is not significant (p= 0.2). The
growth is slower in males and the mean body lengths are significantly smaller thanthose of females after the age of 1 year (p<0.001). No secondary growth spurt isobserved in either sex. The present materials indicate that the growth ceases at
the age of 4 years (Fig. 7). The mean asymptotic length of 133.3 cm for males
and 153.0 cm for females are estimated as the mean body length of individuals
4 years or older.
If the Gompertz equation (Zweifel and Perrin, in press) is fitted for threemean lengths below 3 years by forcing to have the asymptotic length of 133.3 cm,
the least squares calculation gives following equation for males:
TABLE 5.
Age (yr.)

AGE AND BODY LENGTH (cm) IN PONTOPORIA BLAINVILLEI
Mean age

No.

Range

Mean

S.D.

0.3
1.2
2.2
3.3
l:i.2

5
48
21
2
21

84.0-102.0
90.5-134.0
110. 0-152. 0
118.0-129.0
122.0-147.0

92.7
115. 7
128.8
123.5
133.3

8.04
9.72
10.59

0.5
1.3
2.2
3.2
6.4

8
54
25
0
28

85.0-105.0
100.0-143.0
120.0-169.0
145.0-160.0
137.0-171.0

98.4
122.6
141.2
152.2
152.8

6.02
10.64
14.41
5.46
9.23

Male

o;;;;, <l1;;;;, <22;;;;, <33;;;;, <44;;;;, ;;;;16
Femaleo;;;;, <1l;;;;, <22;;;;, <33;;;;, <44;;;;, ;;;;13
TABLE 6.
Age (yr.)

8.58

AGE AND BODY WEIGHT (kg) IN PONTOPORIA BLAINVILLEI
Mean age

No.

Range

Mean

S.D.

0.3
1.2
2.2
3.0
8.5

4
21
10

10.9-17.2
11.8-24.5
16.3-35. 7
17.2
19.9-32.2

14.2
18.6
24.0
17.2
28.2

2.74
4.35
6.40

0.3
1.2
2.3
3.0
5.6

3
26
9

11.8-14.9
14.5-30.8
17.7-34.9
34.4
29.9-52.1

13 .1
22.9
26.3
34.4
40.3

1.59
4. 72
l:i. 76

Maleo;;;;, <I
1;;;;, <22;;;;, <33;;;;, <45;;;;, :;:;;; 16
Female1>o;;;;, <11;;;;, <22;;;;, <33;;;;, <44;;;;, ;;;;8
1> No

4

5

5.66

8.55

pregnant female included.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPHIN

55

170

E i:Jour·
7 ~L-.!-.-f---'--!--'---!~'---'---'--~1~0-'-~12,.......,--:1~1-'---!~'--7--'-~--'--7.--'--:~'--~10--!'--:1~2-'

Age in years
Fig. 7. Scatter plots of body length vs. age, males at the left and females at theright. Immature individuals are indicated by the larger closed circles, matureindividuals by open circles, and those of unknown maturity by the smaller closed
circles. Dotted line indicates an individual where number of cementa! layers(circle at the right end) is used instead of dentinal layers (left end of dotted line).
Growth curves are drawn by eye.

E 160
u

.£ 140..c
Oi 120
c:

~ 105

~100

:,?-~·

~
07.

o••

0

'°
Body weight in kg
Fig. 8. Scatter plots of body weight vs. body length (the x and y axes are reversedin this graph). Closed circles indicate males and open circle females. For
further explanations see text.

Yt = 133.3 exp( -0.5611 exp( - l.2447t))

where Yt indicates the body length (cm) at age t years. Although this equationfits well to the male data, the analogous equation for females does not fit the data.
This may be due to the fact that the growth of females is more specialized, that
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

56

KASUYA AND BROWNELL

is, females grow at a faster rate for a longer period.
Postnatal growth in body weightThe sexual dimorphism of body length suggests the presence of sexual dimorphism of body weight in all the age classes above I year of age. However, theobserved difference of mean body weight is significant only in the age group fromI to 2 years and that above 4 years (p<0.05). This is because of the large individual variation of body weight and small sample size.

