In 1876, Zapsalis was first recognized based on the description of some teeth. However, beyond this dental evidence, our knowledge about Zapsalis remains quite limited. This is why the genus is often categorized as dubious, as attributing actual bones or fossils to it would be extremely challenging, mainly due to the limitations associated with tooth-based taxonomy.

Zapsalis was initially identified from teeth discovered in the Dinosaur Park Formation in Canada. Additional teeth were attributed to this genus from the Judith River Formation in Montana, USA. Nevertheless, many teeth from various fossil-rich formations have come into question, as they exhibit superficial dromaeosaurid characteristics without any distinctive or unique features.

The type tooth of Zapsalis, known as Z. abradens, is noteworthy for being flat on the lingual side, lacking mesial serrations, and possessing three distal serrations per millimeter. This tooth measures a total length of 12 millimeters.