A juvenile Diamantinasaurus matildae (Dinosauria: Titanosauria) from the Upper Cretaceous Winton Formation of Queensland, Australia, with implications for sauropod ontogeny

Abstract

ABSTRACT Although sauropod dinosaur bones are the most abundant vertebrate fossils found in the Upper Cretaceous Winton Formation of northeast Australia, only subadult and adult specimens have been described to date. Herein, we describe the first juvenile sauropod from Australia, derived from the Winton Formation (Cenomanian–lower Turonian). The preserved material belongs to a single individual and is sufficiently diagnostic to classify as a juvenile Diamantinasaurus matildae—the third specimen to be referred to the species. It also enables the identification of a new local autapomorphy for Diamantinasaurus: a distinct tuberosity on the medial surface of the scapula, posterior to the junction of the acromion and the distal blade. Nevertheless, several morphological changes are observable between the juvenile and the two adult skeletons of Diamantinasaurus matildae. These include less well-defined or entirely absent muscle attachment sites on the juvenile bones relative to the heavily scarred and rugose adult specimens. Overlapping elements between the juvenile and the two adult skeletons indicate allometric changes for Diamantinasaurus matildae throughout ontogeny, with limb bones growing at a more rapid proportional rate than other skeletal elements. Finally, we review the global record of juvenile sauropod remains, demonstrating that the growth patterns of sauropods vary greatly between taxa. Although titanosaurs display a range of isometry and allometry in the growth of individual bones, it appears that allometric growth was the primary pattern for this group.