Megalancosaurus preonensis (Calvazara, Muscio and Wild 1980) Late Triassic ~210mya, was originally considered a possible bird ancestor when only the anterior was known, but later discoveries disproved that notion. Megalancosaurus was derived from a sister to Vallesaurus and was a sister to Drepanosaurus.
Distinct from Vallesaurus, the skull of Megalancosaurus had a slightly elongated rostrum. The antorbital fenestra was reduced by expansion of the the nasal and lacrimal. The posterior jaw line descended. The frontals were raised in a slight dome. The narrow rostrum and broad cranium suggest good binocular vision. The skulls of Vallesaurus and Megalancosaurus were both under 3 cm in length.
The rest of Megalancosaurus was greatly lengthened and deepened. The cervicals were each elongated and provided with neural spines that leaned anteriorly. The first few dorsal vertebral spines are enormously raised and enlarged to form a notarium. The rest of the neural spines were nearly as tall. Those arising from caudal vertebrae were T-shaped in lateral view. The caudal chevrons were expanded ventrally and fenestrated. A more distinct hook is formed at the tail tip.
The humerus was lengthened. The ulna was bowed. Manual digits II-IV were all shorter and more robust such that unguals I-IV aligned.
The ilium leaned anteriorly creating a pseudo anterior process. The hind limb was longer. Pedal ungual I was truncated. All other unguals were large and trenchant. The penultimate phalanges on III-V were the shortest.
Renesto (2000) considered the manus to be prehensile in the manner of chameleons (i.e. digits I-III opposing digits IV-V), but evidence for this is equivocal. A standard reconstruction appears to work just as well. The distal phalanges may be fused but vestiges of their articulations are still visible. |
