THE RELATIONSHIP BETWEEN DEVELOPMENT OF THE
BONY FALX AND BONY TENTORIUM IN
CETACEANS AND THEIR DIETSTAKAO NOJIMA 1)
ABSTRACTThe correlation between food habits and ossification in the falx cerebri (FC)and tentorium cerebelli (TC) of cetaceans is considered.
I have observed the bony falx (BF) and bony tentorium (BT) in a variety
of mammals, including cetaceans, and have classified them into the carnivore
type and the dolphin type based on their developmental pattern. The carnivore type develops as part of the skull bones during the fetal period, andthese, attaining shapes closely similar to those of adults, are already completed at birth. The dolphin type, on the other hand, is formed by ossification in the FC and TC during the course of aging.
Among cetaceans, the dolphin type BF and BT are seen only in delphinids and phocoenids. The carnivore type BF and BT are present in all theZiphiidae, and in the sperm whale (Physeter catodon). In the other cetaceansobserved, neither the BF nor BT was seen at all.
I have reviewed many reports on food habits of cetaceans and noted thatthe cetaceans which possess the dolphin type BF and BT are fish-eaters(ichthyophagi). Many fishes contain a large amount of vitamin D which promotes ossification of bones, while squid and zooplankton, other main food of
toothed whales and the main food of baleen whales, respectively, contain novitamin D.
It appears likely that formation of the dolphin type BF and BT in delphinids and phocoenids is due to their continual intake of large amounts offish high in vitamin D.
Although this approach to assessing the food habits of cetaceans is indirect, it provides consistent results. The general trend of their food habits
throughout life appears to be reflected in the degree of ossification in the FC
and TC, much as the growth layers formed in teeth and ear plugs of cetaceans indicate their ages.
Key words: bony falx, bony tentorium, ossification, vitamin D1) 5-21-1,

Ooto, Yono-shi, Saitama, 338 Japan

Sci. Rep. Cetacean Res.,
No. 1, 1990, 39-61

40

NOJIMAINTRODUCTION

The brain of mammals is surrounded by three membranes, or meninges: thedura mater, the arachnoid mater and the pia mater. The dura mater is a dense,
strong fibrous membrane, and is conventionally described as two layers: theouter (endosteal) and inner (meningeal) layers. The outer layer is the periosteum
covering the inner surface of the skull bones. The inner layer is the dura materproper, and sends four partitions inward, which divide up the cranial cavity into
freely communicating spaces lodging the subdivisions of the brain. These partitions operate to restrict the rotatory displacement of the brain.
The falx cerebri (FC) is a vertical partition that lies in the longitudinal
fissure between the cerebral hemispheres. The tentorium cerebelli (TC) is apartition that inserts between the upper surface of the cerebellum and theoccipital lobes of the cerebral hemispheres, and forms a floor supporting thelatter (Plate I, Fig. 2). In most mammals, both the FC and TC are composed ofonly the folded dura mater. In other mammals, a bony plate, developed to varying degrees, is present in the FC and/or TC. The plate in the FC is the bony falx(BF) and that in the TC is the bony tentorium (BT).
There are few studies on the BF and BT of any mammals. I have examined
the skulls of 189 species in 54 families from 15 orders (but not Scandentia,
Dermoptera, Hyracoidea, Tubulidentata and Macroscelidea) in the class Mammalia (following Corbet and Hill, 1986).
The BT and/or BF were observed in almost all species of Carnivora and inmany species of Odontoceti (Cetacea), but were seen only in a few species
belonging to orders such as Perissodactyla (Equidae), Sirenia, Primates(Cebidae, genus Ateles) and Marsupialia.
Based on their developmental pattern, I have classified the BF and BT of
mammals into two types: the carnivore type and the dolphin type (Nojima,1988).
The BF and BT of the carnivore type develop as part of the skull bones(the parietal bone and/or occipital bone) during the fetal period, and these
attain shapes very similar to those of adults by the time of birth in almost all
carnivores (BT, and also the BF in all pinnipeds) and in horses (BT), phalangers(Phalangeridae) (BT), kangaroos (Macropopidae) (BT), sperm whales(Physeteridae) (BF), beaked and bottlenose whales (Ziphiidae) (BF & BT) andsirenians (BF). Morphological characteristics of the BT and BF are useful in theclassification of Carnivora (Nojima, 1990a).
On the other hand, the BF and BT of the dolphin type, for example thoseof spotted dolphins (Stenella attenuata), are not seen in the newborn or juvenileat all, but are gradually formed by ossification in the FC and TC as the animal
grows older (Nojima, 1988, 1989). Among cetaceans, clearly formed dolphin
type BF and BT are seen only in the Delphinidae and Phocoenidae. The BT of
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

41

spider monkeys is also assigned to this type (Nojima, 1990b).
The differences between the two types are not merely due to the differencein timing of onset of their development. In mammals which possess the carnivore type BT and/or BF, the membranous portions of the TC and FC in which
the BT and BF are absent, do not ossify throughout life (Nojima, 1990a). The
functional significance of the carnivore type BT and BF is unknown.
In previous studies (Nojima, 1988, 1989), I have suggested that ossificationin the FC and TC of delphinids and phocoenids may be due to the continual
intake of a large amount of fish high in vitamin D and calcium.
Vitamins D 2 ( ergocalciferol) and D 3 ( cholecalciferol) operate to maintaincalcium homeostasis in mammals after being converted to 25-hydroxyvitamin
D. Both are obtained from food. Vitamin D 3 is also obtained from exposure ofskin sterols to ultraviolet radiation. Deficiencies are more likely to become aproblem for housed animals which are not exposed to direct sunlight (Doyle,1987). Vitamin D deficiencies affect bone development (rickets) in young,growing animals and cause osteomalacia in adults (see for example Coburn,Hartenbower and Norman, 1974; Delucca, 1974; Fraser, 1975; Doyle, 1987).
On the other hand, hypercalcemia, which causes hyperplasia of bones andextensive calcium deposition in soft tissue, especially kidneys and arteries,
results from excessive use of the vitamin and calcium in the treatment of
humans for rickets (Kure and Sakamoto, 1966; Ishii, 1973; Coburn et al., 1974;
Delucca, 1974; Fraser, 1975; Nakayama, 1975; Kobayashi, 1989). According to
Schultze and Lubosch (1935), the dura mater of humans may be ossified,although it is unknown whether the condition is caused by hypercalcemia.
Most mammalian food in nature do not contain enough vitamin D to cause
toxicity. In fish-eating mammals such as certain pinnipeds and cetaceans, however, there is a danger that excessive intake of vitamin D could produce levels
known to be toxic for many terrestrial mammals (Bouillon, Vankerkhove and
De Moor, 1976; Keiver, Draper and Ronald, 1988a). Fish contain large
amounts of vitamin D, especially in the liver, and are the only source of thevitamin for cetaceans.
Food habits of cetaceans have been studied mainly by the examination of
stomach contents. However, with the exception of larger whales whose food
habits have been studied extensively using samples obtained from the commercial whaling industry, sufficient data for most toothed whales are not available.
Among cetaceans, clearly ossified BF and BT in the FC and TC, respectively, are seen only in the Delphinidae and Phocoenidae which have beenreported to ingest a large amount of fish. On the other hand, little or no ossification occurs in the FC and TC of other cetaceans reported to feed mainly onsquid, zooplankton or other invertebrates that lack vitamin D.

Sci. Rep. Cetacean Res.,
No. 1, 1990

NOJIMA

42

RESULTS

The dolphin type BF and BT were observed in all the Delphinidae andPhocoenidae, and are probably present in the Monodontidae. The carnivore
type BF and BT were observed in all the Ziphiidae. The carnivore type BF was
also observed in the sperm whale (Physeter catodon). In other cetaceans
studied, neither the BF nor BT was seen at all.
All cetacean species and the number of skulls studied, their main food, andthe BF and BT types are given in Table 1.