•

January0• Julyo December

14

0

Cl

c: 12

0

Ill
C1I

iii 10

-Cl.I

..c.
0

8

.0
0

6

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

..c.

Cl

·~

~

.

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

4
Oo •

2

0
0

~
0

0

0

.

•

o.

•
o •o

0 ~~~~~~~-'-~~....I..-~--'~~-'-~--'
80
90
100
110
120
130
140
Body length in cm
Fig. 9. Scatter plots of combined weight of both testes on body length. Horizontal
lines indicate the mean weight at the attainment of puberty or of sexual maturity
calculated in this study.

In Fig. 8, the body weights are plotted against the body length. No sexual
dimorphism is observed in the relationship. This is reasonably expected from thefact that there is no observed secondary sexual dimorphism in the external proportions of the species (Kasuya, 1974). The correlation seems to change at a bodylength 105 cm. The relationship of the body weight to body length is expressedby the following equations calculated by least squares,y = 3.459x 10- 2 -x 1•2993 ,y = 6.902x I0- 5 ·x2 •6347 ,

x;;;;IOS
x~I05

where y indicates body weight in kg and x indicates body length in cm.

A bodySci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPHIN

57

length of 105 cm corresponds, on the mean growth curve, to an age between 0.5
and 1.0 year, or probable weaning period as discussed below. If the growth of
the body in the longitudinal and transverse directions is the same, the coefficientmust be close to 3.0. However, it is much smaUer in this species. This indicatesthat the body of the species becomes slender with the increase of body length andthe tendency is more exaggerated during the suckling stage.

Weaning
The stomach contents of only four juveniles were studied. The smallest,male, 84.5 cm, 0.2 years of age, had milk in the stomach. Also present were numerous small unidentified discs of a diameter of about 0.3 mm. Although the originof these substances is unknown, they may have been derived from some solid
food. More than half of the teeth had erupted in this individual. Three otherjuveniles, 90.5 cm to 104.5 cm in body length and 0.3 to 1.1 years of age, had fish
otoliths, squid beaks or shrimps in their stomachs. The presence of milk was notnoted.

Ol

14

c

12

IJ)

QI
......

10....Cl>

-

8

0

6

.c.

4

QI

2

..
~

Ol

3=

••

•

IJ)

....

•

•
•

~

•

..
••

•

•
•

•

• •

•

,

.. ··'
••
0
•• •
•

0

2

I

4

6

8

16

Age in years
Fig. 10. Scatter plots of combined weight of both testes on age.
lines see Fig. 9.

For horizontal

These data suggest that the species starts to take solid food at about 3 months
after birth. The length of the suckling was not determind. The rapid increase of
the dentine thickness at a length of 100 to 105 cm, which corresponds to an ageof 0.5 to 1.0 year, possibly coincide with the period when the diet changes frommilk to solid food as suggested in Stenella attenuata by Kasuya, Miyazaki and Dawbin(1974).

Attainment of sexual maturity in male
Figure 9 shows the relationship between body length and combined weight
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

58

KASUYA AND BROWNELL

of both testes. The weight is below 2 g in juveniles, but shows a rapid increaseat a length of 120 to 130 cm, which will correspond with the approach of sexual
maturity. The present data on the testes weight are limited mainly to the monthsof January, July and December. The seasonal change of the testes weight was
examined between these three months. Since the mating peak of the species is
estimated to be in December to February (Harrison et al., Ms.) there is expecteda difference of the weight between the winter and summer months. However,as shown in Fig. 9, there is no observed seasonal change in the present materials.
This is probably because the sample contains so few adult animals. In case of
Stenella coeruleoalba, the seasonal change of testes weight is observed clearly only inadults (Miyazaki, 1977).
Figure 10 shows the relationship between age and weight of testes based on
13 males in December, 25 in January and one in February. The increase of theweight is rapid between 2 and 2.5 years of age.
TABLE 7.
Weight 1>
(g)
0-2
2-4
4-6
6-8
8-10
10-12
12-14
1l

SEXUAL MATURITY AND WEIGHT OF TESTES IN PONTOPORIA BLAINVILLEI
Immature

MaturePuberty

no.

