Functional morphology and ontogeny of Keichousaurus hui (Reptilia, Sauropterygia)

Abstract

Keichousaurus hui Young, 1958, from the Middle Triassic of Guizhou, China, is a small sauropterygian reptile. It has a short snout and elongated temporal openings, resembling the European pachypleurosaurid Dactylosaurus. Unlike all other stem-group eosauropterygians, the parietal foramen is displaced anteriorly. The neck is long and flexible. The body is rigid and the bones pachyostotic. There are two or three sacral vertebrae. There is distinct sexual dimorphism, as in Alpine pachypleurosaurids. The broad ulna is autapomorphic for Keichousaurus. The growth of the humerus is highly positively allometric, reflecting the principal role of the forelimb in locomotion. The overall horizontal orientation of the pectoral girdle indicates that Keichousaurus was not a subaquatic flyer. Instead, a drag-based regime was used in locomotion