据12月11日的《科学》杂志报道说，在新墨西哥州新近发现的一种早期的恐龙属于兽脚亚目食肉恐龙世系，该世系的恐龙中最终演化出了T. rex（或译：霸王龙）。这一发现提示，最早的恐龙在全世界有着广泛的分布，也许它们起源于南美洲。 与侏罗纪和白垩纪的恐龙化石的记录相比，有关三叠纪晚期（距今大约有2亿3000万年）的恐龙生活的画面则显得相当粗略。 我们知道，恐龙在那个时候已经分化成为三个主要的族群：兽脚亚目食肉恐龙、蜥脚亚目食草恐龙和鸟臀目恐龙。但是，来自这一时期的恐龙化石一般较为稀有、且碎裂而不完整。
Sterling Nesbitt及其同僚现在描述了来自三叠纪晚期的几副几近完整的兽脚亚目恐龙的骨架。他们将其命名为Tawa hallae。这一命名是根据普埃布洛印地安人部落的描述太阳神的Hopi（霍皮）字眼Tawa以及业余古生物学家Ruth Hall的名字组合而成的。 该种恐龙体型小且体重轻，并与其前辈恐龙共有相互混杂的特征，如骨盆特征；它又有其同期恐龙和后辈恐龙所专属共有的 “异祖性”衍征，如有气体填充的脊椎空间。 研究人员还分析了已知三叠纪恐龙中的进化关系。 这种关系的复杂性和多样性提示，北美的兽脚亚目恐龙可能并非地方性特产，且早期恐龙很容易地跨越各个大陆而扩散各地，它们可能起源于现在的南美洲。（生物谷Bioon.com）
生物谷推荐原始出处：
Science 11 December 2009:DOI: 10.1126/science.1180350
A Complete Skeleton of a Late Triassic Saurischian and the Early Evolution of Dinosaurs
Sterling J. Nesbitt,1,2,*, Nathan D. Smith,3,4 Randall B. Irmis,5,6 Alan H. Turner,7 Alex Downs,8 Mark A. Norell1
Characterizing the evolutionary history of early dinosaurs is central to understanding their rise and diversification in the Late Triassic. However, fossils from basal lineages are rare. A new theropod dinosaur from New Mexico is a representative of the early North American diversification. Known from several nearly complete skeletons, it reveals a mosaic of plesiomorphic and derived features that clarify early saurischian dinosaur evolution and provide evidence for the antiquity of novel avian character systems including skeletal pneumaticity. The taxon further reveals latitudinal differences among saurischian assemblages during the Late Triassic, demonstrates that the theropod fauna from the Late Triassic of North America was not endemic, and suggests that intercontinental dispersal was prevalent during this time.
1 Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA.
2 Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA.
3 Committee on Evolutionary Biology, University of Chicago, Chicago, IL 60637, USA.
4 Department of Geology, Field Museum of Natural History, Chicago, IL 60605, USA.
5 Utah Museum of Natural History, 1390 East Presidents Circle, Salt Lake City, UT 84112–0050, USA.
6 Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112–0102, USA.
7 Department of Anatomical Sciences, Stony Brook University, Health Science Center T-8 (040), Stony Brook, NY 11794, USA.
8 Ruth Hall Museum of Paleontology, Ghost Ranch Conference Center, Abiquiu, NM 87510–9601, USA.
