Ancistronychus

Drepanosaurs were already some extremely weird animals, even among all the other weirdos of the Triassic period.

These strange little tree-climbing reptiles had chameleon-like bodies, humped backs, long necks, and oddly bird-like skulls with toothless beaks – and then some of them also had bizarre forelimb anatomy with a single enormous claw on the second finger of each hand, along with a claw on the tip of their prehensile tail.

But new discoveries are showing that some members of this bizarre group were doing something different.

Ancistronychus paradoxus here lived during the late Triassic, about 227 million years ago, in what is now the southwestern United States. Measuring around 50cm long (1’8″), its enormous hand claws were unusual compared to its close relatives, with a distinctly wide and hooked shovel-like shape.

Along with another recently-discovered species, Skybalonyx skapter, and the weird burly arms of Drepanosaurus, this suggests that instead of tree-climbing some drepanosaurs were instead much more specialized for digging. They may have been Triassic equivalents to modern anteaters or pangolins, using their enlarged claws to excavate burrows and rip their way into insect nests.

Drepanosaurus

One of my favorite palaeontological discoveries of 2016 also involved one of my favorite extinct animals: the odd little “monkey lizard” Drepanosaurus.

Living during the Late Triassic of Europe and North America (~218-212 mya), this reptile measured about 50cm long (20″). It was already known to have some particularly weird anatomy, featuring a humped back, grasping feet, a prehensile tail ending in vertebrae modified into a pseudo-claw, enormous claws on the second finger on each hand, and a bizarre arrangement of its forearm bones.

In 2016, new fossils gave us a better look at those arm bones, and they turned out to be even stranger than previously thought. As well as the radius and ulna being unusual, several wrist bones were also heavily modified and elongated, creating an arm setup unique among all known tetrapods. This may have been a specialization for “hook-and-pull” digging, ripping up tree bark to get at burrowing insects – but now the real mystery is why no other tetrapods have ever managed to modify their limb bones to this sort of extreme.