Cope was the first to describe a sail-backed synapsid with the naming of "Clepsydrops natalis" in his 1878 paper, although he called the sail a fin and compared it to the crests of the modern basilisk lizard ("Basilicus"). Sails were not preserved in the specimens of "D. incisivus" and "D. gigas" that Cope described in his 1878 paper, but elongated spines were present in the "D. rectiformis" specimen he described. Cope commented on the purpose of the sail in 1886, writing, "The utility is difficult to imagine. Unless the animal had aquatic habits, and swam on its back, the crest or fin must have been in the way of active movements... The limbs are not long enough nor the claws acute enough to demonstrate arboreal habits, as in the existing genus "Basilicus", where a similar crest exists."