scientists have discovered in china the first complete skeleton of a pivotal（关键的，中枢的） ancestor of earth's largest land animals – the sauropod（蜥脚类动物） 1. the new species, tentatively（暂时地） 2 yizhousaurus sunae, lived on the flood plains around lufeng in the yunnan province of south china about 200 million years ago. the species helps explain how the iconic four-footed, long-necked sauropod dinosaurs evolved. unlike the 120-foot-long, 100-ton sauropod giants that came later, yizhousaurus was about 30 feet in length, but it shows all of the hallmarks of later sauropods: the beginning of a long neck, a 3 skeleton and four-legged 4. it also comes with an intact fossilized 5 – which is very rare and crucial for understanding its place in the evolution of sauropods.
"sauropods have these big bones but their 6 are very lightly constructed and also very small," said paleontologist（古生物学者） sankar chatterjee of texas tech university. chatterjee presents the discovery on sunday, oct. 31 at the annual meeting of the geological society of america in denver.
yizhousaurus's skull is broad, high and 7, less than a foot long with a short snout（鼻子，猪嘴） , eye 8 on the sides for scanning enemies. it has an unusually wide and u-shaped 9, in top view, like that seen in later camarasaurus, said chatterjee. numerous serrated and spoon-shaped teeth of the upper and lower 10 would 11 and slide past each other for cutting plant material during feeding. the sturdy teeth and raised neck let the animal very easily nip small branches from treetops and then chew the plant material.
"once the plant food was ingested, a 12 mill（胃齿臼） in the stomach probably provided further mechanical 13 of the plant," chatterjee explained. 14 the animal was well adapted to a life of eating plants to support its large body.
besides its telltale（报警的，泄密的） physical features, yizhousaurus was also found in revealing company. a half century ago spectacular 15 of prosauropod dinosaurs such as lufengosaurus were discovered at the same location. this makes sense, since most paleontologists are of the opinion that prosauropods gave rise to sauropods, despite the fact that the transition has been very vague, chatterjee said.
"this is why this new one (yizhousaurus), may bridge this gap," he said.
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