Tuatara Relative Survived Through KT/K-Pg Extinction Into Paleogene in South America

The youngest South American rhynchocephalian, a survivor of the K/Pg extinction

Authors:

Apesteguía et al

Abstract:

Rhynchocephalian lepidosaurs, though once widespread worldwide, are represented today only by the tuatara (Sphenodon) of New Zealand. After their apparent early Cretaceous extinction in Laurasia, they survived in southern continents. In South America, they are represented by different lineages of Late Cretaceous eupropalinal forms until their disappearance by the Cretaceous/Palaeogene (K/Pg) boundary. We describe here the only unambiguous Palaeogene rhynchocephalian from South America; this new taxon is a younger species of the otherwise Late Cretaceous genus Kawasphenodon. Phylogenetic analysis confirms the allocation of the genus to the clade Opisthodontia. The new form from the Palaeogene of Central Patagonia is much smaller than Kawasphenodon expectatus from the Late Cretaceous of Northern Patagonia. The new species shows that at least one group of rhynchocephalians not related to the extant Sphenodon survived in South America beyond the K/Pg extinction event. Furthermore, it adds to other trans-K/Pg ectotherm tetrapod taxa, suggesting that the end-Cretaceous extinction affected Patagonia more benignly than the Laurasian landmasses.

Pietraroian Rhynchocephalians From Albian Cretaceous Italy are Jurassic Relicts

A new sphenodontian (Reptilia, Lepidosauria) from the Lower Cretaceous of Southern Italy and the phylogenetic affinities of the Pietraroia Plattenkalk rhynchocephalians

Authors:

Cau et al

Abstract:

The Pietraroia Plattenkalk (Albian, Lower Cretaceous) of Southern Italy is known for well-preserved fossil vertebrates, including the rhynchocephalian lepidosaur Derasmosaurus pietraroiae. A previously described Pietraroian rhynchocephalian differs from Derasmosaurus in vertebral, pelvic and foot morphology. A third Pietraroian rhynchocephalian is described for the first time. The new specimen is smaller and more gracile than the other Pietraroian rhynchocephalians, shows a broad unpaired parietal with a small foramen, and robust dorsal neural spines. Comparison with the ontogenetic series of Sphenodon suggests that small body size and relatively broad parietal in the new rhynchocephalian indicate immaturity, although the complete obliteration of the interparietal suture and the relatively small size of the parietal foramen may support an ontogenetically mature condition for that specimen. The morphology of the dorsal vertebrae excludes referral to Derasmosaurus. Phylogenetic analyses placed the second specimen among the basal branch of Opisthodontia, and the third specimen and Derasmosaurus among Sphenodontinae. The phylogenetic reconstruction supports the interpretation of the Pietraroian rhynchocephalians as late-surviving members of Jurassic lineages.

Sphenotitan leyesi: a new Herbivorous Sphenodontian From Norian (?) Triassic Argentina

A new sphenodontian (Lepidosauria: Rhynchocephalia) from the Late Triassic of Argentina and the early origin of the herbivore opisthodontians

Authors:

Martinez et al

Abstract:

Sphenodontians were a successful group of rhynchocephalian reptiles that dominated the fossil record of Lepidosauria during the Triassic and Jurassic. Although evidence of extinction is seen at the end of the Laurasian Early Cretaceous, they appeared to remain numerically abundant in South America until the end of the period. Most of the known Late Cretaceous record in South America is composed of opisthodontians, the herbivorous branch of Sphenodontia, whose oldest members were until recently reported to be from the Kimmeridgian–Tithonian (Late Jurassic). Here, we report a new sphenodontian, Sphenotitan leyesi gen. et sp. nov., collected from the Upper Triassic Quebrada del Barro Formation of northwestern Argentina. Phylogenetic analysis identifies Sphenotitan as a basal member of Opisthodontia, extending the known record of opisthodontians and the origin of herbivory in this group by 50 Myr.