Characteristics of the newborns of Keichousaurus hui. (Reptilia Sauropterygia) from Xingyi Fauna(Ladinian,Middle Triassic), Guizhou Province

In this paper, 12 specimens with embryos and 49 newborns of the Keichousaurus hui from the Xinyi fauna of the Ladinian, the Middle Triassic are observed and measured.The ratio relationships of specific traits of body length, length of the humerus, femur and orbital length of the adult individuals and newborns have been carried on the statistical analysis. The characteristics of adult, embryo and young individuals are demonstrated, and the morphological characteristics of newborn of the Keichousaurus hui are described for the first time. The skull, cervical vertebra, dorsal vertebra, sacral vertebra, caudal vertebra and limbs of newborns of the Keichousaurus hui are quantitatively described. Besides, more complete and accurate anatomical information is obtained. The new materials show that the average length of the skull is 8.56mm, the humerus is shorter than the femur, and the ratio of humerus/femur is 1∶1.09. The head is triangular, the snout is short and blunt, the orbit is large and round with a unique narrow superior temporal foramen. In addition, it is demonstrated that the fetal head of the Keichousaurus hui is firstly produced from the maternal birth canal. Meanwhile, the distance between snout and hip of the newborns keep stable with a range of 31.04~32.26mm. Furthermore the change of this value is not directly related to the maternal size. This study provides new materials for the research of reproductive mode, ontogeny, especially allallic growth of the Keichousaurus hui.