The axial skeleton of Silesaurus opolensis

Abstract

ABSTRACT A recent find of an articulated skeleton of Silesaurus opolensis at its early Late Triassic type locality Krasiejów (Poland), with skull, neck, pectoral girdle, and thorax, supplemented by additional preparation of previously collected articulated specimens, enables complete restoration of the vertebral column and associated skeletal parts. Cervical ribs of Silesaurus, well preserved in their original disposition, are parallel to the neck and extend backward for a few vertebral lengths. There is a sudden change in their morphology behind the seventh vertebra, although otherwise the transition from the cervical to the dorsal vertebrae is very gradual. Parapophyses slowly migrate upward along the anterior margin of the centrum and leave the centrum at the sixth or seventh dorsal vertebra. Narrowing of the dorsal extremities of the neural spines of the fourth and neighboring vertebrae suggests the ability of this region of the vertebral column to bent upward. There is thus a disparity between the structural and functional neck-thorax transition. The presence of three sacrals firmly connected by their ribs with the ilia and the long tail of Silesaurus, providing a counterbalance to the weight of the body in front of the pelvis, suggests the ability for fast bipedal running. However, unusually long but gracile forelimbs of Silesaurus suggest that it represents a transition towards secondarily quadrupedal locomotion, characterizing most of the later herbivorous dinosaurs.