辽宁下白垩统九佛堂组伊克昭龙一新种

伊克昭龙 (Ikechosaurus)是一类长吻的离龙类 ,以前根据内蒙古的材料建立了孙氏种 (I.sunailinaeSigogneau Russell,1 981 )及高氏种 (I.gaoiL櫣ｅｔａｌ.,1 999)。根据蒙古的材料建立的TchoiriamagnusEfimov ,1 979也于 1 983年被原作者归入本属。本文记述了辽宁义县皮家沟九佛堂组新发现的一个近于完整保存的骨架 (中国科学院古脊椎动物与古人类研究所标本编号 :IVPPV 1 32 83) ,并建立一新种 :皮家沟伊克昭龙 (Ikechosauruspijiagouensissp .nov .)。新种以下列特征区别于伊克昭龙其他种 :轭骨前伸约至泪骨之半 ;眶间距小于眼眶短径 ;眶后骨与后额骨不愈合 ;髂骨片前突不发育 ,颈区不收缩 ;四肢中桡胫骨与肱股骨之比相对较小。另外其荐前椎数目与孙氏种相同 ,为 2 5枚 ,比鳄龙属 (Champsosaurus)少 1枚 ;坐骨明显比孙氏种短 ;桡肱骨长度之比为 0 .5 8,胫股骨长度之比为 0 .60 ,在所知新离龙类 (Neochoristodera)中属最小 ;前肢腕骨至少 7块 ,后肢跗骨至少 6块 ;指 /趾式均为 2 3 4 4 3。在正型标本中其第二远侧跗骨在左右脚中不对称。提出眶后骨与后额骨的愈合与分离以及轭骨眶后支发育程度不能作为Simoedosaridae和鳄龙科间的鉴别特征 ;股骨内转子与股骨头分离不该作为高氏种的鉴定特征 ;新离龙类?

A NEARLY COMPLETE SKELETON OF IKECHOSAURUS PIJIAGOUENSIS SP.NOV.(REPTILIA:CHORISTODERA) FROM THE JIUFOTANG FORMATION (LOWER CRETACEOUS) OF LIAONING,CHINA

A nearly complete skeleton of a choristodere is described and Ikechosaurus pijiagouensis sp. nov. is erected on the basis of this specimen. This new species is distinguished from other species of the genus Ikechosaurus by the following features: the jugal extends anteriorly to about the middle of the lacrymal; the interorbital bar is narrower than the diameter of the orbit; the postorbital separated from the postfrontal; the anterior process of the iliac blade is less pronounced; there is no distinct neck region between the acetabulum and iliac blade; the ratio of epipodials to the propodials are relatively small. The morphology of this specimen reveals that certain characters like the fusion of the postfrontal and postorbital and the lack of a prominent postorbital process of the jugal cannot be used to diagnose the Simoedosaridae and Champsosauridae. Comparison with other choristoderes suggests that Ikechosaurus is more closely related to Tchoiria than with Champsosaurus and Simoedosaurus .