August 25 , 2016

by Davidow

In a paper describing the anatomy of the primitive Triassic sauropod Antetonitrus ingenipes, McPhee et al. (2014) define the clade Sauropodiformes as including all sauropodomorphs more closely related to Sauropoda than to Massospondylus or Plateosaurus, and they slightly retreat from the original systematic placement of Antetonitrus in Sauropoda by treating it as a sauropodiform close to, if not, part of Sauropoda. However, while McPhee et al. summarize the importance of Antetonitrus in highlighting the transition from the sturdy massospondylids and plateosaurids to the bulky and massive sauropods, the use of the definition of Sauropoda sensu Salgado et al. (1997) by the authors should be taken with a grain of salt.

With respect to the cladistic analysis of Sauropod by McPhee et al. (2014), exclusion of Antetonitrus and Lessemsaurus from Sauropoda would render the sauropod clade Gravisauria Allain and Aquesbi, 2008 synonymous with the definition of Sauropoda sensu Salgado et al. (1997). However, Otero and Pol (2013) treat Antetonitrus, Blikanasaurus, and Lessemsaurus as sauropods under the definition of Sauropoda articulated by Allain and Aquesbi (2008), so it makes sense to retain the sauropod classification of Antetonitrus to avoid creating tiresome phylogenetic clade names in future cladistic analyses of basal sauropods because the Early Jurassic sauropodiform Aardonyx is more primitive than the only other non-sauropod sauropodiform clade from southern Africa, Melanorosauridae.

Irrespective of definition of Sauropoda offered by either McPhee et al. (2014) or Allain and Aquesbi (2008), I have decided to straddle the fence and treat Antetonitrus as a true sauropod just for the sake of phylogenetic accuracy and robustness.

Allain, R. and Aquesbi, N., 2008. Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas 30(2): 345-424.

McPhee, B. W., Yates, A. M., Choiniere, J. N. and Abdala, F., 2014. The complete anatomy and phylogenetic relationships of Antetonitrus ingenipes (Sauropodiformes, Dinosauria): implications for the origins of Sauropoda. Zoological Journal of the Linnean Society, 171: 151–205. doi: 10.1111/zoj.12127

Otero, A.; Pol, D., 2013. Postcranial anatomy and phylogenetic relationships ofMussaurus patagonicus (Dinosauria, Sauropodomorpha). Journal of Vertebrate Paleontology 33 (5): 1138-1168. doi:10.1080/02724634.2013.769444