%

no.

~~

no.

%

9
7
4

100.0
87.5
50.0
16.7
0.0
0.0
0.0

0
1
0
2
2
0
0

0.0
12.5
0.0

0
0
4
3
5
0
2

0.0
0.0
50.0
50.0
71.4

0
0
0

33.3
28.6
0.0
0.0

100.0

Total
no.
9
8
8
6
7
0
2

Lower limit included.

The determination of sexual maturity in males is less accurate than that infemales. In the present study it was done based on the histological examinationof testis. The epididymal development was used only for a reference. By examining all the available seminiferous tubules in a slide which is usually a crosssection of the entire testis, an individual was classified as mature if all tubules contained spermatids or spermatocytes, as immature if no tubules contained them, andas pubertal if some of the tubules contained them. The spermatid and spermatocyte are always observed together and often accompanied by spermatozoa,
but the presence of only spermatozoon was not observed. This criterion is similar
to that used for Phocoenoides by Kasuya (1978), and is not based on direct data if
the individual participate in the reproduction.
The development of the ductus epididymis seems to be completed before thatof the testis. This is indicated by the facts that the pubertal testis is usually accompanied by an epididymis with a fully developed ductus, and some immature testis
by an epididymis with a partially developed ductus.
The relationship between the combined weight of both testes and the maturity
is shown in Table 7. The largest immature testes appeared at the weight of 7.6 g
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPHIN

59

and the smallest mature at 4.6 g. Pubertal stage testes at a weighed between 3.1
and 8. 7 g. The least squares regression gives 5.1 g as the weight where thefrequency of" immature" individuals is 50%, and 6. 7 gas that where half of theindividuals are " mature ". The former value corresponds to the mean weight of
the testes when males reach the pubertal stage (see Fig. 9). In the following analyses of the growth of the male, the identification of maturity is based on the resultof the histological examination of the testis. Weight criteria were not used because
they did not improve the accuracy of the analyses.
TABLE 8.

AGE AND MATURITY IN PONTOPORIA BLAINVILLEI
FemaleAge(range)Male-·------- - - ----·---

--~-

1~,

<2
2~, <33~, <44~, <55~, <6Age(mean)

Im
no.

Pu
no.

M

M

no.

%

1.2
2.2
3.2
4.1
5.0

48
10
0

0
3
0
0
0

0
5
5
10
4

0.0
27.8
100.0
90.9
100.0

0

-·---

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

Age(mean)

Im
no.

1.2
2.1

12
4
0
0
0

4.0
5.0

Pu
no.

0
1
0

---·--

M
no.

M

0
3
0

0.0
37.5

2

%

50.0
100.0

Im: Immature, Pu: Pubertal, M: Mature.
TABLE 9.

BODY LENGTH AND MATURITY IN PONTOPORIA BLAINVILLEI
Male

FemaleBody length(cm)
115-119120-124125-129130-134
135-139140-144
145-149- --------------------- --

Im
no.

8
10
4
2
0

Pu
no.

0
0
2
0

M
no.

0
0
2
4
7

---··------------------

M
<}~

0.0
0.0
28.6
50.0
10\J. 0

Im
no.
2
5
2
4
I

0

Pu
no.

M
no.

M

0

0
4

0.0
44.4
25.0
50.0
60.0
87.5
50.Ll

1
3

5

6
7
2

%

Im: Immature, Pu : Pubertal, M: Mature.

