Typically portrayed in popular culture as being ugly, opossums have several physical traits that make them unlike any other North American mammal.  First, they are the only marsupial inhabiting the United States and Canada.  Their indicative coloration of white heads with pink noses and gray bodies makes them easily identified, however, their most remarkable anatomy is their long, naked, prehensile tail.  Although their unusual tail sometimes gets them misidentified as huge rats, opossums are not related to rodents and use their muscular tail to grip branches when climbing trees.