新发现的食肉恐龙改变了进化树

Paleontologists, aided by amateur业余的 volunteers, have unearthed¹发掘 a previously² unknown meat-eating dinosaur³ from a fossil bone bed骨层 in northern New Mexico, settling a debate about early dinosaur evolution, revealing a period of explosive diversification⁴多样化，变化 and hinting at how dinosaurs⁵ spread across the supercontinent Pangaea盘古大陆，泛大陆. A live embargoed⁶被禁止的 webcast网路广播 with the scientists will be held in advance of publication for credentialed受到信任 reporters on Dec. 9. See details below.

The description of the new species, named Tawa after the Hopi word for the Puebloan sun god, appears in the Dec. 10 issue of the journal Science in a paper lead-authored by Sterling⁷ Nesbitt, a postdoctoral博士后的 researcher at The University of Texas at Austin's Jackson School of Geosciences. Nesbitt conducted the research with his colleagues while a graduate student at Columbia University's Lamont-Doherty Earth Observatory⁸ and the American Museum of Natural History.

The fossil bones of several individuals were recovered, but the type specimen⁹ is a nearly complete skeleton骨架，骨骼 of a juvenile青少年，幼稚的 that stood about 28 inches (70 cm) tall at the hips¹¹ and was about 6 feet (2 meters) long from snout鼻口部 to tail. Its body was about the size of a large dog, but with a much longer tail. It lived about 214 million years ago, plus or minus增减 a million. The specimens¹² are remarkable¹³ because they show little sign of being flattened¹⁴ during fossilization石化，僵化.

Tawa is part of a group of dinosaurs known as theropods兽脚类食肉恐龙, which includes T. Rex and Velociraptor迅猛龙. Theropods for the most part ate meat, walked on two legs and had feathers. Though most went extinct by 65 million years ago, some lineages survived to spawn¹⁵产卵 modern birds.

One of Tawa's most important contributions to science has to do with what it says about another dinosaur, Herrerasaurus黑瑞龙, the center of a lively debate since its discovery in Argentina in the 1960s. Herrerasaurus had some traits特性，特质 in common with theropods—including large claws, carnivorous食肉的 teeth and certain pelvic骨盆 features—but lacked other theropod traits such as pockets in vertebrae椎骨，脊椎 for airsacs肺泡. Some paleontologists claimed it was so unusual it was outside the evolutionary¹⁶ tree of theropods, or even of dinosaurs. Others placed it among the earliest theropods.