三列齿类爬行动物化石在新疆的发现

TRITYLODONT REPTILE FROM XINJIANG

本文报道的三列齿类化石是该类动物在我国西北地区之首次出现,与四川自贡所产大山铺恐龙动物群中的自贡似卞氏兽(Bienotheroides zigongensis)归同属同种,故认为五彩湾组可与下沙溪庙组相对比。新标本的发现在若干形态特征上补充了以往记述之不足。

In China,tritylodont fossils have been reported recently from Jurassic beds of Sichuan Province,of a later geological age than that of the Lufeng fauna from Yunnan(Young,1982; He and Cai,1984;Sun,1986).In the summer of 1984,when the Xinjiang Expedition of IVPP were excavating dinosaurs in the Junggar Basin,a number of tritylodont fossils were discovered. It came from the Wucaiwan Formation in the northeastern part of the basin,from a locality called Jiangjunmiao.The collection consists of three incomplete skulls and other skull bones, lower jaw fragments and a few postcranial bones. The generic attribution is not difficult to ascertain,it possesses all the features characteris- tic of Bienotheroides:the shortened snout;extremely downward extension of the jugal arch;the short,wide and flat basicranial region;largely reduced maxilla and the direct contact of pre- maxilla with lacrimal and palate respectively. The materials described here are exactly identical to a species of Bienotheroides,B.zigon- gensis,which has been erected upon a skull from Sichuan(Sun,1986).This species has a cusp formula of 2-3-3 on its upper cheek teeth,which is distinguished from the 2-2-2 of Bienothero- ides wanhsienensis.In addition,this study reveals several features of this species,such as the wide and open articular fossa of the articular bone,the long and sharp angular process of the dentary,and the anteriorly located coronoid bone on the lower jaw. What worth while to be mentioned is the appearance of two small bones separately preserv- ed at the posterior portion of this skull.They are considered as from two different individuals, because both of them represent the same side of the skull.It has a triangular head which consists of a spherical end,a robust round process and a flat flange.The body is a cylindrical rod with a flat and somewhat inclined surface.One of them is situated medial to the quadratojugal, where the quadrate should be(Fig.2).They are probably hyoid elements as in Kayentathe- rium(Sues,1986).A quadrate with a robust stapedial process is also reported here. In Sichuan,the type specimen of Bienotheroides zigongensis came from Lower Shaximiao Formation which yields the Shunosaurus dinosaur fauna,Bienotheroides wanhsienensis appeared in the Upper Shaximiao Formation with the Mamenchisaurus fauna.Bienotheroides zigongensis is morphologically more primitive than B.wanhsienensis and that is in accordance with its ear- lier age.As the same species is found both from Xinjiang and Sichuan,the Wucaiwan Forma- tion of Xinjiang is considered to be of the same age as the Lower Shaximiao Formation of Sichu- an based on tritylodont fossils.