Guaibasauridae

Taxobox
name = Guaibasaurids
fossil_range = Late Triassic


image_width = 250px
image_caption = "Guaibasaurus" fossil skeleton.
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Saurischia
familia = Guaibasauridae
familia_authority = Bonaparte "et al.", 1999
subdivision_ranks = Genera
subdivision =
* "Agnosphitys"?
* "Guaibasaurus" (type)
* "Saturnalia"

Guaibasauridae is a family of primitive saurischian dinosaurs, known from fossil remains of late Triassic period formations in Brazil and Argentina.

The exact makeup and classification of the Guaibasauridae remains uncertain. The family was originally named by Jose Bonaparte and colleagues in 1999 to contain a single genus and species, "Guaibasaurus candelariensis".Bonaparte, J.F., Ferigolo, J., and Ribeiro, A.M. (1999). "A new early Late Triassic saurischian dinosaur from Rio Grandedo Sul State, Brazil." "Proceedings of the second Gondwanan Dinosaurs symposium." National Science Museum Monographs, Tokyo 15: p89–109.] When a second specimen of "Guaibasaurus" was described from better remains in 2007, it became easier to compare it to other enigmatic early saurischians, which are often difficult to classify because they combine characteristics of the two major saurischian groups, Theropoda and Sauropodomorpha. Bonaparte and colleagues, in light of the information gained from this second specimen, found that the genus "Saturnalia" (which is anatomically very similar to "Guaibasaurus") could also be assigned to the Guaibasauridae, though they did not conduct a phylogenetic analysis or define Guaibasauridae as a clade. The researchers also tentatively assigned the poorly understood genus "Agnosphitys" to this family.Bonaparte, J.F., Brea, G., Schultz, C.L., and Martinelli, A.G. (2007). "A new specimen of "Guaibasaurus candelariensis" (basal Saurischia) from the Late Triassic Caturrita Formation of southern Brazil." "Historical Biology", 19(1): 73-82.]

Bonaparte and colleagues (2007) found that guaibasaurids have more characteristics in common with theropods than they do with early sauropodomorphs (or "prosauropods"). Because of this, according to Bonaparte, they are most likely either a very basal group on the stem leading toward sauropodomorphs, or a group ancestral to both sauropodomorphs and theropods. Furthermore, the authors interpret this as evidence that the common ancestor of both saurischian lineages was more theropod-like than prosauropod-like.

References