The simplest way to identify animal tracks as belonging to an opossum is to look for the presence of a large opposable thumb on each of the hind tracks. Opossums are the only animals outside primates in North America to have prominent opposable thumbs.
Opossums have five digits on each paw; the digits on the front paws splay out widely, while the hind digits are arranged more compactly, with the exception of the thumb. The thumb is spread out by more than 90 degrees from the rest of the digits. Hind tracks often overlap or nearly overlap fore tracks, but the presence of a thick, inward-facing thumb print is always indicative of a possum even if the rest of the track is unclear.