Phoca largha Pallas, 1811

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 : 261-262

Phoca largha Pallas, 1811 ( fig. 4 , B, table 1)

The mandibular ramus is directed posterodorsally and the mandibular body is noticeably thinner than the body of Halichoerus grypus . The condyloid process is situated superior to the tooth row (similar to H. grypus ) and the mandibular notch. The coronoid process is a slender triangle with the apex sloping towards the condyloid process. The area of attachment for the temporalis muscle on the coronoid process is marked by a small ridge that is directed towards the labial side of the ramus (black asterisks in fig. 4 , B). Along the posterior border of the ramus is a small knob-shaped angular process. The condyloid angle of 25° is larger than H. grypus , but is smaller than the cystophorines C. cristata and female M. angustirostris .

The entire labial surface of the ramus is covered by the masseteric fossa ( fig. 4 , B), which is very smooth and devoid of ridges or grooves for attachment of masseter tendons.

Рис. 4. Подсемейство Phocinae : А — нижняя челюсть Halichoerus grypus , слева, NMNH 51488, вид с губной стороны; показана жевательная ямка (пунктирная линия), стрелки указывают на гребень для крепления поверхностных жевательных сухожилий; B — нижняя челюсть Phoca largha , справа, развернута, NMNH 290654, вид с губной стороны; показана ширина (w) и высота (h) жевательной ямки и малый гребень на венечном отростке (отмечены звёздочками) для прикрепления височной мышцы.

The fossa is much deeper along the anterior and posterior borders when compared to the shallower inferior border. The fossa width (3.0 cm) is noticeably narrower than in H. grypus , suggesting that the masseter is likely to be slightly smaller and weaker. The coronoid process height (about 1.8 cm) is smaller than the one of H. grypus . Along with the difference in height, the much narrower P. largha coronoid process apex indicates less attachment area for the temporalis muscle. The diminished sizes of the P. largha masseter and temporalis correspond to an overall smaller mandible than in H. grypus .

Spotted seals ( P. largha ) are mostly piscivorous, feeding on available fish including flounder, herring, anchovy, trout, salmon and others as well as squids, crabs and clams (Bigg, 1981; Dehn et al., 2006). The maximal dive depth for P. largha was thought to be 206 m ( Harrison, Kooyman, 1968; Kooyman, 1981), but it has been noted more recently that they can dive up to 508 m ( Schreer, Kovacs, 1997).

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.