A toothed turtle from the Late Jurassic of China and the global biogeographic history of turtles

Abstract

BackgroundTurtles (Testudinata) are a successful lineage of vertebrates with about 350 extant species that inhabit all major oceans and landmasses with tropical to temperate climates. The rich fossil record of turtles documents the adaptation of various sub-lineages to a broad range of habitat preferences, but a synthetic biogeographic model is still lacking for the group.ResultsWe herein describe a new species of fossil turtle from the Late Jurassic of Xinjiang, China, Sichuanchelys palatodentata sp. nov., that is highly unusual by plesiomorphically exhibiting palatal teeth. Phylogenetic analysis places the Late Jurassic Sichuanchelys palatodentata in a clade with the Late Cretaceous Mongolochelys efremovi outside crown group Testudines thereby establishing the prolonged presence of a previously unrecognized clade of turtles in Asia, herein named Sichuanchelyidae. In contrast to previous hypotheses, M. efremovi and Kallokibotion bajazidi are not found within Meiolaniformes, a clade that is here reinterpreted as being restricted to Gondwana.ConclusionsA revision of the global distribution of fossil and recent turtle reveals that the three primary lineages of derived, aquatic turtles, including the crown, Paracryptodira, Pan-Pleurodira, and Pan-Cryptodira can be traced back to the Middle Jurassic of Euramerica, Gondwana, and Asia, respectively, which resulted from the primary break up of Pangaea at that time. The two primary lineages of Pleurodira, Pan-Pelomedusoides and Pan-Chelidae, can similarly be traced back to the Cretaceous of northern and southern Gondwana, respectively, which were separated from one another by a large desert zone during that time. The primary divergence of crown turtles was therefore driven by vicariance to the primary freshwater aquatic habitat of these lineages. The temporally persistent lineages of basal turtles, Helochelydridae, Meiolaniformes, Sichuanchelyidae, can similarly be traced back to the Late Mesozoic of Euramerica, southern Gondwana, and Asia. Given the ambiguous phylogenetic relationships of these three lineages, it is unclear if their diversification was driven by vicariance as well, or if they display a vicariance-like pattern. The clean, primary signal apparent among early turtles is secondarily obliterated throughout the Late Cretaceous to Recent by extensive dispersal of continental turtles and by multiple invasions of marine habitats.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0762-5) contains supplementary material, which is available to authorized users.

Ancient tropical extinctions contributed to the latitudinal diversity gradient

“…In addition, by using phylogenetic-based biogeographic models informed by fossils, we inferred that all groups had a widespread ancestral distribution that subsequently contracted toward the equator during Cenozoic cooling. This result is in agreement with previous fossil investigations for turtles 24,25,66 and crocodiles 23,44 . Range contraction in our study results from higher levels of range extirpations (i.e.…”

“…11). Our biogeographic estimates based exclusively on extant data conflict with the fossil record 23,24,66 . We overcame this bias by introducing information about the distribution of fossils into DEC, in the form of hard (HFC) and soft (SFC) geographic fossil constraints at specific nodes (see Methods; Supplementary Tables 7-9).…”

Slow and steady: the evolution of cranial disparity in fossil and recent turtles

“…As the principal mechanism, we suggest habitat loss resulting from the global drying that accompanied global cooling [90]. A second aspect that may have played an important role, however, is the increasing homogenization of global turtle faunas through the partial or full replacement of aboriginal turtle faunas on formerly isolated continent by modern cryptodiran faunas [83]. This process, once again, is most drastically illustrated in North America, where a fully indigenous turtle fauna consisting of helochelydrids and paracryptodires is fully replaced by cryptodires by the Palaeocene through the extinction of at least five paracryptodiran lineages filling unique portions of morphospace [34,35,84,85,88].…”

Sensory Evolution and Ecology of Early Turtles Revealed by Digital Endocranial Reconstructions

“…Even though more taxa have been assigned to the turtle stemlineage recently (Li et al, 2008;Lyson et al, 2010;Schoch and Sues, 2015), Proganochelys quenstedti remains one of the most important stem-turtles, given its phylogenetic position as the earliest shelled turtle with a completely preserved skull (Parsons, 1959(Parsons, , 1970Halpern, 1992;Joyce et al, 2016). Its endocast is a relatively simple structure when compared to that of crownturtles Mautner et al, 2017;PaulinaCarabajal et al, 2017;Ferreira et al, 2018).…”