Table 8 shows the relationship bet\veen age and maturity. The age of theoldest immature male is 2.1 years, and that of the youngest adult male 2.0 years.
The pubertals male appeared between the age of 1.2 and 4.0 years. These data,
gether with the principal uncertainty of the definition of sexual maturity of the male,
allow us to say with certainty only that the mean age of the male at the attainmentof sexual maturity is between 2 and 4 years. However, the scatter plot of testes
weight againt age shown in Fig. 10 strongly suggests that the males attain maturity
at an age between 2 and 3 years as in the case of the females.
Table 9 shows the relationship between body length and the growth stage.
If the unusually large immature male (RLB 835, 145 cm, 35. 7 kg, and 2.0 yearsof age) is excluded, body lengths of the smallest mature male and of the largest
immature are 121 cm and 137 cm, respectively. The pubertal males are foundSci. Rep. Whales Res. Inst.,
No. 31, 1979

KASUYA AND BROWNELL

60

between 118 cm and 145 cm. The least squares regression fitted for the data
in Table 9 gives 124.8 cm as the length where half of the individuals are immature.
The corresponding figure calculated for the ratio of mature males is 131.4 cm.
The former corresponds to the mean length at the onset of the pubertal stage definedin this study and the latter to that at the onset of the mature stage. Possibly
the mean length at the start of actual adult stage lies between the two values.
If the large immature male (RLB 835) is excluded, the weight of the heaviest
immature male is 24.5 kg and that of the lightest mature males 29.0 kg. One
pubertal male weighed 24.9 kg (Table 10). Accordingly, the weight of male atthe onset of sexual maturity is estimated to be between 25 and 29 kg.
TABLE 10.
Body weight(kg)

21.0-23.9
24.0-26.9
27.0-29.9
30.0-32.9
33.0-35.9
36.0-38.9
39.0;;;;;

BODY WEIGHT AND MATURITY IN PONTOPORIA BLAINVILLEI
FemaleMale--------- - - - - - - - - - - - - - - - - -----------------

Im

Pu

M

Im

Pu

M

3
2
0

0

0
0
2
2
0

5
6
6

0

0
0

0
l

0
0

0
0
0
0
0

0

l

l

0
0
0

0
0

l

0
0

0
2
2
2

Attainment ef sexual maturity in female
The sexual maturity of the female was determined by the presence of at least
one corpus luteum or albicans in the ovaries. Some immature females with developed Graafian follicles were considered as being at the pubertal stage. The
youngest mature female appeared at the age of 2.0 years and the oldest immature
at 4.0 years. The pubertal females ranged in an age between 2.1 and 2.8 years.
The mean age at the attainment of sexual maturity is calculated from the ratio ofadult females in each age group shown in Table 8. The least squares equation isexpressed as follows:y = 28.52x-26.39,

1 ~x~6

where x indicates the age in years and y the ratio of adult females in percentage.
The age where half of the females are sexually mature, or the mean age at theattainment of sexual maturity, is 2. 7 years.
The smallest mature and the largest immature female were 137 cm and 146
cm in length, respectively. The pubertal females were found between 136 cm and144 cm in body length. The least squares regression of the data in Table 9 gives
140.3 cm as the body length where half of the females are sexually mature. Thisvalue is significantly smaller than the approximate length of 14 7 cm read on themean growth curve corresponding to the mean age at the attainment of sexual
maturity. This difference is caused by the cessation of growth in body length soonafter the onset of sexual maturity.
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPHIN

61

The body weight of the largest non-pubertal immature female was 30.8 kg(1.2 years of age), and pubertal females were found in the range between 29.0 kg(2 .4 years) and 33 .1 kg (2 .1 years). The smallest adult appeared at the bodyweight of 29.9 kg (4.0 years). All the females were sexually mature above theweight of 34 kg. Accordingly, it is expected that the female attains maturity at abody weight of 33 to 34 kg. The weight calculated for the mean body length at
the age at sexual maturity of 2. 7 years is about 35 kg, which is close to the above
figure.