TABLE 1. LIST OF CETACEANS EXAMINED, TYPE OF BF AND BT, AND MAJOR FOOD ITEMS 1l.
Family and species(Sample number in parentheses)
Platanistidae
Pontoporia blainvillei (2)Inia geoffrensis (1)Platanista gangetica (3)Delphinidae
Steno bredanensis (4)Sousa teuszii (1)Stenella attenuata (35)
Stenella coeruleoalba (12)Stenella longirostris (3)Delphinus delphis (4)Tursiops truncatus (6)Lissodelphis borealis (2)Lagenorhynchus obliquidens (4)Lagenorhynchus albirostris (2)Lagenorhynchus obscurus (1)Lagenodelphis hosei (1)Peponocephala electra (5)Pseudorca crassidens (2)Orcinus area (2)Grampus griseus (3)Globicephala macrorhynchus (4)Feresa attenuata (4)Phocoenidae
Phocoena phocoena (6)Phocoenoides dalli (9)Neophocaena phocaenoides (2)Monodontidae
Monodon monoceros (1)Physeteridae
Physeter catodon (2)Kogia breviceps (2)Kogia simus (3)Carnivore
type

Dolphintype

Main foodcrustaceans, molluscs,
and fish (low vitamin
D content)

BF

BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF & BT (tiny)
BF&BT
BF&BT

fish & squid
fish & squid
fish
fish
fish
fish & squid
fish & squid
fish & squid
fish & squid
fish & squid
fish & squid
fish &squid
squid & fishsquid & fish
fish & squid
squid
squid & fishsquid & fish

BF&BT
BF&BT
BF & BT (tiny)

fish & squid
fish & squid
squid, shrimp, fish

BF & BT (tiny)squid & fish
squid
squid
squid

Sci. Rep. Cetacean Res.,
No. 1, 1990

43

BONY FALKS AND BONY TENTORIUM OF WHALES

Ziphiidae
Berardius bairdii (4)Ziphius cavirostris (7)Mesoplodon ginkgodens (2)Mesoplodon stejnegeri (2)Mesoplodon densirostris (1)Hyperoodon ampullatus (1)Balaenidae
Balaena glacialis (1)Eschrichtiidae
Eschrichtius robustus ( 1)Balaenopteridae
Balaenoptera borealis (l)Balaenoptera edeni (1)Balaenoptera acutorostrata (2)Megaptera novaeangliae (1)

BF&BT
BF&BT
BF&BT
BF&BT
BF&BT
BF&BT

squid
squid
squid
squid
squid
squid
zooplankton
amphipods
zooplankton
zooplankton
zooplankton
zooplankton

1) Classification of cetaceans is basded on Corbet and Hill (1986). The skulls of cetaceans belonging to thecollections of Department of Zoology, National Science Museum, Tokyo, were mainly studied. In many
species, both adult and juvenile specimens were studied for comparison of the degree of development of the
BF and BT. The growth stages (adult or juvenile) and other biological data in the text were copied frommuseum records. Besides these, a sperm whale of the Whale Museum, Ayukawa, Miyagi, a right whale of the
Whale House, Kumomi, Shizuoka. Twenty-seven spotted dolphins including fetuses, five striped dolphins,
and three bottlenose dolphins including a newborn are from my own collection.
Main food of each species is based on published reports. "fish & squid" or "squid & fish", respectively,means that the former appears to be more important than the latter.

Delphinidae
The BF and BT, which had been formed in varying degrees in the FC and TC,
were observed in most delphinids. In most of the juvenile animals observed,
the BF and BT had not been completed as a continuous bony plate (Plate II),but in some other juveniles, only a small bony process was seen to project fromthe portion corresponding to the internal occipital protuberance. The BF and
BT were not seen at all in fetal or juvenile spotted dolphins (Plate II), or in a
newborn bottlenose dolphin (Tursiops truncatus).
The Risso's dolphin (Grampus griseus) was a peculiar species. Even in
adult specimens, only a small ossified process projected from the portion corresponding to the internal occipital protuberance.
In the skulls of adult spotted dolphins, in which the BF and BT had been
completed (Plate I), the inner surface of the calvaria had been made rough bymany laminations formed by ossification in the dura mater (Plate III).
As an example of a delphinid pattern, the order of ossification in the FC
and TC of spotted dolphins is shown diagrammatically in Fig. 1.
Sci. Rep. Cetacean Res.,
No. 1, 1990

44

NOJIMA

Fig. 1. The order of ossification in the FC and TC of the spotted dolphin. The cranium
has been cut along a line slightly lateral and parallel to the midline and the right half has
been removed. The BT of the right side has also been cut along the same side of the
midline, and the BF and the inferior surface of the left BT are shown.
During 6 months to 1 year of age, ossification begins at the attachment of the FC
and TC to the internal occipital protuberance (1), and advances forward along the junction of the FC and TC. Then ossification spreads toward the back part of the FC andtoward the anterior portion of the TC (2). At the same time, ossification occurring in
the attachment of the TC to the base of the skull also advances upward in the anterior
portion of the TC (2), and fuses with the above developing plate to form the anterior
half of the BT. From this, ossification spreads backward in the TC (3). At the sametime, ossification in the FC advances forward and completes the free margin of the BF(3). Finally, by about 9-11 years of age, the BF and BT are completed in the shape ofthe entire FC and TC, except for the passage of blood vessels (black arrows) and nerves(V). The most anterior portion of the free margin of the TC is ossified to form a small
bony arch above the base of the skull (A). A shallow groove for the continuations of the
spinal meningeal artery to the ophthalmic retial complex runs under the arch (see Plate
I). The passage of the trigeminal nerve, which occurs at the most medial and inferior
portion of the TC, is completed as a foramen on the BT in older specimens (V), but
remains as a round notch at the free margin of the BT in younger specimens.

Phocoenidae
In both habor and Dall's porpoises (Phocoena phocoena and Phocoenoides
dalli), the BT had not been completed as a continuous bony plate to the base of
the skull in any specimens. The BF was well developed in older specimens, anda round opening for the passage of the trigeminal nerve, which in the spotted
dolphin is completed late during the process of ossification in the FC and TC(see Fig. 1), occurred at the partial BT projecting from the base of the skull.
The BF and BT of adult porpoises observed appear to have been damaged during preparation of the skulls. In all young specimens, both the BF and BT werepoorly developed.
Even in adult specimens of the finless porpoise (Neophocaena phocaenoides), only a small bony process projected from the portion which corresponded to the internal occipital protuberance.
Sci. Rep. Cetacean Res.,
No. l, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

45

Fig. 2. Schematic drawings of the BF, BT and TC of Ziphiidae; seen from left sideslightly anteriorly, and from below (right side).
BF: bony falx, BT: bony tentorium, TC: tentorium cerebelli, V: the passage of thetrigeminal nerve, which occurs as a foramen or a notch. Attachments of the TC of
Mesoplodon spp. are slightly ossified (black arrows).

