據(jù)12月11日的《科學(xué)》雜志報道說,，在新墨西哥州新近發(fā)現(xiàn)的一種早期的恐龍屬于獸腳亞目食肉恐龍世系，該世系的恐龍中最終演化出了T. rex（或譯：霸王龍）,。這一發(fā)現(xiàn)提示，最早的恐龍在全世界有著廣泛的分布,，也許它們起源于南美洲,。 與侏羅紀(jì)和白堊紀(jì)的恐龍化石的記錄相比，有關(guān)三疊紀(jì)晚期（距今大約有2億3000萬年）的恐龍生活的畫面則顯得相當(dāng)粗略,。 我們知道,，恐龍在那個時候已經(jīng)分化成為三個主要的族群：獸腳亞目食肉恐龍、蜥腳亞目食草恐龍和鳥臀目恐龍,。但是,，來自這一時期的恐龍化石一般較為稀有、且碎裂而不完整,。
Sterling Nesbitt及其同僚現(xiàn)在描述了來自三疊紀(jì)晚期的幾副幾近完整的獸腳亞目恐龍的骨架,。他們將其命名為Tawa hallae。這一命名是根據(jù)普埃布洛印地安人部落的描述太陽神的Hopi（霍皮）字眼Tawa以及業(yè)余古生物學(xué)家Ruth Hall的名字組合而成的,。 該種恐龍體型小且體重輕,，并與其前輩恐龍共有相互混雜的特征，如骨盆特征,；它又有其同期恐龍和后輩恐龍所專屬共有的 “異祖性”衍征,，如有氣體填充的脊椎空間。 研究人員還分析了已知三疊紀(jì)恐龍中的進(jìn)化關(guān)系,。 這種關(guān)系的復(fù)雜性和多樣性提示,，北美的獸腳亞目恐龍可能并非地方性特產(chǎn)，且早期恐龍很容易地跨越各個大陸而擴(kuò)散各地，它們可能起源于現(xiàn)在的南美洲,。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
