The Sexual Dimorphism Of Tianzhenosaurus Youngi

Ankylosaurs are considered as a monophyletic group of quadruped,plant-eating dinosaurs and a sister group of stegosaurs.They are characterized by a unique skull,a few longitudinal rows of bony plates on the back and both lateral sides of their bodies and small bergamot-like teeth.Ankylosaurs have been found from the continents of the Earth except Africa,and their stratigraphical distribution ranges from the Kimmeridgian Stage(Upper Jurassic)to the Maastrichtian Stage(Upper Cretaceous).Traditionally,ankylosaurs can be divided into two families of Ankylosauridae and Nodosauridae.This paper deals with four complete skeletons of Tianzhenosaurus youngi(Ankylosauridae)collected by Earth Science Museum of Hebei GEO University and Datong Museum of Shanxi Province.On the basis of anatomical(osteological)study,the sexual dimorphism can be recognized in Tianzhenosaurus youngi.The present paper is the first study on the sexual dimorphism of ankylosaurs and puts forward a new way for the study of ankylosaurs,in order to avoid the synonyms in classificantion.The preliminary results are given as follows:First,this paper describes the four skeletons of Tianzhenosaurus youngi(Ankylosauridae)collected from Earth Science Museum of Hebei GEO University and Datong Museum of Shanxi Province in detail and makes a comparative anatomical study.It turns out that Tianzhenosaurus youngi obviously shows a sexual dimorphism.The male individual has a thick and protruding squamosal horn and a large tail club,but the female has a relatively small squamosal horn and a very small tail club.Second,the emergence of sexual dimorphism further shows that Tianzhenosaurus youngi lived together in group,and the male individuals were responsible for definding foreign enemies and protecting family members.Third,this paper makes an osteological comparison of the left humerus between Tianzhenosaurus youngi and some related genera.Tianzhenosaurus youngi is similar to Saichania chulsanensis in the outline of left humerus,but the former does not develop an obviously large medial process of the left humerus.Tianzhenosaurus differs from Pinacosaurus and Talarurus in the outlines of left humerus and the characters of radius condyle.Fourth,this paper describes the first neck ring and the tail-handle of Tianzhenosaurus youngi for the first time.The first neck ring of Tianzhenosaurus youngi is clearly different from that of Saichania chulsanensis in the bony processes on the surface of the band(cervical half ring).The bony processes of the band in Tianzhenosaurus youngi are curved in shape,but the bony processes in Saichania chulsanensis are sharp in shape.Thus,we can distinguish Tianzhenosaurus youngi from Saichania chulsanensis based on the bony processes on the band.This provides new evidence for the difference between Tianzhenosaurus and Saichania.Lastly,the present paper also deals with the scattered bony plates of Tianzhenosaurus youngi,which can be roughly divided into 7 types according to their size,morphology and position on the body.Here we give an ecological restoration of Tianzhenosaurus youngi for the first time.