Monodontidae
Only one specimen of adult male narwhal (Monodon monoceros) was
examined. The BF and BT were not seen in the skull; however, the portion
corresponding to the internal occipital protuberance was rough, probably
reflecting damage to the ossified process.
Physeteridae
Owen (1866) reported the partial BF projecting from the supraoccipital bone
into the back part of the FC in an advanced fetal sperm whale. I also observed
the partial BF in both young and adult sperm whales (12.19 m and 16.90 m inbody length) at the site corresponding to Owen's descriptions. The BT was
absent. The partial BF of sperm whales is assigned to the carnivore type.
Ziphiidae
The BF, which appears to have the shape of the entire FC, and the partial BT
which inserts into the posterior half of the TC, were seen in all the Ziphiidae,
including both young and juvenile specimens (Fig. 2, left side). In the mediansagittal section of an adult skull of Baird's beaked whale (Berardius bairdii), it
was obvious that the element of the BF and BT was derived from the occipitalbone (the supraoccipital bone). The BF and BT of Ziphiidae are assigned to thecarnivore type, and characterize the skull of those animals.
In all the Mesoplodon species observed, the attachments of the TC werepartially ossified (Fig. 2, right side), but not considered to be ossified in theentire shape of the TC.
Sci. Rep. Cetacean Res.,
No. 1, 1990

46

NOJIMADISCUSSION

Among prey items for wild mammals, some species of fish contain an exceptionally large amount of vitamin D concentrated in the liver. According to Kagawa(1989), vitamin D value in fish meat is fairly high on migratory fishes but is low
in most bottom-dwelling fishes and freshwater fishes. Holmes, Tripp andSatterfield (1941) and Inagaki (1970) reported vitamin D value (JU/gram) in fish
liver oil of some species (bluefin tuna Thunnus thynnuis, 27,000~70,000 IU;
skipjack Euthynnus pelamis, 20,000 IU; mackerel Scomber japonicus, 5,400 IU;
swordfish Tetrapturus audax, l,550~25,000 IU; halibut Hippoglossus hippoglossus, 550~20,000 IU). Although available data on vitamin D content in fish
liver oil are scarce, this can estimate from the vitamin value in the meat. Vitamin D content in the liver oil tends to increase in parallel with the increase of
the vitamin value in the meat. For example, the meat of dogfish Squalus
acanthias and blue shark Prionace glauca contain no vitamin D, and liver oilmade from these fishes only contain the vitamin of O~ 100 IU per gram. While
the meat of bluefin tuna and skipjack, above species respectrively, contains
about 600 IU and 420 IU per lOOg.
On the other hand, squid, zooplankton and the other aquatic invertebrates
contain no vitamin D (Hirano, 1982; Kagawa, 1989).
In the following sections, the correlation between degree of ossification in
the FC and TC and prey items of each group of cetaceans are discussed.

Mysticeti
Although the minke whale (Balaenoptera acutorostrata), sei whale (B.borealis),
Bryde's whale (B.edeni) and humpack whale (Megaptera novaeangliae) havebeen reported to ingest considerable amounts of fishes such as sardine, saury
and mackerel (Mizue, 1951; Nemoto, 1957, 1959; Mitchell, 1975), in many areas
the main food of these cetaceans is zooplankton such as euphausiids andcopepods (Nemoto, 1957, 1959, 1962; Nemoto and Nasu, 1958; Nemoto andYoo, 1970; Kawamura, 1970, 1973, 1977, 1980, 1982). The percentage of fish
found in the stomachs of minke and sei whales caught south of 40°S was 0% and
0.1 % , respectively (Horwood, 1987), and those of sei and Bryde's whalescaught in the North Pacific was 3.4% and 11.1%, respectively (Nemoto and
Kawamura, 1977).
The gray whale (Eschrichtius robustus) feeds primarily on benthic amphipods, especially gammaridean amphipods (Pike, 1962; Nerini, 1984; Wolman
1989).
North Pacific right whale (Balaena glacialis) feeds primarily on copepods
such as Ca/anus cristatus and C.plumchrus (Omura, 1958; Omura, Ohsumi,
Nemoto, Nasu and Kasuya, 1969).
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

47

No ossification in the FC and TC occurs in any baleen whales that are feeding mainly upon zooplankton with no vitamin D.

Physeteridae
Many reports on the food of sperm whales have been presented (Pike, 1950;
Mizue, 1951; Rice, 1963; Okutami and Nemoto, 1964; Roe, 1969; Kawakami,
1976; Clarke, 1980). Clarke (1956) examined a considerable number ofstomachs of sperm whales in the Azores, and found eight species of squid which
predominated in the stomachs and a small though not insignificant amount offish. Kawakami (1980) reviewed the published reports on the food of sperm
whales taken from different localities of the world. According to this, the percentage of squid and fish found in the stomachs obviously show that the sperm
whales are primarily squid-eaters although in some localities their stomachs
contained fairly high percentages of fish.
The pygmy sperm whale (Kogia breviceps) feeds mostly on cephalopods(Hale, 1947; Raun, Hoese and Moseley, 1970; Clarke, 1986; Pinedo, 1987).
Stomachs of the dwarf sperm whale (Kogia simus) contained large amounts ofcephalopods (Ross, 1978; Jones, 1981). Nagorsen and Stewart (1983) also foundcephalopod beaks and shrimp in the stomach. On the other hand, Fitch and
Brownell (1968) observed otoliths of many fish species (Ichthyococcus sp.,
Macrouridae, Moridae, Lampadena etc.) besides cephalopod beaks and crustacean remains in the stomachs of three pygmy sperm whales (?, scientific namegiven in the article is Kogia simus). However, only small amounts of fish appear
to be eaten by the species.
In the sperm whale, pygmy sperm whale and dwarf sperm whale, all ofwhich feed mainly on squid with no vitamin D, ossification in the FC and TC
does not occur at all, although the carnivore type BF is present in the sperm
whale.
Ziphiidae
According to reviews on the food of the Ziphiidae by Gaskin (1976), Evans(1987), Balcomb (1989), Heyning (1989) and Mead (1989a,b), the Ziphiidae on
the whole appear to be squid-eaters. Heyning (1989) listed many species of
cephalopods found in the stomachs of Cuvier's beaked whales (Ziphius cavirostris). Baird's beaked whale (Berardius bairdii) and Cuvier's beaked whale also
eat somewhat a considerable amount of deep-sea fishes (Rice, 1963; Nishiwaki
and Oguro, 1971). Almost all deep-sea fishes, however, are distinctly low invitamin D content.
Ross (1984) found 21 fish otoliths identified as species of the genera
Cepola? (1), Scopelogadus (1) and Lampanyctus (19) in the stomach of a female
adult Blainville's beaked whale (Mesoplodon densirostris) from southern Africa.
Mead (1989b) found trace quantities of squid beaks from three Blainville's
Sci. Rep. Cetacean Res.,
No. 1, 1990

48

NOJIMA

beaked whales and two Stejneger's beaked whales (M.stejnegeri) but no fish
remains were found in the stomachs. Concerning the ginkgo-toothed beaked
whale (M.ginkgodens), another Mesoplodon species observed in the present
study, no information on their food habits appears to be available.
A small amount of ossification in the attachments of the TC was seen in all
the Mesoplodon species observed. Because of the scarcity of published data on
the food habits of Mesoplodon spp., it is unknown whether these whales feed ona larger proportion of fish than do the Baird's beaked whale and Cuvier's
beaked whales, in which ossification in the TC does not occur at all. Mead(1989b) supposes that Mesoplodon species prefer mesopelagic squid and fish.
Benjaminsen and Christensen (1979) examined the stomach contents of 46
bottlenose whales (Hyperoodon ampullatus) caught off Iceland and 108 caught
off Labrador. They found that squid was the main food. Fishes such as cusk
(Brosmius brosme), lumpsucker (Cyclopterus lumpus), redfish (Sebastes sp.)and halibut (Reinhardtius hippoglossoides) were also eaten by nearly 10% of theanimals off Iceland and about 50% off Labrador, respectively. However, fish
represented a small proportion of the total volume of stomach contents.
The conditions of the BT and BF of all the Ziphiidae observed indicatethat these whales are primarily squid-eaters, though there remains a problem ofsome ossification in the attachments of the TC of the Mesoplodon species.

