Morphometric Analysis of the Distal Epiphyses of the Radius and Ulna of Titanosaurs: A Case from Central India

Titanosaurs were one of the last surviving clades of sauropod dinosaurs, with a distribution that spanned the globe. India has an abundance of titanosaur fossil remains, but most of these bones are fragmented and incomplete. So far only a few radius and ulna bones of Indian titanosaurs are described, but only the ulna of Isisaurus colberti (ISIR 335/60) preserves the distal articular surface. Morphology of the distal epiphyses of the radius and ulna provides a few important characters for the phylogenetic analysis of sauropods. Here, we have described an ulna and a radius of two titanosaur specimens discovered in India. Earlier researchers have described variations in the distal articular shape for forelimb zeugopods and used them in the phylogenetic analysis of sauropods. Here, we conducted PC analyses to examine variations in the shape of the distal articular surface of radius and ulna among various taxa of eusauropods and compared them with the two specimens described here. The morphometric analysis identifies four major morphotypes in the ulnar distal articular surface shape and three major morphotypes in the radial distal articular surface shape. We also discuss evidence of homoplasy in these morphotypes among taxa from different clades of eusauropods analyzed in this study. The osteohistological study was conducted to examine bone tissue and the ontogenetic stage of these two Indian titanosaur specimens. The ulna described here belongs to a juvenile titanosaur, representing the first osteohistological description of a juvenile Indian titanosaur.