Megalancosaurus is a genus of extinct reptile from the Late Triassic Dolomia di Forni Formation and Zorzino Limestone of northern Italy, and one of the best known drepanosaurids.

The type species is M. preonensis; a translation of the animal's scientific name would be "long armed reptile from the Preone Valley.

It was built like a chameleon and probably lived a similar arboreal lifestyle, feeding on insects and other small animals.

The tail is long, prehensile, and bears a strange claw-like organ made of fused vertebrae at its end.

Because not all members of the species appear to bear this digit, it has been speculated that it is an instance of sexual dimorphism, only being possessed by whichever sex needed a stronger grip on the branch during copulation.