Platanistidae
Reeves and Brownell (1989) reviewed feeding habits of the susu (Platanista).
Among prey items found in the stomachs of susus, prawns, clams, catfishes(Wallago attu and Macrones aor), carp (Catla buchanami) and goby (Glossogobius giuris) appear to be their main food. In the close species to above
fishes, the meat of carp (Cyprinus carpio) and catfish (Silurus asotus) contain no
viamin D, and that of goby (Acanthogobius flavimanus) only contains the vitamin of 10 IU per 100g (Kagawa, 1989).
Boto (Inia geoffrensis) is known to feed on over 43 species of fish,
especially on sciaenids, cichlids and characins (Best and da Silva, 1989).
Leatherwood and Reeves (1983) and Evans (1987) mentioned that the dolphin
also feeds on armored catfish, and perhaps molluscs and crustaceans. The botoobserved in this study had been kept at a aquarium for two years and had been
fed exclusively on the Japanese horse mackerel (Trachrus japonicus) (Tobayama
and Kamiya, 1989) with low vitamin D content (Kagawa, 1989). Ossification in
the FC and TC probably does not occur either in the wild botos that are feedingon prey items low in vitamin D content.
According to Brownell's (1989) review on prey items of franciscana (Pontoporia blainvellei), the dolphins feed on many species of fish and some speciesof squid and shrimp. Among a wide variety of fishes as food for the dolphins,
the most important species was Cynoscion striatus (Sciaenidae) in the studies
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

49

examined in southern Brazilian and northern Uruguayan waters. Penaeid
shrimp of three species were found in the stomachs of dolphin. Squid beaks,
Loligo sanpaulensis, were commonly found in the stomachs of dolphins, and thesquid was one of the most important prey item for the dolphin in Bahia Samboromdon. The importance of squis as food for the dolphin appears to remain
an open question. Although the vitamin D content in most species of sciaenids
including the important species, C.striatus, and other bottom-dwelling fishes
listed in the review are unknown, bottom-dwelling fishes on the whole are of
low vitamin D content. The vitamin is not contained at all in fish meat ofAmmodytes personatus, Platycephalus indicus, Paraplagusia japonica, Salangichthys microdon, Lampetra mitsukurii, Trachurus japonicus and Conger
myriaster, and is contained only 8 ~ 20 IU per lOOg in fish meat of Acanthopagrus schlegeli, Acanthogobius fiavimanus and Sillago japonica (Kagawa,1989).

Monodontidae
According to a review of prey items on narwhals (Monodon monoceros) by Hay
and Mansfield (1989), the narwhal mainly feeds on the Arctic cod (Boreogadus
saida), the polar cod (Arctogadus glacialis), the Greenland halibut (Reinhardtius hippoglossoides), the squid (Gonatus fabricii) and the shrimps (Pasiphaea
tarda and Hymenodora glacialis). Finley and Gibb (1982) found abundant squid
beakes besides a number of cod (above spp.) in the stomachs of 73 nar\Vhals.
Among the fishes eaten by narwhals, the liver oil of halibut (Hippoglossus
hippoglossus) contains a large amount of vitamin D, although the value vary
according to seasons (550~20,000 IU/g). It is unknown whether the poorly
ossified process (might be present) in the animal observed was caused byingested halibuts.
Delphinidae
The genus Stenella feeds mainly on a wide variety of epipelagic and mesopelagic
fishes and a substantial amount of squid (Gaskin, 1982; Evans, 1987). Amongfish species, myctophids predominated in stomachs of S.longirostris (Fitch and
Brownell, 1968), S.coeruleoalba (Wilke, Taniwaki and Kuroda, 1953; Miyazaki,
Kusaka and Nishiwaki, 1973) and S.clymene (Perrin, Mitchell, Mead, Caldwelland van Bree, 1981), and they were also important to S.graffmani (Fitch and
Brownell, 1968). S.attenuata mainly feeds on epipelagic fishes such as flying fish
(Mitchell, 1975).
In the skulls of elderly spotted dolphins, in which the BF and BT arecomplete, the inner surface of the calvaria is roughened by many laminations
formed by ossification in the dura mater. This is considered to be caused byhyperplasia of the bones.
According to Evans (1987) and Mitchell (1975), the genera Delphinus,
Sci. Rep. Cetacean Res.,
No. 1, 1990

50

NOJIMA

Steno, Tursiops, Lagenorhynchus, Sousa, Lissodelphis and Lagenodelphis feedon a wide variety of epipelagic and mesopelagic fishes as well as squid and othermolluscs.
The percentage of fish and squid in the stomachs of bottlenose dolphinsand Pacific white-sided dolphins (Lagenorhynclus obliquidens) caught in waters
adjacent to Kyushu, Japan, during 1968-1969, were reported by the Research
Department Fisheries Agency, Japan (1969). Although stomach contents ofcatches varied a little according to different localities and different seasons,these dolphins had fed mainly on epipelagic and bottom-dwelling fishes, and thepercentage of squid was only 15-30% in the bottlenose dolphin and less than
40% in the white-side dolphin.
According to Baker (1981), Torres and Aguayo (1979) found 1,261 lanternfish otoliths and 46 squid beaks in the stomach of one southern right whale
dolphin (Lissodelphis peronii).
Nishiwaki and Randa (1958) reviewed the published reports of thestomach contents of 567 killer whales ( Orcinus area) caught in the coastal
waters off Japan from 1948 to 1957. Although the killer whale eats other warmblooded animals, most stomachs of the animals contained a large amount offishes such as cod, flatfish, sardine, salmon and tuna as well as squid. In theyounger animals, the intake ratio of fish was higher than those of adults.
Macintyre (1934) described that the killer whale is an important predator of
the salmon.
Nishiwaki (1965) described that the captive Risso's dolphin showed little
interest in any food except squid. According to Evans (1987), squid and octopus
are main foods of the Risso's dolphin, but fish is occasionally taken. No fish was
found in any Risso's dolphins in a study in Washington State (Stroud, 1968).
Poorly ossified BF and BT of the Risso's dolphins observed also suggest that
this species is primarily a squid-eater.
On the whole, the correlation between the degrees of ossification in the FC
and TC and known food items of cetaceans agrees with the hypothesis in thisstudy. However, there are several species in which the data do not support the
hypothesis, although the details of their feeding habits are not well known.
Pilot whale generally prefer squid. Sergeant (1962) observed the longfinned pilot whale (Globicephala melaena) feeding on short-finned squid (Illex
illecebrosus) almost exclusively during the July-October interval at Trinity Bay,
Newfoundland; cod was only taken when squid was scarce. He pointed out aclose relationship between the distribution of the pilot whale population off theeast coast of Newfoundland and that of the squid. He also quoted Kritzler's(1952) observations that a young captive short-finned pilot whale ( Globicephalamacrorhynchus) had refused to feed on fish at first, although it eventuallylearned to take them. Sergeant (1962) concluded that squid is the preferredfood of pilot whales, with fish as an alternative.
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

51

Keiver, Ronald and Draper (1988b) showed that plasma levels of 25-0HD,
24,25-(0H) 2D and calcium in the long-finned pilot whales (stranded, place andseason are not mentioned) were similar to those of nonmarine mammals, whilein the white whale (Delphinapterus leucas) and bottlenose dolphin (feeding
mainly on fish), levels of 25-0HD and 24,25-(0H) 2D were extremely high. The
results suggest that the long-finned pilot whale had fed mainly on squid (at least
during the time immediately preceding the stranding) and indicate high plasma
levels of vitamin D in fish-eating dolphins.
In this study, the long-finned pilot whale was not studied. If the animals
are truly squid-eaters, both the BF and BT should be absent according to myhypothesis. However, the BF and BT of the short-finned pilot whale, another
Globicephala species, and those of the false killer whale (Pseudorca crassidens)
and pygmy killer whale (Feresa attenuata), were ossified in the shape of theentire FC and TC. The stomach of a false killer whale caught off western Japan
contained 12 common sea basses Lateolabrax japonicus (about 60 cm in length)
as well as many squid beaks (the Research Department Fisheries Agency,
Japan, 1969). These whales may ingest much larger amounts of fish than isgenerally believed.