Attainment of physical maturify
The fusion of vertebral epiphyses to the centrum was examined on a limited
number of individuals. The sexually immature individuals were, even if theepiphysis was not examined, reasonably considered in this study as physicallyimmature.
In the present sample only one male was physically mature. It was 132 cm
in body length and 16 years of age. The age of the oldest physically immature
males was 5 years, represented by two sexually mature males. Their body lengths
were 140 and 142 cm, respectively. Because of the scarcity of materials, it was
impossible to determine the difference of the age at physical maturity of males andthe corresponding value of females below.
The age of the oldest physically immature females was 4.0 years, and the age
range of five physically mature females was from 4.0 to 8.0 years. This indicates that females attain physical maturity at the age of about 4 years or about
1 year after the attainment of sexual maturity. The mean length of the femaleat the attainment of physical maturity will be very close to the asymptotic lengthof 153.0 cm estimated in the former section. The largest physically immature
female was 145 cm in body length, and the length of physically mature females
ranged from 148 to 171 cm.
DISCUSSION

Scott (1949) found in cetaceans the following linear relationship between the
maximum length of the adult, x in cm, and the neonatal length, y in cm:
y = 0.244lx+44.3(1)

Later, Ohsumi (1966) obtained for several species of odontocetes the following
allometric relationship between the mean length of female at the attainment ofsexual maturity, x in m, and neonatal length, y in m:
y = 0.532x 0•916(2)

If the asymptotic length of females 153.0 cm, and the mean length at the attainmentof sexual maturity, 147 cm, estimated in this study for P. blainvillei are put in theseequations, neonatal lengths of 81.6 cm and 72.6 cm are obtained from equations(1) and (2), respectively. The extraporation of the growth equation (page 55)
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

62

KASUYA AND BROWNELL

gives a neonatal length of 76.1 cm. These, figures, especially the second, are close
to the value estimaetd in the former section of this study.
The fetal growth rate al}d length of gestation can be deduced by the methodof Kasuya (1977) or of Perrin et al. (1977). When x indicates the neonatal lengthin cm and y the fetal growth rate in cm/day at the linear part of the growth curve,
the following equation was obtained from eight species of odontocetes (Kasuya,1977).
y = 0.001802x+0.1234

Accordingly, the length of time from the date when the extended straight feta!
growth line cuts the axis of time to the mean date of birth is calculated by x/(0.001802x+0.1234). If the neonatal lengths 81.6 cm and 72.6 cm are put inthe equation, the duration is calculated as 291 and 275 days, respectively. The
estimation of length of time from the start of gestation to the date when the extended linear growth line cuts the axis of time has some uncertainty. Hugget
and Widdas (1951) estimated for the growth curve indicated by the cube root of
the fetal weight that the length of time is 0.2 X (gestation time) for the gestation
over 400 days. Laws (1959) indicated that the value will be 90% of the value
estimated by Huggett and Widdas (1951), if the growth curve is based on thelength. After repeated calculations beginning with a gestation of 350 days (fordetails see Perrin, Coe and Zweifel, 1976), the values obtained for species P. blainvillei were 0.130 (for linear growth period of 291 days) or 0.139 (275 days). Thesefigures give a total gestation time of 334 days or 11.0 months (neonatal length of
81.6 cm) and 319 days or 10.5 months (neonatal length of 72.6 cm).
Perrin et al. (1977) found the following relationship between length of gestationin months (Y) and length at birth in cm (X).
LogY = 0.4586 LogX+0.1659

This equation and the neonatal lengths of 81.6 cm and 72.6 cm calculated above
give gestation lengths of 11.0 and 10.5 months respectively. Presumably the latter
figure, 10.5 months, will be closer to the true value. These estimates show a good
agreement with the range of 10.5 to 12 months obtained by Harrison et al. (Ms.).
Further improvement of the estimate will depend on a better calculation of theneonatal length.
The age at the attainment of sexual maturity, 2. 7 years, obtained for female
P. blainvillei is the lowest in any cetacean which has been studied. This may berelated to the small body size of the species. The only comparable species is Phocoena
phocoena, which in the western North Atlantic attains sexual maturity at the ageof 4 years (Gaskin and Blair, 1977). The same species in the North Sea is considered to attain maturity at 5 years in males and 6 years in females (Utrecht,1978).
The age frequency of the present materials is shown in Fig. 11, where only
the data of random collection are listed. A mode exists between 1 and 2 years.
The frequency of the calves below 1 year of age is only 13 individuals, and theSci. Rep. Whales Res. Inst.,
No. 31, 1979

