Preliminary phylogenetic and histological analysis of a Late Triassic sauropodomorph from the Lower Elliot Formation of Lesotho

EMIL KRUPANDAN ; ALEJANDRO OTERO; ANUSUYA CHINSAMY

Los Angeles

Congreso; 71° Annual Meeting of the Society of Vertebrate Paleontology; 2013

Society of Vertebrate Paleontology

One of the richest known Late Triassic ? Early Jurassic sauropodomorph faunal assemblagesis the Elliot Formation of South Africa. It is dominated by sauropodomorph dinosaur remains consisting of Antetonitrus ingenipes, Blikanasaurus cromptoni, Melanorosaurus readi,Massospondylus, Plateosaurus cullingworthi, Eucnemesaurus fortis and Aardonyx celestae. In the current study, we assessed the remains of undescribed sauropodomorph material that was excavated during the 1950?s from the Late Triassic, Lower Elliot Formation in Lesotho. The material is represented by at least 5 individuals of varying ontogenetic sizes, excludes crania, but comprising of more than 250 postcranial elements. Previous researchers suggested that the material belonged to either a ?prosauropod? similar to either Plateosaurus or Melanosaurus, or to Euskelosaurus browni (nomen dubium). In the current study, we performed a detailed character analysis to assess the taxonomic affinity of this dinosaur material. In addition we conducted histological studies of three femora to deduce aspects of its biology and growth dynamics. Our phylogenetic analysis recovers the postcranial material as a basal non-eusauropod sauropod, in a polytomy with Antetonitrus, Lessemsaurus, Gonxianosaurus and an as yet unnamed taxon from Argentina (PULR 136. Based on the sharing of three of the five apomorphies of Ante it appears that these remains represent multiple individuals of Antetonitrus or a very closely allied taxon. The femoral bone histology shows highly vascularised fibrolamellar bone tissue, suggesting rapid rates of bone deposition. Towards the outer 8% there appears to be a slowdown in the rate of bone formation with several lines of arrested growth evident. This growth pattern differs from that of basal sauropodomorphs and is generally consistent with that observed in sauropod. Our cladistics and histological findings suggest that the material from Lesotho represents a basal sauropod, possibly Antetonitrus or otherwise a close relative.