Monachus tropicalis Gray, 1850

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 : 262-263

Monachus tropicalis Gray, 1850 ( fig. 5 ; table 1)

The mandibular ramus does not strongly project dorsally and is broader than the body. The condyloid process is situated slightly superior to the alveolar border of the mandible. The condyloid process is approximately at the level of the mandibular notch and is directed more posteriorly than vertically, yielding a rather deep mandibular notch. The condyloid process in males has a distinct crest and a well-defined masseteric fossa ( fig. 5 ). The posterior edge of the coronoid process is to some extent directed toward the condyloid process, more so in males. The coronoid process is a large broad triangle with a markedly round apex located superior to the condyloid process. On the lingual surface of the coronoid process is a well-defined depression that marks the site of attachment of some temporalis muscle fibers. Additional attachment is provided by a small overhang on the labial surface of the coronoid process. There is a slight angular process at the mandibular angle. The condyloid angle (♀ 16°; table 1) is significantly smaller than that of cystophorines and phocines, suggesting smaller gape.

It is difficult to determine how far down the inferior border of the masseteric fossa extends, but it appears to cover the entire length of the ramus ( fig. 5 ). The fossa width measures about 5.0 cm and indicates a relatively well-developed masseter muscle. The surface within the fossa is rather smooth and is not marked by ridges or grooves for masseter tendon attachment. The height of the coronoid process height is 3.0 cm and the width is

Рис. 5. Подсемейство Monachinae : челюсть Monachus tropicalis , вид с губной стороны (♀, справа, NMNH 100362); показана жевательная ямка (пунктирная линия).

4.0 cm, providing a large surface area for the attachment of temporalis muscle fibers.

Very little is known about the natural diet of the extinct Caribbean monk seals ( Monachus tropicalis ), but they likely exhibited a generalized feeding strategy similar to most phocids (Adam, 2004). Presumably, the diet was similar to Monachus monachus and M. shauinslandi , the two species of monk seals that are still alive today. Evidence from stomach contents and fecal deposits reveal that monk seals feed primarily on lobster, eels, larval fish and octopus ( Kenyon, 1981). It has been noted that monk seals can dive up to about 615 m, but the estimated preferred feeding niche is less than 100 m ( Kenyon, 1981). Studies of Monachus schauinslandi (Hawaiian monk seals) show that the average diving depth is 10–40 m, with maximum ranging from 121–175 m ( Kooyman et al., 1983).

Figures

Fig. 5. Subfamily Monachinae: mandible of Monachus tropicalis in labial view (♀, right, NMNH 100362); showing masseteric fossa (dashed outlines).