A basal sphenodontian (Lepidosauria) from the Jurassic of Patagonia: new insights on the phylogeny and biogeography of Gondwanan rhynchocephalians

Abstract

Herein we describe a new rhynchocephalian taxon from the Middle Jurassic of Patagonia, Argentina, representing the first Jurassic record of the group in South America. The new taxon, consisting of a complete dentary, is ascribed to Sphenodontia based on the presence of a deep and wide Meckelian groove, long posterior process, well-developed coronoid process, and acrodont teeth showing dental regionalization including successional, alternate hatchling, and additional series. This allocation is reinforced by a phylogenetic analysis that places the new taxon in a basal position within a clade of sphenodontians that excludes Diphydontosaurus and Planocephalosaurus. Additionally, the new taxon clusters within a Gondwanan clade with the Indian Godavarisaurus from the Jurassic Kota Formation, sharing the presence of recurved and relatively large posterior successional teeth that are ribbed and bear a peculiar anterolingual groove. This sister-group relationship is intriguing from a palaeobiogeographical viewpoint, as it suggests some degree of endemism during the initial stages of the breakup of Pangaea. We also discuss the ontogenetic stage of the new taxon and provide insights on the evolution of successional dentition in rhynchocephalians.

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

“…The analysis yielded 22 most parsimonious trees of 218 steps, in all of which K. peligrensis is placed as the sister taxon of K. expectatus (as shown in the strict consensus depicted in figure 2) mainly based on the shared presence of a posterior fossa on the additional teeth, which has been previously considered 'one of the most conspicuous autapomorphic traits of Kawasphenodon' [9]. In agreement with previous hypotheses [4,19], Kawasphenodon as a whole is related to opisthodontians, recovered in a polytomy with Opisthias and eilenodontines (figure 2). Opisthodontians, including Kawasphenodon, share the presence of additionals that are square to transversely rectangular in cross section and moderately to tightly packed in the jaw, moving in a pro-oral fashion.…”

New Data on the Clevosaurus (Sphenodontia: Clevosauridae) from the Upper Triassic of Southern Brazil

“…The symphyseal area is oval, almost vertical, having three portions: a dorsal semilunar gap, separated from an oval symphysis by a shallow Meckel’s groove, ventrally to which there is another smaller gap (as in Sphenodon ) that is just above a small symphyseal process. As seen in all Clevosaurus , the symphyseal spur sensu [2], is reduced and roudend. The Meckel’s groove runs from the symphyseal area until the posterior limit of the basis of the coronoid process.…”

“…Here, these characters and scores are reproduced in order to keep the original enumeration. Regarding the OTUs (Operational Taxonomic Units) the Early Triassic lepidosauromorph Sophineta cracoviensis [56] was used to root the analysis intead of the basal Diapsida Youngina capensis (Late Permian of South Africa) [2,4,57]. The Squamata, represented only by the polychrotid extant lizard Pristidactylus in the original analysis, also includes Eichstaettisarus [58] from the Late Jurassic of Germany and Early Cretaceous of Spain and Italy, and a probably basal Gekkonomorpha [59] from the Early Cretaceous of Mongolia.…”

“…These are mainly represented in the Late Cretaceous, with Cenomanian-Turonian eilenodontine opisthodontians and Late Campanian fragmentary remains most likely related to opisthodontians [5–9], in addition to the Late Campanian to Early Maastrichtian record of a partial tooth bearing maxilla that closely resembles those of modern Sphenodon [10]. More recently, Sphenocondor gracilis from the Middle Jurassic of Patagonia was described as the first South American basal rhynchocephalian [2] and the first South American Paleogene sphenodontian, Kawasphenodon peligrensis , was described for the early Paleocene of Patagonia [4]. For the early Mesozoic (Late Triassic) of South American, sphenodontian opisthodontians are known from northern Argentina [3] and clevosaurs from south Brazil [11,12].…”

Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution

“…Other studies have suggested that the CGD created a 'filter barrier', allowing some clades to develop global distributions, while others were restricted to southern Gondwana (Pol & Rauhut, 2012). Dinosaur groups that apparently display a mixture of virtually globally distributed clades and others limited to southern Gondwana during the Jurassic include: tetanuran theropods (with 'basal' forms south of the CGD, and derived megalosauroids widespread across north Africa and Europe [Rauhut & Lopez-Arbarello, 2009); 'basal' eusauropods (Remes et al, 2009); and heterodontosaurid ornithischians (Pol, Rauhut & Becerra, 2011) (see also Apesteguía, Gómez & Rougier [2012] for an example from the Rhynchocephalia). One problem with this view, however, is that the absence of members of the southern Gondwanan groups in regions north of the CGD (and vice versa) might merely result from sampling failure.…”