A New Specimen Of Sinemydidae From The Jehol Biota In Western Liaoning,China

In the Jehol Biota,most of turtle fossils belong to a primitive cryptodiran group,Sinemydidae,characteristic by having a low domed shell and a ligamentous connection between carapace and plastron.Up to date,four taxa have been named in the Jehol Biota,such as Manchurochelys manchoukuoensis Endo & Shikama 1942,Ordosemys liaoxiensis Ji 1995,Liaochelys jianchangensis Zhou 2010,Xiaochelys ningchengensis Zhou & Rabi 2015.A new turtle(PMOL-AR00222)from Early Cretaceous Jiufotang Formation of Sihedang Township,Lingyuan City,western Liaoning Province.It is characteristic by combined features: nasal absent;prefrontals contact one another along the midline;interorbital roof narrow;parietal separate from squamosal;suparoccipital ridge slightly longer than squamosal crest;low domed shell,longer than wide;two suprapygals are subequal;the pedal formula of 2-3-3-3-4.However,I referred it as a Sinemydidae gen.et sp.Indet.Because the new specimen is an juvenile and has deformity in vertebral scales.Additionally,hyperphalangy,known in several extant aquatic turtles(e.g.soft-shelled turtles),is also present in the new specimen as an aquatic adaption.Moreover,it shows a deformity of vertebral scales in having seven rather than five vertebral scales in formal pattern.Several possible coprolites are preserved without obvious bone or scales inside,implying a strong digestive ability as in extant turtles.Based on the well-preserved skeleton,this study firstly reports a deformity of vertebral scales and coprolites for the Sinemydid turtles,shedding a light on the development and ecology of the Mesozoic turtles.