Phocoenidae
In the finless porpoise which feeds on small squid, cuttlefish and shrimp but also
takes small sandeels and other fishes (Mitchell et al., 1975), ossification in the
FC and TC (even in a lactating adult) has occurred much less frequently than inother phocoenids. Poorly developed BF and BT in these porpoises suggest thatthey feed mainly on crustaceans and molluscs or that fishes eaten have a low
vitamin D content. The meat of sandeel Ammodytes personatus contains novitamin D (Kagawa, 1989).
The harbor and Dall's porpoises feed on a large number of fish species.
Rae (1965) reviewed food habits of the harbor porpoise reported in an earlier
time in the North Sea, and more recently in the Baltic Sea (Lindroth, 1962), offeastern Canada (Sergeant and Fisher, 1957) and off Scotland by Rae himself.
The stomach contents showed that the harbor porpoise feeds mainly on fishes
such as clupeoids, gadoids and pleuronectids such as herring, whiting andmackerel, but squid were occasionally found in the stomachs in some quantity.
Smith and Gaskin (1974) examined stomach contents of P.phocoena taken fromcoastal waters of New Brunswick, Nova Scotia, and Prince Edward Island
during 1969-1972. The animals fed mainly on fishes such as herring, gadoids andmackerel, but squid was occasionally taken. Wilke and Nicholson (1958)
examined the stomachs of 86 truei-type and seven dalli-type Dall's porpoises(Phocoenoides dalli) collected off Japan, March to June 1952. Various myctophids formed 70%, by volume, of the stomach contents in the True's porpoises and 73% in the Dall's porpoises; the percentages of squid were 11 andSci. Rep. Cetacean Res.,No. I, 1990

52

NOJIMA

5%, respectively. Wilke et al. (1953) found that squid formed 98%, by volume,of the stomach contents in four Dall's porpoises taken from March to May off
northern Japan. This result contradicts Cowan's (1944) statement that Dall's
porpoise feeds exclusively on herring in the northern North Pacific.
In a previous study (Nojima, 1988) of the BF and BT of spotted dolphins, I
prepared the skulls very carefully so as not to damage the BF and BT. Whenossification of the BF and BT has not been completed, these are very fragile,especially the BT. It is likely that the BF and BT of all harbor and Dall's porpoises observed had been damaged during preparation of the skulls. I observed
no specimen in which the BT was complete, but the BF was relatively welldeveloped and the passage of the trigeminal nerve occurred as a round foramen
in most older specimens.
These porpoises probably ingest a large amount of fish, as has beenreported.

Consumption of Vitamin D by Fish-eating Dolphins
In the following section, the amounts of vitamin D that are taken by fish-eating
dolphins are estimated.
Sergeant (1969) examined feeding rates in captivity of nine dolphin
species. He estimated that of bottlenose dolphins to be 4.2 % body weight.
Nakajima (1973) also reported the average volume of daily food of a 300 kg
captive bottlenose dolphin as about 15 kg (mackerel Scomber japonicus).
The liver of a 410 g mackerel (Scomber japonicus) weighs about 10 g. If a
10 g mackerel liver is estimated conservatively to yield 1 g liver-oil (the averageliver-oil content of cod liver is more than 50%, by weight: Omura, Matsuura
and Miyazaki, 1942; although the values for fish vary according to season:
Pugsley, 1939), total vitamin Din 15 kg of mackerel can be estimated as at least
230,000 IU. This amount corresponds to about 120 times the recommended
daily dose for a human in weight-specific intake. With the exception of 1 a-OH-D
and 1 a, 25-(0H)iD, the active form of vitamin D used to treat humans forvitamin deficiencies, toxicity rarely results from an excessive intake of vitamins
D 2 and D 3 contained in food. However, a repeated intake of more than 100,000
IU per day of these vitamins may cause toxicity in humans (Krupp and Chatton,
1977; Kobayashi, 1989). Although the estimated vitamin D values taken by thedolphin do not approach the above dangerous level for humans in weightspecific intake, such large values cannot be ignored. Further consideration isneeded to extend this calculation to the wild dolphins, because of uncertainties
in the feeding rate (probably higher in the wild) and the consumption of variable food items with lower vitamin D values such as squids and many fish
species other than mackerel.
Keiver et al. (1988a) studied vitamin D metabolism in hooded seals (Cystophora cristata), which ingest large amounts of fish, as do dolphins of the genus
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

53

Stenella. They concluded that rapid conversion of vitamin D and a high capacityfor vitamin D storage in the large blubber mass appear to be factors in the resistance of seals to vitamin D toxicity. It is unknown whether similar factors
operate in the fish-eating cetaceans.
Concluding Remarks
Besides delphinids and phocoenids, I have observed the dolphin type BT only inspider monkeys (Ateles geoffroyi and A.paniscus) among all mammals studied,and in those species the BF was absent although the FC was identical with theTC histologically. The factors involved in ossification only in the TC are unknown. Most of the animals studied had been born and bred in a zoo and they
had been fed the usual diets, with no special items high in vitamin D. Formationof the dolphin type BT in spider monkeys cannot be related to their diet(Nojima, 1990b), and it obviously differs from those of delphinids andphocoenids in which ossification occurs in both the FC and TC.
Although I have not systematically examined hyperplasia of bones andcalcium deposition in soft tissue (which may occur in the fish-eating mammals),the degree of ossification in the FC and TC of cetaceans obviously proceeds inparallel with the increased proportion of fish in the diet.
Stomach contents provide direct evidence of the food eaten by an animal.
However, they do not necessarily reveal much about its longterm diet.
Although many cetaceans have been described as opportunistic feeders,the degree of ossification in their FC and TC appears to reflect the general trendof their food habits throughout life in the same way that the growth layers
formed in the teeth and ear plugs of cetaceans indicate their ages. A comparisonof the degrees of ossification in the FC and TC between captive dolphins fed
mainly squid and others fed mainly fish would provide a further test of thishypothesis.

