四川自贡大山铺的龟化石

四川自贡大山铺富产中侏罗世的龟类。这批化石,除个别几件已有记述外,其余更多保存在自贡恐龙博物馆的标本均未报道。本文除对它们进行系统记述外,并综观我国迄今已知中侏罗世的龟类,建立一新科,成渝龟科(Chengyuchclyidae fam.nov.),解决了我国这一时期龟类长期未定的归科问题。

FOSSIL TURTLES FROM DASHANPU, ZIGONG, SICHUAN

In the turtle collection from Middle Jurassic of Dashanpu, Zigong, Sichuan, there are morehan twenty shells, among hich only several ones have been studied respectively by Yehf1982) and Fang(1987), the others are now described ystematically, tngether with knownspecies in the present note. So far, four species belonging to two genera of turtles om middle Jurassic have beenreported in China, they are Chengyuchelys baenodies, C. zigongen.sis and C. dashanpuensis of,,(huan, and Xinjiangchelys junggarensis of North Xinjiang. Unfortunately, for many yearsunderstanding of the familial stematics f Chengyuchelys has been incomplete, and that ofXiniiaregcheh}s remains to be determined. It is therefore a new family, hengyuchelyidae, re-I,csentin} an early evolutionary branch of turtles, here proposed for them, and the diagnosisof the family ay be summarized as follows. 1'aracryptodiran turtles chiefly of middle Jurassic. Size medium to rather large. Carapaceoval, external surface of shell lacking obviousornamentation. Eight neural plates present, mostf tbem hexagonal in form nd with short-sides in front. Only otie suprapygal plate seen inXiniian,gchelys, large and expanding posterioyly. Plastron horter than carapace at anteriorand posterior ends, but with a .rather wide bridge. Rear margin of plastron nearly round,not oncaved strongly forwards. Mesoplastron present, situated in abdominal or between pee-tonal and abdominal scutes, and meeting ts pair at middle line. In Chengyzrc/zelys, at leastthree inframarginal scutes present, and its anal scute invaded to ypoplastron in middle part,but those of Xinjiongchelys unknown. Diagnosis of buttresses and parts of endoskeleton onlyseen n injinr7,gchelys: axillary and inguinal buttresses extended more anteriorly and posteriorlybut less up-wards than usual; angle etween scapular body and precoracoid process larger than900; lateral process of pubis varying in size; pubic symphysis large nd trongly projected for-、、ands; ilium extended somewhat backwards as seen in some bcenids; humerus and femur scout,ess curved d compressed ventro-dorsally.