EVIDENCE FOR RODENT-COMMON AND SPECIES-TYPICAL LIMB AND DIGIT USE IN EATING, DERIVED FROM A COMPARATIVE-ANALYSIS OF 10 RODENT SPECIES

Order Rodentia comprises a vast portion of mammalian species (1814 spe cies), which occupy extremely diverse habitats requiring very distinct motor specializations (e.g. burrowing, hopping, climbing, flying and swimming). Although early classification of paw use ability suggests r odents are impoverished relative to primates and make little use of th eir paws, there have been no systematic investigations of paw use in r odents. The present study was undertaken to describe limb/paw movement s in a variety of common rodents. The movements used for handling sunf lower seeds and other foods were videorecorded and analyzed in the gui nea pig (Cavia porcellus), Mongolian gerbil (Meriones unguiculatus), S yrian hamster (Mesocricetus auratus), laboratory mouse (Mus musculus), laboratory rat (Rattus norvegicus), gray squirrel (Sciurus carolinens is), red squirrel (Tamiasciurus hudsonicus), Richardson's ground squir rel (Spermophilus richardsonni), prairie dog (Cynomus parvidens), and Canadain beaver (Castor americanus). The results suggested five order- common movements of food handling: (1) locating food by sniffing, (2) grasping food by mouth, (3) sitting back on the haunches to eat, (4) g rasping the food using an elbow-in movement, and (5) manipulate the fo od with the digits. Different species displayed species-typical specia lizations including (1) bilateral grasping with the paws (gerbil), (2) unilateral grasping with a paw (beaver), (3) unilateral holding (grou nd squirrels), (4) various grip and digit postures (all species), (5) unilateral object removal from the mouth (gerbil), (6) bilateral thumb holding (squirrels), and (7) simultaneous holding/manipulation of two objects (squirrels). Only the guinea pig did not handle food with its paws, suggesting its behavior is regressive. The existence of a core pattern of paw and digit use in rodents suggests that skilled limb and paw movements originate at least with the common ancestors of the rod ent, and likely the common ancestor to rodent and primate lineages, wh ile species-typical movements suggest specialization/regression of lim b use has occurred in a number of mammalian orders. (C) 1998 Elsevier Science B.V. All rights reserved.