Recommended Preparation Procedures
As already mentioned in the text, the BF and BT of delphinids and phocoenids
are fragile during preparation, especially when ossification has not been completed in the shape of the entire FC and TC. Therefore, close attention shouldbe paid to preparation of the skulls. Boiling the skull is not recommended
because the incomplete BF and BT are often fractured owing to strong contraction of the FC and TC by heat. Furthermore, the BF and BT are easily damaged
when the brain and its membranes are extracted through the foramen magnum.
In order to keep the BF and BT complete during preparation of the skulls, it isbest to ensure that the head (after removing the soft tissue as completely as
possible) is submerged in fresh water for several months, or until the brain andits membranes have completely rotted and can be washed away.
Sci. Rep. Cetacean Res.,No. I, 1990

54

NOJIMAACKNOWLEDGMENTS

I wish to express sincere gratitude to Dr N. Miyazaki and Dr M. Yoshiyuki,
Department of Zoology, National Science Museum, Tokyo, for giving meaccess to the valuable collections, and to Dr M. Nakajima, Izu-Mito Sea
Paradise, Shizuoka, who supplied me with materials and useful information. My
sincere thanks are also due to Dr K. Shigemasa, Department of Anatomy,
Nihon University School of Dentistry, Tokyo, who kindly helped me to collectreferences. I particulary thank Dr T. Kasuya and two anonymous reviewers fortheir comments on the manuscript. One of the two reviewers is greatly acknowledged for his kindly check of English style and grammar. I want to add a few
words of gratitude to my wife Miwa for her help in all respects throughout thisstudy.
REFERENCESBAKER, A. N. 1981. The southern right whale dolphin Lissodelphis peronii (Lacepede) in Australasian waters.
Nat. Mus. N.Z. Ree. 2(4): 17-34.
BALCOMB, K. C. 1989. Baird's beaked whale Berardius bairdii Stejneger, 1883: Arnoux's beaked whale Berardius arnuxii Duvernoy, 1851. pp. 261-288. In: S.H. Ridgway and R.J. Harrison (eds) Handbook of
Marine Mammals, vol. 4. Academic Press, London. 442pp.
BENJAMINSEN, T. and CHRISTENSEN, I. 1979. The natural history of the bottlenose whale, Hyperoodon ampullatus (Forster). pp. 143-164. In: H.E. Winn and B.L. Olla (eds) Behavior of Marine Animals, vol. 3:
Cetaceans. Plenum Press, New York. 438pp.
BEST, R.C. and da SILVA, V.M.F. 1989. Amazon river dolphin, boto Inia geoffrensis (de Blainville, 1817).
pp. 1-23. In: S.H. Ridgway and R.J. Harrison (eds) Handbook of Marine Mammals, vol. 4. Academic
Press, London. 442pp.
BOUILLON, R., VANKERKHOVE, P. and De MooR, P. 1976. Measurement of 25-hydroxyvitamin D 3 in serum.
Clin. Chem. (Winston-Salem, NC) 22: 364-368.
BROWNELL, R. L. 1989. Franciscana Pontoporia blainvillei (Gervais and d'Orbigny, 1844). pp.45-67. In: S.H.
Ridgway and R.J. Harrison (eds) Handbook of Marine Mammals, vol. 4. Academic Press, London.
442pp.
CLARKE, R. 1956. Sperm whales of the Azores. Discovery Rep. 28: 237-298.
CLARKE, M. R. 1980. Cephalopoda in the diet of sperm whales of the southern hemisphere and their bearing
on sperm whale biology. Discovery Rep. 37: 1-324.
CLARKE, M. R. 1986. Cephalopods in the diet of odontocetes. pp.281-321. In: M. M. Bryden and R.J. Harrison (eds) Research on Dolphins. Clarendon Press, Oxford. 478pp.
COBURN, J. W., HARTENBOWER, D.L. and NORMAN, A. w. 1974. Metabolism and action of the hormone vitamin D: Its relation to diseases of calcium homeostasis. Western J. Med. 121: 22.
CORBET, G. B. and HILL, J.E. 1986. A World List of Mammalian Species. Facts On File Publications, New
York. 254pp.
CowAN, I. M. 1944. The Dall porpoise, Phocoenoides dalli (True) of the northern Pacific Ocean. J. Mammal.
25: 295-306.
DELUCCA, H.F. 1974. Vitamin D: 1973. Am. J. Med. 57: 1.
DoYLE, P. T. 1987. Supplements other than forages. pp.429-464. In: J.B. Hacker and J.H. Ternouth (eds)
The Nutrition of Herbivores. Academic Press, Sydney. 552pp.
EVANS, P. G. H. 1987. The Natural History of Whales and Dolphins. Christopher Helm, London. 343pp.
FINLEY, K. J. and GrnB, E. J. 1982. Summer diet of the narwhal (Monodon monoceros) in Pond Inlet, Northern Baffin Island. Can. J. Zoo!. 60: 3353-3363.

Sci. Rep. Cetacean Res.,No. I, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

55

FITCH, J.E. and BROWNELL, R. L. 1968. Fish otoliths in cetacean stomachs and their importance in interpreting
feeding habits. J. Fish. Res. Bd Can. 25(12): 2561-2574.
FITCH, J.E. and BROWNELL, R. L. 1971. Food habits of the franciscana Pontoporia blainvillei (Cetacea:
Platanistidae) from South America. Bull. Mar. Sci. 21(2): 626-636.
FRASER, D.R. 1975. Advances in the knowledge of metabolism of vitamin D. Proc. Nutr. Soc. 34: 139.
GASKIN, D.E. 1976. The evolution, zoogeography and ecology of Cetacea. Oceanogr. Mar. Biol. Ann. Rev.
14: 247-346.
GASKIN, D.E. 1982. The Ecology of Whales and Dolphins. Heinemann Educational Books Ltd., London.
459pp.
HALE, H.M. 1947. The pigmy sperm whale (Kogia breviceps, Blainvelle) on South Australian coasts. Ree. S.
Aust. Mus. 8: 531-546.
HAY, K. A. and MANSFIELD, A. W. 1989. Narwhal Monodon monoceros Linnaeus, 1758. pp.145-176. Jn: S.H.
Ridgway and R.J. Harrison (eds) Handbook of Marine Mammals, vol. 4. Academic Press, London.
442pp.
HEYNING, J.E. 1989. Cuvier's beaked whale Ziphius cavirostris G.Cuvier, 1823. pp.289-308. In: S.H.
Ridgway and R.J. Harisson (eds) Handbook of Marine Mammals, vol. 4. Academic Press, London.
442pp.
HIRANO, T. 1982. Vitamin. p.251. In: Editorial Committee of the 8th Open Lecture of Tokyo Fishing College(ed.) Livelihood and fish. Seizando, Tokyo. 381pp. (in Japanese).
HoLMES, A. D., TRIPP, F. and SATTERFIELD, G. H. 1941. Fish liver and body oils: Chemical characteristics,
physical properties, and vitamin content. Ind. Eng. Chem. 33: 944-949.
HORWOOD, J. W. 1987. The sei whale: Population Biology, Ecology and Management. Croom Helm, London,
New York and Sydney. 375pp.
INAGAKI, N. 1970. Vitamin. pp.36-43. In: H. Toshikawa (ed.) Handbook of nutrition (Popular Medicine,
special issue 1). Nihonhyoronsha, Tokyo. 180pp. (in Japanese).
ISHII, M. 1973. Dictionary of Nutrition pp.262-263. Ishiyaku Shuppan, Tokyo. 458pp. (in Japanese).
JoNES, R. E. 1981. Food habits of smaller marine mammals from northern California. Proc. Calif. Acad. Sci.
42: 409-433.
KAGAWA, A. (ed.) 1989. Standard Tables of Food Composition in Japan (by Resources Council, Science andTechnology Agency, Japan). Kagawa Nutrition College, Tokyo 368pp.
KAWAKAMI, T. 1976. Squids found in the stomach of sperm whales in the northwestern Pacific. Sci. Rep.
Whales Res. Inst., Tokyo 28: 145-151.
KAWAKAMI, T. 1980. A review of sperm whale food. Sci. Rep. Whales Res. Inst., Tokyo 32: 199-218.
KAWAMURA, A. 1970. Food of sei whale taken by Japanese whaling expeditions in the Antarctic season 1967/
68. Sci. Rep. Whales Res. Inst., Tokyo 22: 127-152.
KAWAMURA, A. 1973. Food and feeding of sei whale caught in the waters south of 40° Nin the North Pacific.
Sci. Rep. Whales Res. Inst., Tokyo 25: 219-236.
KAWAMURA, A. 1977. On the food of Bryde's whales caught in the South Pacific and Indian Oceans. Sci. Rep.
Whales Res. Inst., Tokyo 29: 49-58.
KAWAMURA, A. 1980. A review of food of balaenopterid whales. Sci. Rep. Whales Res. Inst., Tokyo 32: 155197.
KAWAMURA, A. 1982. Food habits and prey distributions of three rorqual species in the North Pcific Ocean.
Sci. Rep. Whales Res. Inst., Tokyo 34: 59-91.
KEIVER, K. M., DRAPER, H. H. and RONALD, K. 1988a. Vitamin D metabolism in the hooded seal ( Cystophoracristata). J. Nutr. 118: 332-341.
KEIVER, K. M., RoNALD, K. and DRAPER, H. H. 1988b. Plasma levels of vitamin D and some metabolites inmarine mammals. Can. J. Zoo/. 66: 1297-1300.
KOBAYASHI, T. 1989. Vitamin D. pp. 31-48. In: The Vitamin society of Japan (ed.) Vitamin Handbook. vol.
1, Kagakudojin, Kyoto. 127pp. (in Japanese).
KRITZLER, H. 1952. Observations on the pilot whale in captivity. J. Mammal. 33: 321-334.
KRUPP, M.A. and CHATTON, M.J. (eds) 1977. Current Medical Diagnosis and Treatment. Lange Medical
Publications, California. Japanese translation published by Maruzen, Tokyo in 1977. 1071pp.
KuRE, K. and SAKAMOTO, T. 1966. Avitaminosis D. pp.52-57. In: S. Okinaka (ed.) Internal Medicine. vol. 2,
Nanzando, Tokyo. 818pp. (in Japanese).

