Comparative Morphology of the Mammalian Mandible in Relation to Food Habit

Abstract

The findings described above are summarised in Table 1. It is easily understood that animals studied can be divided into two groups : the first group includes Carnivora, Chiroptera, Insectivora, and Zoophaga of Marsupialia ; and the second group includes Ungulata, Rodentia, Lagomorpha, Primates, Proboscidea, and Phytophaga of Marsupialia. The mandibles of the first group are possessed of the following characters : (1) canoe-shaped mandibular body, (2) large triangular coronoid process, (3) large well-developed masseteric fossa which spreads over entire surface of the ramus, (4) presence 9f the angular process on the mandibular angle, and (5) short condyloid process in relation to the occlusal plane. On the other hand, the characteristics of the second group consist in : (1)- flat and rough-surfaced ramus, (2) the mandibular body tapering toward the symphyseal part, (3) small and shallow masseteric fossa limited to the upper portion of the ramus, (4) small, or slender coronoid process which is in some forms (ruminants) fairly long and strongly curved posteriorly, and (5) tall condyloid process in relation to the occlusal plane of the molars. In regard to the food habit, the first group is animal-eating (carnivorous or insectivorous), except Megachiroptera (frugivorous), while the second group is plant-eating (herbivorous or frugivorous). The first group should be named generically “Zoophagous Group” and the second “Phytophagous Group”. Consequently it becomes clear that the mandible of animal-eating mammals is uniformly possessed of a set of particular characters, whereas in the mandible of plant-eating mammals, another set of characters is found beyond the taxonomic differences. It must be noted that variations are greater amony Phytophagous Group than among Zoophagous Group. As far as the shape of the mandible is concerned, no special character common to omnivorous forms can be picked up. The Mandibles of some omnivorous forms can be without dispute classified into Zoophagous Group (bear, racoon, coati, badger, racoon dog, fox, marten, etc.) and others into Phytophagous Group (non-ruminants, primates, and rats). © 1971, Editorial Board of Okajimas Folia Anatomica Japonica. All rights reserved.