How skilled are the skilled limb movements of the raccoon ( Procyon lotor)?

Abstract

Raccoons have been widely used for neurobiological research and with respect to paw (hand) use have been `considered' to be primates because they display highly developed skilled hand use. Their exceptional manipulatory ability is puzzling from an evolutionary perspective both because they belong to a taxon that is divergent from primates and because most members of their taxon are not especially skilled. Surprisingly, there has been no systematic investigation of their manipulatory ability. This was the purpose of the present study. Captive and zoo-housed raccoons were video recorded during food handling in a wide variety of conditions and the video records were subjected to descriptive frame-by-frame analysis aided by the use of Eshkol–Wachman Movement Notation (EWMN). The results confirm that raccoons display good manual skills in food finding, grasping and handling. Like primates, they use vision to identify and reach for objects, but additionally they make extensive use of haptically controlled movements. Unlike primates, they do not have a true convergent hand as it has limited flexive properties. Objects are grasped between the digits or between the apical digit and distal palmar pads. Manipulation of objects consisted of rolling the object between the palms of both hands, with little or no digit movement. Finally, although they can make unimanual reaching movements, they make extensive use of a bimanual reaching strategy. These results suggest that raccoons are like primates in that they display visual guidance of reaching, but are similar to other carnivores in that they do not use convergent grasping and digit manipulation and frequently use bimanual grasping. The results, consistent with a growing body of information on skilled use in mammals, including marsupials and rodents, suggest that raccoons are specialised, but not special.