Claw-Tailed Sickle-Lizard

Drepanosaurus unguicaudatus

    Drepanosaurus unguicaudatus is an arboreal reptile much like its relative Megalancosaurus, but it carries out its adaptations to an even greater degree then its cousin.

    Like Megalancosaurus, D. unguicaudatus has a muscular hump and powerful tail that aid it in climbing trees.  However, unlike Megalancosaurus, which climbs with the aid of opposable hands and feet, D. unguicaudatus ascends tree trunks by dint of raw strength.  Its toes do not form the grasping talons of its cousin, but are armed with long, sharp talons that grip tough bark.

    However strange is the body of D. unguicaudatus, its arms are its most bizarre features.  The large bone in the forearm---the ulna---has, in D. unguicaudatus, been transformed into a broad crescent of bone and its function has been  replaced by the ulnare, a bone of the wrist (Peters).  This odd arrangement has altered the ulna's purpose from a structural support of the arm into an anchor for a great muscle that allows D. unguicaudatus to rest all of its substantial weight on the immense claws of its forelimbs.  The claws (located in the index finger) are used to grip the bark of the tree and D. unguicaudatus uses them to pull itself upward.  They are also useful prizing tools and, aided by D. unguicaudatus's narrow  beak, they can extricate small insects from the bark of trees.

    D. unguicaudatus's tail, the species' namesake, is tipped with a claw formed of fused vertebrae (Peters).  This adaptation makes the prehensile tail an even better grasping tool.

(Thanks to John V Jackson for his suggestion about the feeding habits of D. unguicaudatus)

Other sites containing pertinent information:

• Vertebrate Paleontology's Drepanosauruspage (with lots of information, but few pictures)