Chelonii: Eucryptodira: Xinjiangchelyidae and related forms

Taxa on This Page

1. Chengyuchelyidae X
2. Chengyuchelys X
3. Larachelus X
4. Xinjiangchelyid - Crown Cryptodire clade
5. Xinjiangchelyidae X

Descriptions

Xinjiangchelyid - Crown Cryptodire clade common ancestor of Xinjiangchelys latimarginalis and extant Cryptodira, and all its descendants

Range: Middle Jurassic to Recent

Characters: anal scutes anteromedially overlapping the hypoplastra. - Pérez-García & Murelaga (2012)

Comments: node D in Fig. 5A-B of Pérez-García & Murelaga (2012). This clade includes several Mid Jurassic to Early Cretaceous Asian and Early Cretaceous European taxa along with crown group Cryptodira. It represents a more advanced grade of organisation than the late Jurassic plesiochelyids and their relatives. As the Xinjiangchelyidae are almost certainly paraphyletic (Rabi et al 2010), this clade represents the Xinjiangchelyid grade of organisation and later forms. MAK130403

Chengyuchelys Ye 1990 : Chengyuchelys baenoides C. zigongensis

Range: Bathonian (Middle Jurassic) of China

Characters: Chengyuchelyidae Ye 1990 - oval carapaces lacking ornamentation, eight hexagonal neural plates, round posterior margin, mesoplastron, intergulars, and inframarginals (Lucas, 2001 p.138). Considered a definite clade by Anquetin, 2009 pp.193-4 on the basis of the following esoteria: vertebrals 2 to 4 as narrow as, or narrower than, pleurals; medial embayment of vertebral 3-4 sulcus present; dagger-shaped entoplastron present; and anal scales overlap anteromedially onto hypoplastra. Elsewhere synonymised with Xinjiangchelyidae (see notes)

Comments: Chengyuchelys retains mesoplastra, a very primitive feature. According to Anquetin, 2009 this is a stem clade, although the included taxa are rather unstable, jumping around a lot in the various cladograms (Anquetin, 2009 p.193). The Dashanpu locality is unusual in having at least four species of turtles, as all other turtle localities from this time have only one species each. With the earliest stratigraphic record from the Shaximiao formation of Sichuan, China (Bathonian or perhaps Bathonian-Callovian age), these are among the earliest of intermediate stem testudines, contemporary with Condorchelys and Eileanchelys. They represent either a very primitive group convergent with eucryptodires, or one of a number of diverse Jurassic eucryptodirian turtles. The phylogenetic placement of Chengyuchelys is very difficult to resolve (Anquetin, 2009). Anquetin, 2009 decided on a very basal placement, distinct from Xinjiangchelys. If so this would be an example of the co-existence of two highly endemic and similar clades of Jurassic Chinese tetrapods, one very primitive and the other more advanced, similar to that of the sauropod dinosaurs, of which two exceptionally long-necked Jurassic Chinese types are known, the primitive but successful mamenchisaurs and the more advanced euhelopines, although unlike the Jurassic turtles these two groups were not contemporary. However, Danilov & Parham, 2008, in a study of two poorly known specimens of Chengyuchelys baenoides from the Middle Jurassic of Dashanpu, Sichuan Province, China, found that this species came out as the sister taxon to Xinjiangchelys, which implies that the two families should be synonymised. Pérez-García et al (2013) include both Chengyuchelys and Xinjiangchelys in a monophyletic Xinjiangchelyidae, whilst Pérez-García & Murelaga (2012) recover both Chengyuchelys and Xinjiangchelys in an unresolved polytomy of advanced stem eucryptodires, the other taxa included there being Late Jurassic to Early Cretaceous. MAK130119.

Xinjiangchelyidae : Annemys, Brodiechelys, Siamochelys, Tienfuchelys, Yanduchelys, Xinjiangchelys.

Range: Middle and Late Jurassic of Asia, early Cretaceous of Asia and Europe

Characters: Dorsal carapace and the ventral plastron with a ligamentous connection rather than the usual solid bridge of bone (Danilov, 2005). distinctly sinuous midline sulcus of plastral scales and gular scales restricted to epiplastra (Anquetin, 2009 p.197)

Comments: Xinjiangchelyidae are medium-sized (carapace length up to 375 mm) aquatic turtles best known from the Middle and Upper Jurassic of Asia. These are the earliest known eucryptodires (predating the more primitive Plesiochelyid grade). Xinjiangchelys seems more advanced than the Late Jurassic plesiochelyids and Hylaeochelys in the possession of the extensive posterior temporal emargination, the procoelous and opisthocoelous caudals, and narrower vertebral scutes. (Hirayama et al 2000 p.189). If Brodiechelys brodiei (Lydekker, 1889) from the Early Cretaceous of England and Spain is closely related (Hirayama et al 2000, Pérez-García et al (2013)), it would indicate a wider geographic and stratigraphic distribution for the group. They are generally seen as the sister group to the Centrocryptodira of Gaffney, 1975 (Scheyer 2007 p.68) although this classification is not used in more recent cladograms (Joyce 2007, Anquetin, 2009). The contemporary Chengyuchelys is considered much more basal, as it retains mesoplastra, a primitive feature (Anquetin, 2009) although one study places it as the sister taxon to Xinjiangchelys (Danilov & Parham, 2008). Most workers consider Xinjiangchelyids to be more closely related to modern cryptodires than Paracryptodira or Plesiochelyidae (Gaffney 1996; Hirayama et al. 2000; Joyce 2007; Parham and Hutchison 2003) and (with the exception of Danilov and Parham (2008)), basal to the Sinemydidae-Macrobaenidae assemblage (Rabi et al 2010) However their monophyly has not been demonstrated, with the vast majority of characters that are used to diagnose this group being symplesiomorphies for eucryptodira when mapped onto global trees (Rabi et al 2010). "Xinjiangchelyidae" is therefore likely paraphyletic grade of early eucryptodires, similar to, but less advanced than, the "Sinemydidae" and "Macrobaenidae." MAK121126 130403

Links: Annemys sp., Fossil Cryptodire and Xinjiangchelys radiplicatoides, Fossil Cryptodire from Digimorph; Mikko's Phylogeny Archive (dendrogram)

Reconstruction of the shell of Larachelus morla, from Pérez-García & Murelaga (2012). A, posterodorsal, B, dorsal, and C, ventral views. Scale bar is 5 cm. The high domed shell may indicate a terrestrial liufestyle

Larachelus morla Pérez-García & Murelaga 2012

Horizon: Pinilla de los Moros Formation, late Hauterivian-early Barremian, Salas de los Infantes, Burgos, western Cameros Basin, Spain.

Characters: "partially ligamentous epiplastrahyoplastra and hypoplastra-xiphiplastra contacts, with a linear ridge in the anterior margin of the hyoplastra and posterior margin of the hypoplastra that slots into a furrow in the posterior margin of the epiplastra and anterior margin of the xiphiplastra, respectively. Differs from other pan-cryptodires by the following: high shell; broad plastral lobes; smooth outer surface; absence of fontanelles" -Pérez-García & Murelaga (2012)

Comments: One of a number of recently discovered or redescribed European Early Cretaceous pan-cryptodiran turtles, with similarities to Asian taxa like the Xinjiangchelyidae. It is clear that these animals were widespread and diverse, with several clades of turtles, including paracryptodires, stem cryptodires, and several lineages of the crown group Cryptodira. This wide range of morphological diversity can be related to adaptation to different ecological niches. Pérez-García & Murelaga (2012) MAK130403