OBSERVATION ON TWO MANDIBLESOF MESOPLODONMASAHARU NISHIW AKI
In 1958 the author reported the Mesoplodon ginkgodens as a new speciesof the Ziphioid whales. Yet not many comments on this report havebeen received. But some one might consider that, M. ginkgodens closely
resembles M. stejnegeri or M. bowdoini. On the other hand some may
be of the opinion that a sufficiently adequate series of specimens is notavailable to determine the limit of variation.
Now, the author has collected some mandibles of young Mesoplodon.
The collection is very interesting as an accumulation of adequate seriesof specimens.
Late in June, 1960, after the author send the specimen of Mesoplodon
stranded at the Akita Beach to the Whales Research Institute, he went
to Ayukawa for his routine work on whale investigation. Mr. Y. Kimura
was waiting for him in Ayukawa, and he regreted that the two whales
perhaps belonging to Mesoplodon which were caught in several days
ago, had not been preserved. When he went to the whaling station,
however, one pair of the mandibles of the whale (Ayukawa Mesoplodon
No. 2) and a left side mandible of the other whale (Ayukawa MesoplodonNo. 3) were found, but most of the bones had been already treated in
the cooker. These whales were caught by "Hachiryu-maru ", which isa catcher boat for small species whaling, at a point about 30 miles
southeast of Kinka-san within a few days. The whaling company reported
on both individuals as being a 15 feet long male Cuvier's beaked whale(Ziphius cavirostris). Measurements of these mandibles are shown inTable 1.
The body lengths of the whales as well as the mandibles have certainsimilarities in sizes. However the shape of the teeth and the position
where the teeth are situated give an impresion that they belong to adifferent species. Ayukawa Mesoplodon No. 3 has a tooth that closely
resembles that of the Ogawa specimen of M. ginkgodens (Nishiwaki &Kamiya, 1958). This tooth was under growth and the root is not completed as shown in Fig. 2 of Plate II.
The teeth of the Ayukawa Mesoplodon No. 2 are snaped at the part
where the teeth are inserted into the alveolae. This was caused byperhaps a worker trying to take out the teeth with a rod. The upper
half of the teeth were placed near the cooker for a few days. When79

M. NISHIWAKI80

the author went to the factory with Mr. Kimura, these pieces of theteeth had been already lost. Observation of the lower half of the teeth
showed that the roots were almost finished with the pulp cavity slightly
showing. From this point of view the specimen No. 2 may be considered
as slightly older than the specimen No. 3.
The author can not say whether the teeth have appeared from thegum or not. It seems that in the case of Physeter the teeth cut thegum when they reach sexual maturity, and in the most of the speciesof Delphinidae the teeth grown up from the gum when they reach theweaning period. It seems that in case these two individuals reach thesame age at about the same time, many differences on the teeth andTABLE 1.

MEASUREMENT OF THE MANDIBLES
Ayukawa No. 2(M. stejnegeri)

Serial No. of specimen
Length of mandible
Distance from anterior end of mandible
to coronoid process
Length of symphysis
Distance from anterior end of mandible
to anterior end of alveolus
Distance from anterior end of mandible
to posterior end of alveolus
Depth of mandible at posterior marginof toothMinimum depth of mandible between
tooth and coronoid process
Breath across mandiblar condyles
Distance from coronoid process to angle
Vertical length of tooth
Horizontal length of tooth
Breath of tooth (transverse)

Ayukawa No. 3(M. ginkgodens)

Left
702mm

Right709mm

Left
666 + mm (700)

685

687

648+ (682)

191

191

136+ (172)

152

150

92+ (130)

242

243

126+ (158)

76

74

67

63

63

61

345
116+, (138)112+, (132)

72869
7124
52
75
7

mandibular characteristics may appear. The author concludes that these
two specimens do not belong to the same species. The author received
the impression that the specimen No. 2 belongs to M. steJnegeri andthe specimen No. 3 is presumed as M. ginkgodons, though the available
data were scanty.
As result of the foregoing observations, it seems that some Ziphioid
whales, that belong to Mesoplodon, were caught as Ziphius cavirostrisin the past days at Ayukawa. The parties concerned in whaling shouldobserve the Ziphioid whales more carefully in the future in order toavoid the repetition of similar oversights.
The author is much indebted to Mr. Yoshinori Kimura for his constantkindness and support.

OBSERVATION ON TWO MANDIBLES OF MESOPLODON

81

REFERENCESFLOWER, W. H. (1878). A further contribution to the knowledge of the existing ziphioid
whales: genus Mesoplodon. Trans. Zool. Soc. London, X. part 11: 415-37.
MOORE, J. C. (1960). New Records of the Gulf-Stream Beaked Whale, Mesoplodon gervaisi,and Some Taxonomical Considerations. Amer. Mus. Nov. 1993.
NISHIWAKI, M. & T. KAMIYA (1958). A beaked whale Mesoplodon stranded at Oiso beach,
Japan. Sci. Rep. Whales Res. Inst., no. 13: 53-83.
- - - (1959). Mesoplodon stejnegeri from the coast of Japan. Sci. Rep. Whales Res.
Inst., no. 14: 35-48.
RAVEN, H. C. (1937). Notes on the taxonomy and osteology of two species of Mesoplodon(M. europaeus Gervais, M. mirus True). Amer, Mus. Nov. 905: 1-30.

82

M. NISHIW AKI

EXPLANATION OF PLATESPLATE I
Fig. 1 (Upper). Lateral views of mandibles. Upper two are Mesoplodon stejnegeriof Ayukawa specimen No. 2, and lower one is Mesoplodon ginkgodens ofAyukawa specimen No. 3.
Fig. 2 (Lower). Reversed lateral views of mandibles. Upper one is Mesoplonon
ginkgodens of Ayukawa specimen No. 3, and lower two are Mesoplodon stejnegeriof Ayukawa specimen No. 2.
PLATE II
Fig. 1. Dorsal views of mandibles. Left side one is left mandible of Mesoplodon
ginkgodens of Ayukawa specimen No. 3, and right side one that both sidebones are attached is Mesoplodon stejnegeri of Ayukawa specimen No. 2.
Fig. 2. Lateral and ventral views of teeth are shown in upper and lower lines
respectively. Left one is Mesoplodon ginkgodens of Ayukawa specimen No. 3and right side two are Mesoplodon stejnegeri of Ayukawa specimen No. 2 inboth lines.

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