Comparative morphological peculiarities of the skulls at some rodents (rabbit, nutria, guinea pig and squirrel)

Abstract

Generally, the rodent skulls have a rectangular shape, viscerocranium being about 2/3 of its length, representing the dominant portion of the skull. As a result of studies performed on the skulls from rabbit, guinea pigs, squirrels and nutria, several differences are observed in the matter of skulls morphology which is determined primarily by grasping and trituration of the food, even though these animals are rodents. At all rodents, the incisive bones are dominant, having a strongly rostral curved aspect. The convexity continues with the incisors, in their turn highly curved and strong. In rabbits, the jointing condyle is highly exalted above the mandible molar level which reduces the sectioning force through vertical action and its jointing surface is transversally orientated, allowing the flexion, extension or the propulsion and the caudal movements, like all herbivores. Articular condyle in nutria exceeds about 1 cm the surface of the mandible molars plane, this species requires an increased force for severing food, both in the terrestrial or aquatic environment. In guinea pigs, a terrestrial species, the condyle jointing surface is located near the molar level easing the food trituration by vertical and lateral movement. At squirrel, the condyle is placed nearly in the mandible molars plane but the ascension of the coronoid process above the molars plan eases the antero-caudal movements more than the vertical sectioning.