A new species of Callawayia (Reptilia: Ichthyosauria) from the Late Triassic in Guanling, Guizhou

Abstract：Based on Shastasaurus neoscapularis, which was firstly described from the Late Triassic Norian of British Columbia, Canada by McGowan (1994), Callawayia and Comparison: The new species is similar to Callawayia neoscapularis in a contact between the nasal and postfrontal, well-developed parietal ridge and parietal shelf, contact between the postfrontal and supratemporal, relative slender scapular, and humerus with higher dorsal process, but it can be distinguished from the latter by a narrow frontal, nearly straight frontonasal suture, and a well-developed maxilla dorsal lamina.Metashastasaurus were successively established by Maisch and Matzke (2000) and Nicolls and Manabe (2001). Callawayia is used in this paper according to the ICZN, but its diagnosis is mainly based on that of Metashastasaurus given by Nicolls and Manabe（2001）because the their study was more detailed and correct.The present specimens were collected from micrite of the lower part of the Upper Triassic Xiaowa Formation. It is very important both in biostratigraphy and biogeography because it not only enlarged the geological and paleogeographical range of Callawayia, but also proved the successive evolution of the ichthyosaurs fauna from the Late Triassic Carnian to Norian.The genus Callawayia was usually assigned to Shastasauridae in the past; however, the plesiomorphic features of the skull and appendicular skeleton, which have been recognized from tplete specimens of Shastasaurus from the Upper Triassic Xiaowa Formation by the authors recently, indicate the distinctive difference between Shastasaurus and Callawayia. A formal revision of their systematic position would be worthy of efforts, but it is not the emphasis of this study. Because the humerus, which is broad, short and nearly quadrangular, shares characters of Infraorder Shastasauria Motani 1999, Callawayia is described based on the ichthyosaurs systematic classification proposed by McGowan and Motani（2003）in this paper. Superorder Ichthyopterygia Owen 1840 Infraorder Shastasauria Motani 1999b Family incertae sedis Genus Callawayia Maisch and Matzke 2000 Callawayia wolonggangense sp. nov. Etymology：Wolonggang-, a hill, about 3 km north of Xinpu Town, Guanling, Guizhou Province. It is well-known where abundant and well-preserved marine reptiles and crinoids fossils were found.Holotype：Sample No. SPCV10306 of the Yichang Institute of Geology and Mineral Resources, a nearly complete articulated skeleton Paratype：Sample No. SPCV10305 of the Yichang Institute of Geology and Mineral Resources, a flatten skull.Typical locality and horizon: Xinpu Village, Guanling County, Guizhou Province; Xiaowa Formation, Canian, Upper Triassic.Diagnosis: Medium-sized ichthyosaur with along snout, which was almost covered by premaxilla; maxilla dorsal lamina contacting prefrontal; frontal separating from prefrontal by contact between nasal and postfrontal; narrow frontal entering supratemporal fenestra, and forming a trough anterior terrace of upper supratemporal fenestra; parietal ridge and posterior parietal shelf well-developed; postorbital and squamosal separating from supratemporal fenestra by contact between postfrontal and supratemporal; dorsal central being anterior concave; scapular shaft elongated; humerus being short and broad, with well-developed dorsal process; leading edge of flipper notched, front flipper with 4 digits.