Your Daily Fossil

Vallesaurus

When: Late Triassic (~210 million years ago)

Where: Italy 

What: Vallesaurus is the most complete drepanosaur (monkey lizard) ever found. This tiny lizard is only 6 inches (~16 cm) long, making it much smaller than most of its relatives. Like the rest of the clade it was an arboreal lizard, with not only long fingers and toes well adapted for gripping branches, but also a prehensile tail. Prehensile tails have developed several times in both reptiles and mammals, with chameleons an example of a  living prehensile lizard. In many ways Vallesaurus and its close relatives can be thought of as triassic chameleons, occupying the same tree-dwelling and insect -eating reptile niche. More derived drepanosaurs also have opposed fingers, as in chameleons, and evidence of the same mechanism that allows chameleons to quickly dart their head forwards to capture prey.  Little Vallesaurus itself does not have these adaptations, as it is a fairly primitive drepanasaur, and it is likely that it moved though the trees much faster than the rest of its clade and modern chameleons. Thus, it is shown that this group was already well adapted at climbing trees before converging upon a modern chameleon body plan. The vast majority (if not all) fossils of Vallesaurus and its kin are found in lake deposits, showing that these animals were at home high in the tree tops, with branches that reached out far over the waters. And that despite the large suite of climbing adaptations, they sometimes misstepped and took quite the plunge. 

Vallesaurus is not closely related to any living lizard. Its clade is yet another group of ancient reptiles that do not have a very well understood position in the tree of life. However, it is universally agreed that they are diapsid reptiles, and more closely related to archosaurs than to lizards. 

Reconstruction by Matt Celeskey at the  New Mexico Museum of Natural History & Science