摘要
近年 ,越来越多的化石证据表明 :过去长期被认为只有鸟类才有的 ,并作为鸟类区别于其他脊椎动物的一些重要特征 ,如羽毛、叉骨、胸骨、尾综骨、前肢可折叠于体侧、眼眶与下颞孔相连的头骨及耻骨向侧后伸展的骨盆等 ,却也在 1亿多年前的不少小型兽足类恐龙身上或多或少地存在。于是 ,越来越多的人们相信鸟类是从小型兽足类恐龙起源。但迄今发现的所有具鸟类特征的恐龙 ,在时间上却晚于或至多也只是接近目前公认的最早鸟类———晚侏罗世的始祖鸟 ,而原始鸟类双弓型头骨似乎在暗示 :鸟类可能起源于比恐龙更古老的初龙类。这些都对鸟类起源于恐龙的假说提出了质疑。就目前的化石记录而言 ,鸟类和兽足类恐龙系统演化关系密切是毋庸质疑的。但由于至今未找到在时间上足以演化出鸟类的更古老近裔恐龙 ,因此还不能说恐龙就是鸟类的祖先。它们可能只是与原始鸟类平行独立发展的姊妹群 。
More and more of fossil records show that peculiar characters of modern aves,such as feather,furcula,keeled sternum,pygostyle,ulnare.orbit connected with infratemporal fenestra and pubes oriented posteriorly et al.,could be observed at a number of diminutive theropods of dinosaurs in different degree more than 100Ma ago.So more and more of people believe dinosaurs to be the ancestors of aves.Undoubtedly,aves near theropods in phylogenesis very much.All reported avian-like dinosaurs,however,are past or at the longest approach of accepted earliest avian,Late Jurassic Archaeopteryx lithographica (about 150Ma ago).A diapsid Congfuciusornis dui skull,on the other hand,suggests that primitive aves come from rather archaic reptiles,archosaurids,than dinosaurs.Maybe primitive aves and diminutive theropods of dinosaurs are parallel sister groups and rooted in a common ancestor.
出处
《江苏地质》
2004年第2期82-89,i001,i002,F003,共11页
Jiangsu Geology
