Shape variation in presacral vertebrae of saltasaurine titanosaurs (Dinosauria, Sauropoda)

Abstract

Titanosaurs were small- to giant-sized sauropods, highly derived and highly pneumatic. Using morphometric analyses, we studied differences in shape of the presacral vertebral centra in some of these sauropods, especially in saltasaurines, and compared asymmetry patterns in lateral pneumatic foramina (LPF) between these titanosaurs and avian and non-avian theropods. Geometric morphometric analyses showed that the cervical centra tend to be elongated and dorsoventrally short, with an elliptical LPF located in the middle of the centrum; dorsal centra tend to be short and higher than the cervical centra, with the LPF slightly displaced to the anterior region. Shape variation can be described as a result of the ordering of the vertebrae within both the cervical and dorsal sequences, and therefore these methods can be applied to predict the position of isolated vertebrae. A persistent pattern of asymmetry among LPF was observed when length–height indexes were plotted. The right LPF are usually larger than those on the left side in the cervical vertebrae (except in Saltasaurus loricatus) but variable in the dorsal vertebrae. We propose an explanation of this asymmetry based on the asymmetric arrangement of viscera and late development of the respiratory (and air sacs) system.

Keywords::

• asymmetry
• geometric morphometrics
• pneumaticity
• presacral vertebrae
• Titanosauria

Acknowledgements

We thank Marcelo Reguero (MLP-Pv), Carlos Muñoz (MPCA-Pv), Jaime Powell (PVL), Alejandro Kramarz (MACN-Pv), Pablo Tubaro (MACN-OR) and Mariana Picasso (MLP-OR-Anexus) for allowing us the access to materials under their care. We thank Yolanda Davies (MACN-OR), Cecilia Kopouchian (MACN-OR), Claudia Tambussi (MLP-OR-Anexus), Ignacio Cerda (MCS) and Stella Maris Alvarez (MACN-Pv) for their assistance with the materials. Federico Gianechini and Mariela Fernández collaborated with technical details. We are grateful to Fernando Archuby, Laura Ventura and Jenny Fuentealba for their advice in statistical issues. We are grateful to Alejandro Otero and one anonymous reviewer for comments that substantially improved this article and to Phil Mannion for the timely and useful suggestions and for reviewing the English style.