鸟脚亚目

而且它们很大：有时超过4米长，大到足以捕杀一头成年鸟脚亚目食草恐龙。

And they were big : sometimes more than four metres long . That is certainly large enough to take on an adult ornithopod .

当然除非生态系统的顶级掠食者——即是能捕杀成年的鸟脚亚目食草恐龙的——并不完全是恐龙。

Unless , of course , the top predator of the system - the one that could hunt down adult ornithopods - was not a dinosaur at all .

白垩纪被称为鸟脚亚目食草恐龙其地位相当于斑马和羚羊——每部有关非洲大草原的纪录片中被捕杀的种群。

The Cretaceous equivalent of zebra and antelopes - the victim species in every wildlife documentary about the dramas of the African savannah - were herbivorous dinosaurs called ornithopods .

但不总是这样，当庄姆海勒与博依德对犹他州出土的白垩纪年幼的鸟脚亚目食草恐龙的化石进行检查时，他们在一副骨架上发现了看上去像是遭受现代鳄鱼撕咬的痕迹。

But not always . When Ms Drumheller and Mr Boyd examined the bones of juvenile upper-Cretaceous ornithopods dug up in Utah they saw marks on one skeleton that looked suspiciously like those modern crocodiles inflict when biting and tearing at their prey .

这颗牙不是很大，其尺寸表明牙齿的主人不超过一米五（约五英尺）这样的掠食者本不能捕食一头成年鸟脚亚目食草恐龙。

It was not a large tooth . Its size suggests the animal which made it was no more than a metre and a half ( about 5 feet ) long . Such a predator would have been unable to take on an adult ornithopod .