Spondylosoma absconditum

von Huene 1942

Evidence: skeletal fragments.

Ladinian

Santa Maria Formation

Rio Grande do Sul; Brazil

Biology: 1.7 meters long – 2 kilograms

A much larger but possibly related dinosaur, Herrerasaurus, has been found with bite wounds from intraspecific antagonism. It is possible that all herrerasaurids led violent lives, but smaller individuals, such as Chindesaurus and Spondylosoma, may have led relatively quiet family lives. Perhaps it was a scrappy, little relative of Herrerasaurus that superficially resembled smaller herrerasaurids like Chindesaurus.

Evolution

Spondylosoma is composed of incomplete remains that cannot be associated with any other dinosaur families definitively and some of the bones assigned to this species may not belong to it (Langer 2007). Opinions as to the identity of Spondylosoma vary greatly. Most researchers agree that the dinosaurian status of Spondylosoma is doubtful at best (Langer et al. 2007 and Langer et al. 2010). Others have attempted to find affinities with other groups. Galton (2000) believed that the shape and position of the ribs indicated rauisuchian affinities but these were later shown to be more characteristic of Herrerasaurus, not rauisuchians (Langer 2007). Along with two small, compressed, serrated teeth, it has been considered a prosauropod (Kellner 1996) but, again, the assignment was unwarranted. There are certainly features that are shared with many basal dinosaurs, however, especially certain saurischians (Kellner et Campos 2000 and Langer 2007). Langer (2007) noticed similarities in the vertebrae between this species and the herrerasaurids Chindesaurus and Staurikosaurus, but also noted that the deltopectoral crests (projections of the bone at the shoulder) are short like those of the controversial genus Saltopus. The only viable options for placement at present seem to be the Herrerasauridae or, possibly, the Guaibasauridae, a position I have held previously. At present, I tentatively place this dinosaur in the Herrerasauridae, most similar to Herrerasaurus but possessing certain non-dinosaurian characteristics.

References:

Galton, P.M. 2000. “Are Spondylosoma and Staurikosaurus (Santa Maria Formation, Middle-Upper Triassic, Brazil) the oldest saurischian dinosaurs?” Paläontologische Zeitschrift 74(3): 393-423.

Kellner, A.W.A. 1996. “Remarks on Brazilian dinosaurs.” Memoirs of the Queensland Museum 39(3): 611-626.

Kellner, A.W.A., et D.A. Campos. 2000. “A brief review of dinosaur studies and perspectives in Brazil.” Anais da Academia Brasileira de Ciências 72(4): 509-538.

Langer, M. C. 2007. “Basal Saurischia.” In D. B. Weishampel, P. Dodson, et H. Osmólska (eds). The Dinosauria: Second Edition. Berkley, CA: University of California Press. 25-46.

Langer, M.C., M.D. Ezcurra, J.S. Bittencourt, and F.E. Novas. 2010. “The origin and early evolution of dinosaurs.” Biological Reviews 85(1): 55-110.

Langer, M.C., A.M. Ribeiro, C.L. Schultz, and J. Ferigolo. 2007. “The continental tetrapod-bearing Triassic of South Brazil.” In: Lucas, S.G., and J.A. Spielmann. The Global Triassic. New Mexico Museum of Natural History and Science Bulletin 41: 201-218.