Sci. Rep. Cetacean Res.,
No. 1, 1990

56

NOJIMA

LEATHERWOOD, S. and REEVES, R. 1983. Sierra Club Handbook of Whales and Dolphins. Sierra Club Books,
San Francisco. 302pp.
LINDROTH, A. 1962. Baltic salmon fluctuations 2: Porpoise and salmon. Rep. Inst. Freshwat. Res. Drottningholm. 44: 105-112.
MACINTYRE, D. 1934. Sea enemies of salmon. Salm. Trout Mag. 74: 38-42.
MATSUURA, Y. 1942. On the Northern Porpoise Whale, Berardius bairdii Stejneger in the adjacent waters of"Bosyu". Zoo[ Mag., Tokyo 54: 466-473. (in Japanese).
MEAD, J. G. and PAYNE, R. S. 1975. A specimen of the Tasman beaked whale, Tasmacetus shepherdi, from
Argentina. J. Mammal. 56: 213-218.
MEAD, J. G. 1981. First records of Mesoplodon hectori (Ziphiidae) from the northern hemisphere and a
description of the adult male. J. Mammal. 62: 430-432.
MEAD, J.G. 1989a. Bottlenose whales Hyperoodon ampullatus (Forster, 1770) and Hyperoodon planifrons
Flower, 1882. pp.321-348. In: S.H. Ridgway and R.J. Harrison (eds) Handbook of Marine Mammals,
vol. 4. Academic Press, London. 442pp.
MEAD, J. G. 1989b. Beaked whales of the genus Mesoplodon. pp.349-430. In: S.H. Ridgway and R.J.
Harrison (eds) Handbook of Marine Mammals, vol. 4. Academic Press, London. 442pp.
MITCHELL, E. (ed.) 1975. Review of biology and fisheries for small cetaceans. J. Fish. Res. Bd Can. 32:
889-983.
MIYAZAKI, N., KusAKA, T. and N1sHIWAKI, M. 1973. Food of Stenella coeruleoalba. Sci. Rep. Whales Res.
Inst., Tokyo 25: 265-275.
M1zuE, K. 1951. Food of whales. Sci. Rep. Whales Res. Inst., Tokyo 5: 81-90.
NAGORSEN, D. W. and STEWART, G. E. 1983. A dwarf sperm whale (Kogia simus) from the Pacific coast of
Canada. J. Mammal. 64(3): 505-506.
NAKAJIMA, M. 1973. A dolphin named Echo. Akaneshobo, Tokyo. 146pp. (in Japanese).
NAKAYAMA, K. 1975. Dose. pp.650-661. In: K. Nakayama (ed.) Pediatrics. Bunkodo, Tokyo 688pp. (inJapanese).
NEMOTO, T. 1957. Food of baleen whales in the northern Pacific. Sci. Rep. Whales Res. Inst., Tokyo 12:
33-89.
NEMOTO, T. 1959. Food of baleen whales with reference to whale movements. Sci. Rep. Whales Res. Inst.,
Tokyo 14: 149-290.
NEMOTO, T. 1962. Food of baleen whales collected in recent Japanese Antarctic whaling expeditions. Sci. Rep.
Whales Res. Inst., Tokyo 16: 80-103.
NEMOTO, T. and NAsu, K. 1958. Thysanoessa macrura as a food of baleen whales in the Antarctic. Sci. Rep.
Whales Res. Inst., Tokyo 13: 193-199.
NEMOTO, T. and Yoo, K. 1970. An amphipod, (Parathemisto gaudichaudii) as a food of the Antarctic sei
whale. Sci. Rep. Whales Res. Inst., Tokyo 22: 153-158.
NEMOTO, T. and KAWAMURA, A. 1977. Characteristics of food habits and distribution of baleen whales withspecial reference to the abundance of North Pacific sei and Bryde's whales. Rep. int. Whal. Commn(special issue 1): 80-87.
NERINI, M. 1984. A review of gray whale feeding ecology. pp.423-450. In: M.L. Jones, S.L. Swartz and S.
Leatherwood (eds) The gray whale Eschrichtius robustus. Academic Press, Florida. 600pp.
NisHIWAKI, M. and RANDA, C. 1958. Killer whales caught in the coastal waters off Japan for recent 10 years.
Sci. Rep. Whales Res. Inst., Tokyo 13: 85-96.
N1sHIWAKI, M. 1963. Taxonomical consideration on genera of Delphinidae. Sci. Rep. Whales Res. Inst., Tokyo
17: 93-103.
NrsHIWAKI, M. 1965. Whales and Pinnipeds. University of Tokyo Press, Tokyo. 439pp. (in Japanese).
NrsHIWAKI, M. and OGURO, N. 1971. Baird's beaked whales caught on the coast of Japan in recent 10 years.
Sci. Rep. Whales Res. Inst., Tokyo 23: 111-122.
NonMA, T. 1988. Developmental pattern of the bony falx and bony tentorium of spotted dolphins (Stenella
attenuata) and the relationship between degree of development and age. Mar. Mammal. Sci. 4:
313-322.
NonMA, T. 1989. Mairuka-ka no Kotsusei-dainokama to Kotsusei-shonotento no Keisei ni tsuite. [On the formation of the bony falx and bony tentorium of Delphinidae]. Geiken Tsushin, Whales Res. Inst., Tokyo
375: 9-14. (in Japanese).
Sci. Rep. Cetacean Res.,
No. 1, 1990

