Reassessment of the vertebral laminae in some South American titanosaurian sauropods

ABSTRACT

The neural spines of the sauropod presacral vertebrae contain a series of osseous laminae of unquestionable phylogenetic significance. However, the lack of articulated presacral series has impeded identification of these structures in many taxa. Titanosaur sauropods present a pattern of neural laminae that is somewhat different from other groups, especially to diplodocids. Understanding these differences is important in order to score adequately characters related to vertebral anatomy, in phylogenetic analyses of the Sauropoda. Particularly, many titanosaurs present two spinodiapophyseal laminae in the posterior dorsal vertebrae. Additionally, these taxa show the apparent disappearing of the postzygodiapophyseal lamina in those vertebrae. Other titanosaurs have a single posterior dorsal spinodiapophyseal lamina, but this probably corresponds to one (probably the anterior) of the two spinodiapophyseal laminae of the posterior dorsals of the other titanosaurs.

ACKNOWLEDGMENTS

We thank R. Martínez, O. Giménez, L. C. B. Ribeiro, B. González Riga, O. Hevia, A. Kramarz, and R. Coria for allowing the access to the collections of their respective institutions. Prebiterio Pacheco made the illustrations. Financial support was provided by PIP 6455 and PICT 357 to L. S. Jeff Wilson and an anonymous reviewer made useful suggestions for improvement of the manuscript.