Vallesaurus pelvic girdle and posterior limbs


Vallesaurus pes

Vallesaurus shares with some Megalancosaurus specimens a modified and opposable first toe, but it morphology is different from that of the first toe of Megalancosaurus 

Some  hints about phylogeny

The main differences between Vallesaurus and other adequately known drepanosaurids may represent plesiomorphic character states, like the lack of opposable digits in the manus and of the hooked spine at the end of the tail. Of particular interest is the morphology of the ankle joint, with the tibia contacting the centrale, which other than reflecting the primitive condition for drepanosaurids, may be indicative of a close relationship between drepanosaurids and protorosaurs. Indeed, the contact between tibia and centrale is considered a synapomorphy of the latter clade (Benton & Allen 1997). In Drepanosaurus and Megalancosaurus the centrale is excluded from a contact with the tibia by an increase in size of the distal portion of the astragalus which in Drepanosaurus becomes eventually fused with the calcaneum. This trend which is apparently paralleled independently in lepidosaurs. If this interpretation is correct, Vallesaurus could be the most primitive drepanosaurid so far known, at least until better preserved specimens of Hypuronector become available.



Home  Research Triassic Reptiles