The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida, Drepanosauromorpha)

Abstract

The pectoral girdle and forelimb of the Late Triassic drepanosauromorph reptile Megalancosaurus are redescribed and their function reinterpreted. The whole skeleton of this diapsid is highly specialised for arboreal life, and also the peculiarities of the shoulder girdle and forelimb were interpreted as adaptations for a limb-based locomotion using gap-bridging to move from one support to another, as in chameleons. Re-examination of the pectoral girdle and forelimb revealed the presence of clavicles fused into a furcula-like structure, a saddle-shaped glenoid and a tight connection between the radius and ulna that strengthened the forearm but hindered pronation and supination movements at that joint. The new information plus a reconstruction of the pectoral and forelimb musculature suggests that the forelimb was also specialised for grasping and raking in addition to climbing and thus prey capture may have been an important function for the forelimb. The new functional interpretation fits well with the overall body architecture of Megalancosaurus’ skeleton, suggesting that this reptile was an ambush predator that may have assumed a stable tripodal position, secured by the hooked tail and hind limbs, freeing its forelimbs to catch prey by sudden extension of the arm and firm grasping with the pincer-like digits.

Keywords:

• Megalancosaurus
• Diapsida Late Triassic
• pectoral girdle
• forelimb
• functional morphology
• palaeoecology

Acknowledgements

We wish to thank Cristina Lombardo, Curator of the Paleontological Collection of The Earth Sciences Department of Università degli Studi di Milano for permission to access to specimen MPUM 6008 and MPUM 8437 (Milano) Thanks are due also to Stefano Broccoli (Milano) for friendly support to the research and useful advices to one of the authors.

Disclosure statement

No potential conflict of interest was reported by the authors.