The sea lamprey is an ancient jawless fish.

七鳃鳗是一种没有颚的古老鱼类。

Jawless fishes invaded the ocean, sporting points, prongs, and finally, fins.

无颌鱼入侵海洋，运动尖头、叉子，最后还有鳍。

Several of these classes are specific types of fish, for example: jawless fish, like lampreys and hagfish, and cartilaginous fish, like sharks and rays.

这些纲类的一些便是鱼类，比如：无颚纲鱼形动物，像七鳃鳗、盲鳗和软骨纲鱼，像鲨鱼和魔鬼鱼。

Forming a notochord like those still found in some of today's jawless fish.

形成脊索，就像今天仍然在一些无颌鱼中发现的脊索一样。

Because, osteostracans are among the few jawless fish to have a bony internal skeleton, or endoskeleton.

因为，osteostracans 是少数具有骨质内部骨骼或内骨骼的无颌鱼之一。

Somewhere around China, a fish developed jaws, and its descendants drove jawless fishes, sea scorpions and branching plankton to extinction.

在中国的某个地方，一条鱼长出了颚，它的后代使无颚鱼、海蝎子和分支浮游生物灭绝。

Like modern lampreys and hagfish, conodonts were jawless fish, and they were one of the earliest and most successful groups of vertebrates.

像现代的七鳃鳗和盲鳗一样， 牙形刺是无颌鱼，它们是最早和最成功的脊椎动物群之一。

The jawless fish, known as Lechriaspis, was killed by three distinct puncture wounds to the head -- puncture wounds made by crushing claws.

这种被称为 Lechriaspis 的无颌鱼是被头部的三个明显的刺伤杀死的——这些刺伤是由爪子挤压造成的。

Sea levels were high, and the continents were surrounded by vast, shallow seas, full of exotic creatures like rugose corals, crinoids, and jawless fish.

海平面很高，大陆被广阔的浅海包围，充满了奇异的生物，如长皱纹珊瑚、海百合和无颌鱼。

And these sea scorpions had a pair of appendages that were more like paddles, which allowed them to swim, a lifestyle that put them in direct competition with jawless fish and cephalopods.

这些海蝎子有一对更像桨的附肢，可以让它们游泳， 这种生活方式使它们与无颌鱼和头足类动物直接竞争。