Reassessment of the phylogenetic interrelationships of basal turtles (Testudinata)

Abstract

Recent discoveries from the Late Triassic and Middle Jurassic have significantly improved the fossil record of early turtles. These new forms offer a unique opportunity to test the interrelationships of basal turtles. Nineteen fossil species are added to the taxon sample of the most comprehensive morphological phylogenetic analysis of the turtle clade. Among these additional species are recently discovered forms (e.g., Odontochelys semitestacea, Eileanchelys waldmani, Condorchelys antiqua), taxa generally omitted from previous analyses (e.g., chengyuchelyids, Sichuanchelys chowi) and species included in a phylogenetic analysis for the first time (Naomichelys speciosa and Siamochelys peninsularis). The coding of several characters is reassessed in light of recent observations, but also in order to reduce unwarranted assumptions on character and character state homologies. Additional characters from previous analyses, as well as five new ones, are also included, resulting in a data matrix of 178 characters scored for 86 turtle species and 7 fossil outgroups.The data set resolves the relationships of most newly included taxa, with the exception of Sichuanchelys chowi and 'Chengyuchelys' dashanpuensis. The phylogenetic placement of Heckerochelys romani, Condorchelys antiqua and Eileanchelys waldmani as stem turtles more derived than Kayentachelys aprix but more basal than Meiolania platyceps and Mongolochelys efremovi is corroborated. The relationships of chengyuchelyids remain unclear and more investigation is needed regarding these forms, yet interestingly they are unstable with respect to stem turtles. In contrast to previous analyses, Arundelemys dardeni is placed within pleurosternids. Siamochelys peninsularis falls within xinjiangchelyids. Perhaps the most salient conclusion of the present study is the placement of Naomichelys speciosa as a basal member of a clade uniting meiolaniids, Mongolochelys efremovi and Otwayemys cunicularius. This clade of rather large stem turtles was spread worldwide during the Mesozoic at least and persisted up until the Pleistocene with meiolaniids.This work is licensed under the Creative Commons Attribution 4.0 International License.CC-BY 4.0

A Review of the Fossil Record of Turtles of the CladePan-Chelydridae

“…This resulting "superfamilial" clade is named Chelydroidea following Baur (1893), who was the first to recognize this exact arrangement (Knauss et al 2011). Although current morphological studies still fail to retrieve a monophyletic Chelydroidea (e.g., Joyce 2007;Anquetin 2012;Sterli et al 2013;Rabi et al 2014), some compelling character evidence is nevertheless available that supports the monophyly of this clade (Knauss et al 2011).…”

A review of the fossil record of turtles of the clade Thalassochelydia

“…Joyce (2007) included an expanded sample by scoring Plesiochelys etalloni, Portlandemys mcdowelli, Jurassichelon oleronensis (his "Thalassemys" moseri), and Solnhofia parsonsi as terminal taxa, but they were found in a paraphyletic arrangement. More recent global phylogenetic analyses of turtles continued to include these species as separate terminal taxa Parham 2006, 2008;Sterli 2010;Anquetin 2012;Rabi et al 2013;Sterli et al 2013;Zhou et al 2014;Zhou and Rabi 2015), but none found them to form a monophyletic group.…”

“…Jurassichelon oleronensis is based on a single specimen (PIMUZ A/III 514) from the Tithonian of the Isle of Oléron, France (Rieppel 1980). This specimen represents one of the few skull-shell associations known for thalassochelydians and is therefore regularly included into phylogenetic analyses (e.g., Gaffney and Meylan 1988;Joyce 2007;Sterli 2010;Anquetin 2012;Rabi et al 2013). Rieppel (1980) originally referred this specimen to Thalassemys moseri Bräm, 1965, but pointed out that this species was probably more closely related to Plesiochelys than to Thalassemys hugii.…”

A Review of the Fossil Record of Turtles of the CladePan-Kinosternoidea

“…The pioneering studies of Hutchison and Bramble (1981) and synthesized the basal framework of kinosternoid evolution through the fossil record, and later studies have been able to add little more. These studies formed the basis for later analyses, in particular Knauss et al (2011) and Bourque et al (2014) and also informed global studies of turtle relationships (e.g., Joyce 2007;Anquetin 2012;Joyce et al 2013;Sterli et al 2013;Rabi et al 2014). Iverson (1991) in parallel provided a detailed morphological analysis that attempts to resolve the phylogenetic relationship of all extant kinosternids at the species level.…”

“…Although numerous morphological characters exist that could unite this highly inclusive clade, named Chelydroidea following Baur (1893) , current morphological studies still fail to retrieve this clade (e.g., Joyce 2007;Anquetin 2012;Sterli et al 2013;Rabi et al 2014). Nevertheless, the fossil record is more consistent with the molecular arrangement in that all pantrionychian clades can be traced back to the Early Cretaceous of Asia, whereas all chelydroid clades only emerged during the Late Cretaceous of North America (Crawford et al 2015), and because early representatives of the chelydroid lineage are difficult to distinguish from one another.…”