63

FRANCISCANA DOLPHIN

!!20
<U
:J

u

.~10
-0

c

7
/

..... 5

\\

0

ci 3

\

z

2
1
0

/\\

2

4

\

/
b.- --o'68er- --016

1012

Age in years
Fig. 11. Age frequency of P. blainvillei. Closed circle and solid line indicate males,
and open circle and dotted line females. Only the random catch samples areincluded.

presence of bias in the sample is suggested. According to Harrison et al. (Ms.)
the parturition peak of the species is in the second half of November to the second
half of December (depending on the estimation of the mean neonatal length).
Since most of the present materials were obtained in December and January,
there should have been more newborn calves if the materials were not biased.
The number of pregnant females, namely the number of calves which would
have been born in the next year, is close to the number of calves below 1 yearof age. This is again an indication of the under representation of pregnant
females, and presumably that of other adult individuals of both sexes. This bias
may cause an error in the estimation of the mean age at the attainment of sexual
maturity, the mean growth curve after this age, and the maximum length of lifespan. However, since the correlation between age and sexual maturity is very
high in the present species, the bias in the estimation of the first two figures will
be slight. Samples bias related to the method of fishing is known in Stenella
coeruleoalba and Phocoenoides dalli (Kasuya, 1978).
Though catchability might be different between the sexes, the difference wasnegligible in the immature individuals. The ratio of females in the total of 148
individuals below 3 years of age is 50.0%. This is considered to be close to thereal sex ratio at the immature stage.
Among 27 adult females dealt with here, the reproductive stage is known in
15 individuals. They are seven pregnant, two pregnant and simultaneously
lactating, three lactating, and three resting females. The last category indicates
adult females neither pregnant nor lactating. The lactating or resting females arelimited to December and January, the parturition season of the species. The
Sci. Rep. Whales Res. Inst.,
No. 31, 1979

64

KASUYA AND BROWNELL

data from other months are one pregnant in August, two in October, and two
in November. These data suggest that lactation usually lasts a short period, presumably not longer than eight or nine months. This figure is in good agreementwith the length of nursing:period estimated in the former section. Females which
weaned a calf before August or September will become pregnant in the next mating season in January. Accordingly we suspect that a two years cycle of breeding will be most frequent in this species.
ACKNOWLEDGMENTS

