Scanlon John D
Riversleigh Fossil Centre, Outback at Isa, PO Box 1094, Mount Isa, Queensland 4825, Australia.
Nature. 2006 Feb 16;439(7078):839-42. doi: 10.1038/nature04137.
Understanding the origin and early evolution of snakes from lizards depends on accurate morphological knowledge of the skull in basal lineages, but fossil specimens of archaic snakes have been rare, and either fragmentary or difficult to study as a result of compression by enclosing sediments. A number of Cenozoic fossil snakes from Australia have vertebral morphology diagnostic of an extinct group, Madtsoiidae, that was widespread in Gondwana from mid-Cretaceous (Cenomanian) to Eocene times, and also reached Europe in the late Cretaceous period. Despite this long history, only about half the skull is known from the best-known species Wonambi naracoortensis, and the few known cranial elements of other species have added little further evidence for phylogenetic relationships. Conflicting hypotheses have been proposed for their relationships and evolutionary significance, either as basal ophidians with many ancestral (varanoid- or mosasaur-like) features, or advanced (macrostomatan) alethinophidians of little relevance to snake origins. Here I report two partial skeletons referred to Yurlunggur, from the late Oligocene and early Miocene of northern Australia, which together represent almost the complete skull and mandible. The exceptionally preserved skulls provide new evidence linking Yurlunggur with Wonambi and other madtsoiids, falsifying predictions of the macrostomatan hypothesis, and supporting the exclusion of Madtsoiidae from the clade including all extant snakes.
了解蛇类从蜥蜴演化而来的起源和早期进化，依赖于对基干谱系中头骨的准确形态学认识，但古老蛇类的化石标本一直很稀少，而且由于被包裹沉积物挤压，要么残缺不全，要么难以研究。一些来自澳大利亚的新生代化石蛇具有已灭绝类群——巨蛇科的脊椎形态特征，该类群在冈瓦纳大陆从中白垩世（森诺曼阶）到始新世广泛分布，在晚白垩世时期也抵达了欧洲。尽管有着如此漫长的历史，但从最著名的物种纳拉库尔特沃纳姆比蛇中，已知的头骨部分只有大约一半，而其他物种为数不多的已知颅骨元素，也几乎没有为系统发育关系提供更多证据。关于它们的关系和进化意义，已经提出了相互矛盾的假说，要么认为它们是具有许多祖先（类似巨蜥或沧龙）特征的基干蛇类，要么认为它们是与蛇类起源关系不大的进步（大吻鳞类）真蛇类。在此，我报告了来自澳大利亚北部渐新世晚期和中新世早期的两件归入尤尔伦古尔蛇的部分骨骼，它们合起来几乎代表了完整的头骨和下颌骨。保存异常完好的头骨提供了新的证据，将尤尔伦古尔蛇与沃纳姆比蛇及其他巨蛇科联系起来，证伪了大吻鳞类假说的预测，并支持将巨蛇科排除在包括所有现存蛇类的进化枝之外。
