A new, nearly complete stem turtle from the Jurassic of South America with implications for turtle evolution

Abstract

Turtles have been known since the Upper Triassic (210 Myr old); however, fossils recording the first steps of turtle evolution are scarce and often fragmentary. As a consequence, one of the main questions is whether living turtles (Testudines) originated during the Late Triassic (210 Myr old) or during the Middle to Late Jurassic ( ca 160 Myr old). The discovery of the new fossil turtle, Condorchelys antiqua gen. et sp. nov., from the Middle to Upper Jurassic ( ca 160–146 Myr old) of South America (Patagonia, Argentina), presented here sheds new light on early turtle evolution. An updated cladistic analysis of turtles shows that C. antiqua and other fossil turtles are not crown turtles, but stem turtles. This cladistic analysis also shows that stem turtles were more diverse than previously thought, and that until the Middle to Upper Jurassic there were turtles without the modern jaw closure mechanism.

Shell bone histology of solemydid turtles (stem Testudines): palaeoecological implications

“…All this evidence further corroborates the hypothesis that, with the possible exception of the Chinese Odontochelys semitestacea (Li et al 2008) and some post-Early Jurassic froms (i.e. Eileanchelys waldmani Anquetin, Barrett, Jones, Moore-Fay and Evans, 2009 and Herckerochelys romani Sukhanov, 2006: Scheyer et al 2014; also Condorchelys antigua Sterli, 2008: Cerda et al 2015, the majority of stem turtles showed terrestrial habitat preference (e.g. Joyce and Gauthier 2004;Sterli et al 2007).…”

Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata)

“…In addition, numerous molecular studies have supported archosaurian affinities for turtles (for a complete list, see Rieppel 2008: 348). Sterli (2008) recently proposed a partial revision of the phylogenetic analysis of Joyce (2007) in which she used four non-chelonian outgroups (Sphenodon punctatus, Simosaurus gaillardoti, Anthodon serrarius and Owenetta kitchingorum). The present analysis follows this proposal and extends it to include representatives of all clades that have been proposed as the closest relatives of turtles.…”

“…However, the aim of this analysis is not to produce a better-resolved phylogeny than previous studies, but to obtain a more comprehensive view of the relationships among the most basal members of the turtle clade. Sterli (2008) also proposed a modified version of Joyce's (2007) data set and scored three of the 19 species added herein (Heckerochelys romani, Condorchelys antiqua and Indochelys spatulata). Results from this study are discussed where appropriate.…”

“…The last two decades have witnessed the discovery of few additional early turtles such as Palaeochersis talampayansis (Late Triassic, Argentina), Australochelys africanus (Early Jurassic, South Africa), and Kayentachelys aprix (Early Jurassic, USA), which allowed to complete in some ways the turtle phylogenetic tree. However, it is the past few years which have been most exciting for specialists with the discovery of Late Triassic turtles more primitive than Proganochelys quenstedti (Li et al 2008;Joyce et al 2009), as well as of several species from the Middle Jurassic (Sukhanov 2006;Sterli 2008;Anquetin et al 2009), a period from which the turtle fossil record is particularly sparse. These discoveries coincided with a major reappraisal of phylogenetic relationships within turtles by Joyce (2007).…”

“…Joyce (2007) excluded from his analysis several early turtles whose relationships were uncertain: e.g., Indochelys spatulata (Datta et al 2000), chengyuchelyids (e.g., Ye 1994;Danilov & Parham 2008), Siamochelys peninsularis (Tong et al 2002), and Otwayemys cunicularius (Gaffney et al 1998). Additionally, several new basal turtles have been described since Joyce (2007) was published: Heckerochelys romani (Sukhanov 2006), Condorchelys antiqua (Sterli 2008;Sterli & de la Fuente 2010), Odontochelys semitestacea (Li et al 2008) and Eileanchelys waldmani (Anquetin et al 2009;Anquetin in press). Here, a new cladistic analysis is presented in order to test the relationships of these recently described and previously omitted species.…”