This study would not have been possible without the cooperation and assistanceof all the fishermen of Punta del Diablo and especially the Olivera family who
made our work in the village possible. Major financial support came from the
National Geographic Society, Office of Naval Research, National Science Foundation (grant number GF-42389), Ministry of Education, and Japanese Society for the
Promotion of Science. The following individuals helped in various ways during thisstudy: M.A. Klappenback, J. G. Mead, A. Mones, M. Nishiwaki, R. Praderi, S.
Toscano, and A. Ximenez. T. Kamiya, K. Numachi, and F. Yamasaki helped
us collect specimens in Punta del Diablo. M. Oya and S. Wada assisted withmany phases of the data handling and processing. We thank all these persons
for their help.
REFERENCESBROWNELL, R. L. JR. and R. NESS, 1970. Preliminary notes on the biology of the Franciscana, Pontoporia
blainvillei (Cetacea, Platanistidae). pp. 23-28. Jn: Proc. Sixth Annu. Conf. Biol. Sonar and Diving
Mammals, Stanford Res. Inst., Menlo Park, Calif.
BROWNELL, R. L. JR., 1975. Progress report on the biology of the Franciscana dolphin, Pontoporia blainvillei,
in Uruguayan waters. J. Fish. Res. Bd. Canada, 32 (7): 1073-1078.
GASKIN, D. E. and B. A. BLAIR, 1977. Age determination of harbour porpoise. Phocoena phocoena (L), in
the western North Atlantic. Can. J. Zoo!., 55: 18-30.
HARRISON, R.J., M. M. BRYDEN, D. A. McBREARTY, and R. L. BROWNELL, JR., (Ms). The ovaries and reproduction in Pontoporia blainvillei (Cetacea, Platanistidae).
HuGGET, A. ST. G. and W. F. WmnAS, 1951. The relationship between. mammalian foetal weight andconception age. J. Plrysiol. 114: 306-31 7.
KASUYA, T., 1973. Freshwater dolphins and their biology. Dobutsu to Shizen (Tokyo), 3 (12): 4--8. (InJapanese)
KASUYA, T., 1974. Morphology and growth of Franciscana dolphin pp. 12-24. In: Report of Scientific
Expedition of La Plata and Amazonian Dolphins, Univ. Tokyo Freshwater Dolphin Expedition, Tokyo
93 pp. (In Japanese)
KASUYA, T., 1977. Age determination and growth of the Baird's beaked whale with a comment on the feta!
growth rate. Sci. Rep Whales Res. Inst., 29: 1-20.
KASUYA, T., 1978. The life history of Dall's porpoise with special reference to the stock off the Pacific coastof Japan. Sci. Rep. Whales Res. Inst., 30: 1-63.
KASUYA, T., N. MIYAZAKI, and W. H. DAWBIN, 1974. Growth and reproduction of Stenella attenuata in the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst., 26: 157-226.
LAws, R. M., 1959. The foetal growth rates of whales with special reference to the fin whale, Balaenoptera
physalus Linn. Discovery Rep., 29: 281-307.

Sci. Rep. Whales Res. Inst.,
No. 31, 1979

FRANCISCANA DOLPH!.:\"

65

MIYAZAKI, N., 1977. Growth and reproduction of Stenella coeruleoalba off the Pacific coast of Japan. Sci.
Rep. Whales Res. Inst., 29: 21-48.
0HsUMI, S., 1966. Allomorphosis between body length at sexual maturity and body length at birth in the
Cetacea. ]. Mamm. Soc. Japan, 3 (1): 3-7.
PERRIN, W. F., J.M. CoE, and J. R. Zweifel, 1976. Growth and reproduction of the spotted porpoise,
Stenella attenuata, in the offshore eastern tropical Pacific. Fish. Bull. 74 (2): 229-269.
PERRIN, W. F., D. B. Holts, and R. B. Miller, 1977. Growth and reproduction of the eastern spinner dolphin,a geographical form of Stenella longirostris in the eastern tropical Pacific. Fish. Bull. 75 (4): 725-750.
PILLER!, G., 1971. On the La Plata dolphin Pontoporia blainvillei off the Uruguayan coasts. Investigations on
Cetacea (Berne), 3 (1): 59-68.
SCOTT, E.O.G., 1949. Neonatal length as a linear function of adult length. Pap. & Proc. Roy. Soc. Tasmania,
1948: 75-93.
UTRECHT, W. L. VAN., 1978. Age and growth in Phocoena phocoena Linnaeus, 1758 (Cetacea, Odontoceti)
from the North Sea. Bijdragen Tot de Dierkunde., 48 (1): 16-28.
VAN ERP, I., 1969. In quest of the La Plata dolphin. Pac. Discovery, 22 (2): 18-24.
XIMENEZ, A., A. LANGGUTH, and R. PRADER!, 1972. Lista sistematica de los mamiferos de! Uruguay.
Anal. Mus. Nacional Hist. Nat. Montevideo, Ser. 2, Vol. 7: 1-49.
ZWEIFEL, J. R. and W. F. PERRIN, in press. Fitting curves to odontoceti length tooth layer data. In:
Proc. Int. Conf. Age Determ. Odont. Cetaceans and Sirenians. Rep. Int. Whal. Comm. Spee. Issue.

