Abstract
The comparative study o n the morphological characters of the mandible in Norma lateralis was made in 78 species of mammals. In the present investigation, special attention was paid of the relation of mandibular shape to food habit.
(1) All mammals can be divided into two groups according to the mandibular shape: the first group comprises Carnivora, Chiroptera, Insectivora, and Zoophaga of Marsupialia, and the second group, Ungulata, Rodentia, Lagomorpha, Primates, Proboscidea, and Phytophaga of Marsupialia.
(2) The characteristics of the first group consisted of large coronoid process, well-developed masseteric fossa, styloid angular process, short condyloid process, and canoe-shaped body, while the second group is characterised by small or slender coronoid process, small and shallow massecteric fossa, absence of the angular process (except rodents), tall condyloid process, and tapering body with slight modifications.
(3) In view of the food habit, the first group is animal-eating (except Megachiroptera), and the second, plant-eating. Therefore, the author calls the former “ Zoophagous Group ” and the latter “ Phytophagous Group ”. It is suggested that Megachiroptera may have lately changed its alimentation from insectivorous to frugivorous style.
