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Abstract
The skull anatomy of Mussaurus patagonicus from the Upper Triassic Laguna Colorada Formation is described based on a revision of the type material and several recently found specimens. The studied material include two distinct size classes of individuals. The type material consists of extremely young individuals whereas the new specimens are interpreted as juvenile or subadult individuals. The latter are significantly larger, having a skull approximately three times longer than the type material. The skull anatomy of this taxon shows derived characters shared with some basal sauropodomorphs and eusauropods, which are absent in other basal sauropodomorphs (e.g. Thecodontosaurus, Plateosaurus). These include the presence of an extension of the infratemporal fenestra ventral to the orbit, dorsal and anterior rami of quadratojugal subperpendicular to each other, dorsoventral expansion of dentary at mandibular symphysis, slightly procumbent teeth with broad serrations restricted to the apical region (absent in some teeth). Differences among the studied specimens helps to understand the early ontogenetic changes occurring in this basal sauropodomorph, revealing major changes in the rostral and temporal regions.
Acknowledgements
We would like to thank Mark Norell, Jim Clark, and Paul Olsen for providing critical reading of earlier versions of this work. Discussions regarding these topics with J. Bonaparte, J. Wilson, P. Sereno, A. Yates, P. Upchurch, P. Barrett, and P. Galton are greatly appreciated. The PVL material was collected by Bonaparte et al. during a project developed with the financial support of the National Geographic Society. We would like to thank the Subecretaría de Cultura of Santa Cruz Province and the Museo Provincial Padre M.J. Molina for their collaboration and support on the field project conducted in El Tranquilo Group. We are thankful to P. Puerta, M. Cardenas, S. Reuil, D. Pais, A. Scanferla, A. Mancuso, M. Puerta, and A. Lecuona for their participation in the field season. Part of this project was developed with the financial support of the Division of Paleontology (AMNH), Theodore Roosevelt Fund, and the Annette Kade Fund (to D.P.). Preparation of the specimens MPM was executed by P. Puerta, M. Caffa, L. Canesa, and J.L. Carballido. J. Gonzalez conducted the line drawings of Figures and . Comparisons with relevant material was possible thanks to the collection access provided by: J. Bonaparte (MACN), M. Norell (AMNH), X. Xing (IVPP), A. Kellner and L. Leal (MNRJ), R. Wild (SMNS), S. Kaal (SAM), J. Gauthier (YPM), D. Unwin (HMN), M. Feng (JMG), M. Langer (USP), M. Palacios (MPM), B. Rubidge and A. Yates (BPI), R. Nuttal and E. Butler (NMQR), and F. Knoll (MNHN).