Sci. Rep. Whales Res. Inst.,
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66

KASUYA AND BROWNELL

EXPLANATION OF PLATESPLATE I
Fig. I. Immature testis. RLB809, body length 111 cm, weight of testes I. 7 g, age
2.0 years. 19 Dec. 1972. Scale indicates 0.1 mm.
Fig. 2. Pubertal testis. RLB821, body length 130 cm, weight of testes 3.1 g, age
2.2 years. 24 Dec. 1972. Same magnification with Fig. I.
Fig. 3. Mature testis. AOl972-4, body length 124 cm, weight of testes 5.8 g.
29 July 1972. Same magnification with Fig. I.
Fig. 4. Mature epididymis. A01972-4. Same magnification with Fig. I.
PLATE II
Decalified and stained thin _sections of teeth. Scale indicates 2 mm, all figures insame magnification. C, cementum. Open circle, neonatal line in dentine.
Fig. I. RLB600, 0.2 dentinal layers, 84 cm male, 14 Jan. 1971. Immature.
Fig. 2. RLB861, 0.4 dentinal layers, 103 cm female, 4 Jan. 1973. Immature.
Fig. 3. RLB648, 1.5 dentinal layers and 1.8 cementa! layers, 105 cm female, 27Jan. 1971. Immature.
Fig. 4. RLB698, 2.5 dentinal layers and 2.3 cementa! layers, 120 cm male, 18
March 1971.
PLATE III
Decalcified and stained thin sections of teeth. Scale indicates 2 mm, all the figuresin same magnification. C, cementum. Open circle, neonatal line in dentine.
Fig. I. A01971-54, 4.0 dentinal layers and 4.5 cementa! layers, 157 cm female,
24 Dec. 1971.
Fig. 2. A01971-57, 6 dentinal layers and 8 cementa! layers, 153 cm female, 30
Dec. 1971. Sexually mature.
Fig. 3. RLB592, 7 dentinal layers and 13 cementa! layers, 144 cm female, 14 Jan.
1971. Sexually mature.
PLATE IV
Fig. I. Decalcified and stained thin section of a tooth. RLB577, 6 dentinal layers
and 7 cementa! layers, 125 cm male, 5 Jan. 1971. Sexually mature. Scale indicates 2 mm. For other marks see Plate III.
Fig. 2. Decalcified and stained preparation of partially masked tooth. Left half,
undecalcified thin section; right half decalcified and stained part. RLB878,
133 cm male, 16 Jan. 1972. Immature. Scale indicates 1 mm. Photographed
under transmitted light. For marks see Fig. 1.
PLATE V
Comparison of annual layers in dentine and cementum Scale indicates 0.5 mm, allfigures in same magnification. Bar, boundary of prenatal and postnatal dentine.
C, cementum. Closed circle, annual growth layers.
Fig. 1. RLB600. Same tooth with Plate II, Fig. I.
Fig. 2: RLB861. Same tooth with Plate II, Fig. 2.
Fig. 3. RLB648. Same tooth with Plate II, Fig. 3.
Fig. 4. RLB698. Same tooth with Plate II, Fig. 4.
PLATE VI
For explanations see Plate V.
Fig. I. A01971-54. Same tooth with Plate III, Fig. I.

Deposition of osteodenSci. Rep. Whales Res. Inst.,
No. 31, 1979

67

FRANCISCA.NA DOLPHIN
tine started.
Fig. 2. AOl971-57. Same tooth with Plate III, Fig. 2.
most of pulp cavity leaving narrow canals.

Osteodentine nearly fills

PLATE VIIFor explanations see Plate V.
Fig. I. RLB592. Same tooth with Plate III, Fig. 3. Deposition of osteodentine
started on some part of pulp wall.
Fig. 2. RLB577. Same tooth with Plate VI, Fig. I. Central part of pulp cavity
is almost filled by osteodentine.

Sci. Rep. Whales Res. Inst.
No. 31, 1971

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