BONY FALKS AND BONY TENTORIUM OF WHALES

57

NoJIMA, T. 1990a. A morphological consideration of the relationships of Pinnipedia to other carnivorans
based on the bony tentorium and bony falx. Mar. Mamm. Sci. 6: 54-74.
NonMA, T. 1990b. Developmental pattern of the bony tentorium of spider monkeys (Ateles). Primates 31:
137-141.
0KUTANI, T. and NEMOTO, T. 1964. Squids as the food of sperm whales in the Bering Sea and Alaskan Gulf.
Sci. Rep. Whales Res. Inst., Tokyo 18: 111-122.
OMURA, H., MATSUURA, Y. and MIYAZAKI, I. 1942. [Whales - their science and practice of whaling].
Suisansha, Tokyo. 319pp. (in Japanese).
OMURA, H. 1958. North Pacific right whale. Sci. Rep. Whale Res. Inst., Tokyo 13: 1-52.
OMURA, H., 0HSUMI, S., NEMOTO, T., NAsu, K. and KASUYA, T. 1969. Black right whales in the North Pacific.
Sci. Rep. Whales Res. Inst., Tokyo 21: 1-78.
OWEN, R. 1866. On the Anatomy of Vertebrates. vol. 3, Reprinted in 1973, AMS Press, New York. 915pp.
PERRIN, W.F., WARNER, R.R., Fiscus, C.H. and HOLTS, D.B. 1973. Stomach contents of porpoise, Stenella
spp., and yellowfin tuna, Thunnus albacares, in mixed-species aggregations. Fish. Bull. 71: 1077-1092.
PERRIN, W. F., MITCHELL, E. D., MEAD, J. G., CALDWELL, D. K. and van BREE, P. J. H. 1981. Stenella clymene,
a rediscovered tropical dolphin of the Atlantic. J. Mammal. 62(3): 583-598.
PIKE, G. C. 1950. Stomach contents of whales caught off the coast of British Columbia. Prag. Rep. Pacif. Cst.
Stns. 83: 27-28.
PIKE, G. C. 1962. Migration and feeding of the gray whale (Eschrichtius gibbosus). J. Fish. Res. Bd Can.
19(5): 815-838.
PINEDO, M. C. 1987. First record of a dwarf sperm whale from southwest Atlantic, with reference to osteology,
food habits and reproduction. Sci. Rep. Whales Res. Inst., Tokyo 38: 171-186.
PUGSLEY, L. I. 1939. Vitamin A and D potencies of liver and intestinal oils of halibut. J. Fish. Res. Bd Can. 4:
396-404.
RAE, B.B. 1965. The food of the common porpoise (Phocaena phocaena). J. Zool. 146: 114-122.
RAUN, G.G., HOESE, H.D. and MosELEY, F. 1970. Pygmy sperm whales, genus Kogia, on the Texas coast.
Tex. J. Sci. 21: 269-274.
REEVES, R.R. and BROWNELL, R. L. 1989. Susu Platanista gangetica (Roxburgh, 1801) and Platanista minor
Owen, 1853. pp.69-99. In: S.H. Ridgway and R.J. Harrison (eds) Handbook of Marine Mammals,
vol. 4. Academic Press, London. 442pp.
Research Department Fisheries Agency, Japan, 1969. [Reports on investigation of fishery damage by small
toothed whales in western waters of Japan during 1967-68.] 108pp. (in Japanese).
RICE, D. W. 1963. Progress report on biological studies of the larger Cetacea in the waters off California.
Norsk Hvalfangst-Tid. 52(7): 181-187.
RoE, H.S.J. 1969. The food and feeding habits of the sperm whales (Physeter catodon, L) taken off the west
coast of Iceland. J. Cons. Int. Explor. Mer. 33: 93-102.
Ross, G.J.B. 1978. Records of pygmy and dwarf sperm whales, genus Kogia from Southern Africa, withbiological notes and some comparisons. Cape Prov. Mus., Nat. Hist. 11: 259-327.
Ross, G.J.B. 1984. The smaller cetaceans of the south east coast of southern Africa. Ann. Cape. Prov. Mus.,
Nat. Hist. 15: 173-410.
SCHULTZE, 0. and LuBoscH, W. 1935. Atlas und kurzgefasstes Lehrbbuch der topographischen undangewandten Anatomie. (Japanese translation by Nishi, S., 1941. Marzen Co., Tokyo, 353pp.)
SERGEANT, D.E. and FISHER, H.D. 1957. The smaller cetacea of eastern Canadian waters. J. Fish. Res. Bd
Can. 14: 83-115.
SERGEANT, D. E. 1962. The biology of the pilot or pot-head whale Globicephala melaena (Traill) in Newfoundland waters. Bull. Fish. Res. Bd Can. 131: 1-84.
SERGEANT, D. E. 1969. Feeding rates of Cetacea. FiskDir. Skr. Ser. HavUnders. 15: 246-258.
SMITH, G.J.D. and GASKIN, D.E. 1974. The diet of harbor porpoise (Phocoena phocoena (L.)) in coastal
waters of Eastern Canada, with special reference to the Bay of Fundy. Can. J. Zoo!. 52: 777-782.
STROUD, R. K. 1968. Risso dolphin in Washington State. J. Mammal. 49: 347-348.
ToBAYAMA T. and KAMIYA, T. 1989. Observations on Inia geoffrensis and Platanista gangetica in captivity at
Kamogawa Sea World, Japan. pp.42-45. In: W.F. Perrin, R.L. Brownell, Jr., Zhou Keiya and Lin
Jiankang (eds) Biology and conservation of the river dolphins. (IUCN Species Survival Commission
Occasional Papers No.3) IUCN Publications Services Unit, Cambreidge. vi + 173pp.
Sci. Rep. Cetacean Res.,
No. 1, 1990

58

NOJIMATORRES, D. N. and AGUAYO, L. A. 1979. Habitors alimentaries de Lissodelphis peronii en Chile central(Cetacea: Delphinidae). Revista de Biologia Marina 16(3): 221-224.
WILKE, F., TANIWAKI, T. and KURODA, H. 1953. Phocoenoides and Lagenorhynchus in Japan with notes on
hunting. f. Mammal. 34: 488-497.
WILKE, F. and NICHOLSON, A. J. 1958. Food of porpoises in waters off Japan. f. Mammal. 39(3): 441-443.
WoLMAN, A.A. 1989. Gray whale Eschrichtius robustus (Lilljeborg, 1861). pp.67-90. In: S.H. Ridgway and
R.J. Harrison (eds) Handbook of Marine Mammals, vol. 3. Academic Press, London. 362pp.

EXPLANATIONS OF PLATESPLATE I.
Lateral view of the skull and head of adult spotted dolphins.
Fig. 1. BF: bony falx, BT: bony tentorium, U 1: unossified portion for the passage of thecerebral veins into the dorsal sagittal sinus, U 2 : unossified portion for the passage ofthe continuation of the spinal meningeal artery (SMA), G: groove for the continuation of SMA.
Fig. 2. FC: falx cerebri, TC: tentorium cerebelli, SMA: continuation of the SMA(intradural).
PLATE II.
Fig. 1. Inner surface of the cranial cavity of a juvenile spotted dolphin. DSS: dorsal
sagittal sulcus.
Fig. 2. Lateral view of the skull of a young striped dolphin. The BF and BT have notbeen completed as a continuous bony plate. Black arrows point to the edges ofdeveloping BT.
PLATE III.
Interior of the posterior half of the cranial cavity of an elderly spotted dolphin. Arrows
indicate ossified laminations. FM: foramen magnum.

Sci. Rep. Cetacean Res.,
No. 1, 1990

6~

0
6
6
!［
＇ ・ON
・
Si!U U
V
i
i
:
J
V
J
i
l
:
J ・diiU ・
！
:
J
S

Iヨ
工.V!d
Sヨ！VHMdOl
ぺ凡 nIO.LN
ヨ.
L人NOHONVS)f!Vd入NOH

60

NOJIMA

PLATEI
I
.

S
c
i
.R
e
p
.C
e
t
a
c
e
a
nR
e
s
.
,
No.I
,1990

1
9

0661 '['ON"SJ~ UViJ:llJIJ:) · da~ ・1:1s

・m3lV'1dS
ヨTv'HM.
'.
:10l
ぺ凡nIOlN
ヨi 入NOSON¥i$
)
1
1¥
i
.
c
l入NOS