Turtle Fossils Of Sinemydidae From Early Cretaceous Jehol Biota In Western Liaoning,china

Turtles are well diverse in terrestrial,semi-aquatic,and aquatic habits.These ecological diversities are influent more or less in the shell morphology,limb proportion,and phalangeal count(e.g.Joyce and Gauthier,2004;Renous et al.,2008).The terrestrial turtles(e.g.Testudo)have relatively short hand and foot with reduced phalangeal count.In contrast,the highly-aquatic turtles appear to have long hand and foot,the extremity is present in marine turtles(chelonioids)and pig-snout turtles(carettochelyids)(Joyce and Gauthier,2004).And also,some turtles(e.g.trionychids)trend to increase the phalangeal number as the hyperphalangy.The hyperphalangy is frequently present in aquatic tetrapods,and its extremity is well known in cetaceans,ichthyosaurs,and plesiosaurs,to form a long flipper for a highly-speed swimming.Although the hyperphalangy is not present as the flipper,additional phalanges of the soft-shelled turtles actually enlarge the paddle that functional for the rapid turn in water.In contrast,the hyperphalangy is rarely known in other turtles,especially in fossil turtles.Fortunately,hyperphalangy and elongated manus turtles were also found in the early Cretaceous Jehol biota.In this study,we reported a new freshwater turtle in detail below,Jeholochelys lingyuanensis gen.et sp.nov.from the Early Cretaceous Jehol Biota of western Liaoning,China.Jeholochelys lingyuanensis has a low-domed shell,as in other Cretaceous sinemydid and macrobaenids,and diagnostic with an unusual combination of features: midline contact of prefrontals;supraoccipital crest longer than squamosal crest;oval carapace clearly longer than wide;nuchal emargination shallow;preneural absent;eight neurals;two suprapygals;pygal present;third costals with parallel anterior and posterior sides;cervical scale present;vertebral scales wider than long;first vertebral wider than nuchal and contact second marginal;pleural 4 wider than long;sulcus plications of marginal scales 6-11 well developed.The turtle differs from the sinemydids Sinemys spp.in having cervical scale,pygalthe type species Xiaochelys spp.in having oval shell longer than wide,costo-peripheral fontanelles fully closed in larger size;mid-vertebral 2-4 scales distinctly narrower than vertebrals 1 and 5;lateral plastral fenestrae present and large sized.In contrast,the phalangeal formulate of 2-3-3-3-4 for pes possibly implies that a hyperphalangy is present in the new species,more than the phalangeal formulate of 2-3-3-3-3 of the crown turtles.By observing,measuring and comparing the fossils of this new genus,a systematic study of the morphological features of the bone and its growth and development,individual differences and possible sexual dimorphism.Here,we reported a new turtle from the Early Cretaceous Jehol Biota with elongated manus,as the soft-shell turtles,possibly representing a similar highly aquatic habit.Interestingly,this condition is also present in other co-existing turtles,implying a convergence with the soft-shell turtles in ecological habits.This convergence in turtles is possibly adapted for the cold climates in the Early Cretaceous Jehol Biota(Amiot et al.,2011).Its manus is well elongated as nearly twice as the ulnar length,comparable to these in highly aquatic turtles,possibly implying a similar habit.The main features of the new spiece: cranium elongated;prefrontals contact medially;temporal process of the parietal reduced;crista supraoccipitalis stout;vertebral scales wider than long;vertebrals 2-4 scales narrower than vertebral 1 and 5;preneural absent;two suprapygals subequal;suprapygal 1-peripherals 11 contact;anterior and posterior sides of costals 2-3 parallel;peripheral 1-costal 1 contact;manus elongated,as nearly twice as the length of the ulna;having unseparated prefrontals.The discovery of the new type of tortoise in this paper means that homo plasyphylla,which is similar to the present species,has appeared in the early stage of differentiation.In addition,this finding further increases the Jehol Biota classification and classification of turtle species diversity.At the same time,this paper describes and compares the skeletal characteristics of adult and juvenile specimen found in the strata of Yixian formation in Yixian,western Liaoning Province,and reveals a different developmental model.Among them,adult fossils were studied in detail by Zhou.A new turtle skeleton collected from the Yixian Formation of western Liaoning shows several characters,such as a shell that is longer than wide,and second to fourth vertebral scutes that are long and narrow.These characteristics are clearly distinct from the co-existing Ordosemys liaoxiensis but match those reported by Endo & Shikama(1942)in the original description of Manchurochelys manchoukuoensis.The new fossil is therefore identified as M.manchoukuoensis.It is similar to M.manchoukuoensis in cranial and shell morphology,sharing features such as the postorbital isolated from the squamosal,a relatively elongated crista supraoccipitalis,and a smaller anterior suprapygal.In addition,the juvenile features,such as a nearly circular shell,open lateral fontanelles and wider vertebral scales,are shown for the first time in M.manchoukuoensis by this specimen.This specimen shows that the ontogeny of M.manchoukuoensis is more comparable to that of S.lens,than that of C.bohlini or O.liaoxiensis.As the two best preserved specimens,their studies have provided a new insight into the relationship between skeleton and phylogeny of Cryptochelidae.In this paper,the study on the diversity of the development patterns of the family Turcidae in China is still in its preliminary stage,but it shows the characteristics of high diversity,and it is expected that more fossils will be discovered in the future.