Halichoerus grypus Fabricius, 1791

Koretsky, I. A., Rahmat, S. J. & Peters, N., 2014, Remarks On Correlations And Implications Of The Mandibular Structure And Diet In Some Seals (Mammalia, Phocidae), Vestnik Zoologii 48 (3), pp. 255-268 : 260-261

Halichoerus grypus Fabricius, 1791 ( fig. 4 , A, table 1)

The mandibular ramus is noticeably thicker than the body. The condyloid process is approximately at the same level as the mandibular notch and has a large round head. On the anterior surface of the condyloid process is a well-defined depression for the attachment of the lateral pterygoid muscle. The coronoid process is a large broad triangle with a rounded apex located superior to the condyloid process. The posterior edge of the coronoid process ends as a strong vertical slope towards the mandibular notch. Along the posterior border of the ramus is a small inferior notch and a slight angular process. In H. grypus the condyloid angle of 20° (table 1) is considerably smaller than in most cystophorines.

The masseteric fossa is well defined with a width of about 5.5 cm and located in the inferior portion of the fossa are small oblique ridges for the attachment of superficial masseter tendons (black arrows in fig. 4 , A; similar to M. angustirostris ). These features are either less defined or absent in the fossa of the other species presented in this paper. The masseteric fossa is especially deep along both its anterior and posterior borders, where the ramus meets with the body. The coronoid process is quite broad and provides significant surface area for the attachment of temporalis muscle fibers. The taller coronoid process is located about 4.5 cm superior to the mandibular notch.

Gray seals ( H. grypus ) feed mostly on salmon, cod, herring, skates, squid and octopus (Bonner, 1981). The diving depth ranges from 70–225 m ( Scronce, Ridgway, 1980; Thompson et al., 1987).

Figures

Fig. 4. Subfamily Phocinae: А — mandible of Halichoerus grypus, left, NMNH 51488; in labial view showing masseteric fossa (dashed outline) and arrows indicating ridge for attachment of superficial masseter tendons; B —mandible of Phoca largha, right, reversed, NMNH 290654; in labial view showing width (w) and height (h) of the masseteric fossa and the small ridge on the coronoid process (black *) for attachment of the temporalis muscle.