“西里龍”（恐龍的一個近親）的一個新屬和新種的一個近乎完整的骨架的發(fā)現(xiàn),，將三疊紀中期爬行動物化石記錄中一些松散環(huán)節(jié)聯(lián)系了起來。新發(fā)現(xiàn)的種是“鳥頸類主龍”（Ornithodira）已知最早的成員之一，這個鳥類分支還包括恐龍和飛龍,，其生活年代可以追溯到兩大“祖龍”類別“鳥頸類”和“鱷魚類”分化后不久,。
齒系和其他特征表明,，“西里龍”并不像人們可能預料的那樣是兩條腿的食肉動物,，而是體型更大的食草動物。但其真正的意義在于年代早,，這表明,，我們對恐龍和飛龍演化的最早階段仍然知之甚少。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 464, 95-98 (4 March 2010) | doi:10.1038/nature08718
Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira
Sterling J. Nesbitt1,2,9, Christian A. Sidor3, Randall B. Irmis4,5, Kenneth D. Angielczyk6, Roger M. H. Smith7 & Linda A. Tsuji8
The early evolutionary history of Ornithodira (avian-line archosaurs) has hitherto been documented by incomplete (Lagerpeton 1) or unusually specialized forms (pterosaurs and Silesaurus 2). Recently, a variety of Silesaurus-like taxa have been reported from the Triassic period of both Gondwana and Laurasia, but their relationships to each other and to dinosaurs remain a subject of debate3, 4, 5. Here we report on a new avian-line archosaur from the early Middle Triassic (Anisian) of Tanzania. Phylogenetic analysis places Asilisaurus kongwe gen. et sp. nov. as an avian-line archosaur and a member of the Silesauridae, which is here considered the sister taxon to Dinosauria. Silesaurids were diverse and had a wide distribution by the Late Triassic, with a novel ornithodiran bauplan including leaf-shaped teeth, a beak-like lower jaw, long, gracile limbs, and a quadrupedal stance. Our analysis suggests that the dentition and diet of silesaurids, ornithischians and sauropodomorphs evolved independently from a plesiomorphic carnivorous form. As the oldest avian-line archosaur, Asilisaurus demonstrates the antiquity of both Ornithodira and the dinosaurian lineage. The initial diversification of Archosauria, previously documented by crocodilian-line archosaurs in the Anisian6, can now be shown to include a contemporaneous avian-line radiation. The unparalleled taxonomic diversity of the Manda archosaur assemblage indicates that archosaur diversification was well underway by the Middle Triassic or earlier.
