A full sized adult Drepanosaurus had a length of about half a meter. Its name means "scythe lizard", which is thought to refer either to the enlarged claw on its forelimb, or the claw-like structure at the tip of its prehensile tail. The structure at the end of the tail is made of fused vertebrae.
The forelimb of Drepanosaurus is highly modified compared to other vertebrates and very robust. Its ulna was altered from being a forearm bone into an odd crescent shaped site for muscle attachment. The role played by the ulna in most tetrapods is replaced by an elongated carpal bone. Additional musculature would be attached to the high withers that characterized Drepanosaurus and its close relatives.
A clue to the purpose of these large muscles can be found on its hand. The animal's "index finger" bore a large claw reminiscent of those born by dinosaurs such as Noasaurus and Baryonyx. However it is more likely that Drepanosaurus used its claw like the modern pygmy anteater, tearing through bark and insect nests to find invertebrate prey. Some researchers have forwarded the more far-fetched proposal that the claw was used to excavate burrows, but this is unlikely.