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Agnostids were a group of marine animals that became extinct about 450 million years ago. Agnostid fossils can be found in rocks in many areas around the world. From the fossil remains, we know that agnostids were primitive arthropods-relatives of modern-day insects. However, the fossil information does not allow paleontologists to determine with certainty what agnostids ate or how they behaved. There are several different theories about how agnostids may have lived.

Free-Swimming Predators

First, the agnostids may have been free-swimming predators that hunted smaller animals. It is known that other types of primitive arthropods were strong swimmers and active predators, so it is reasonable that the agnostids may have lived that way as well. And while the agnostids were small, sometimes just six millimeters long, there were plenty of smaller organisms in the ancient ocean for them to prey on.

Seafloor Dwellers 

Second, they may have dwelled on the seafloor. Again, there are examples of other types of primitive arthropods living this way, so it is possible that agnostids did too. On the seafloor they would have survived by scavenging dead organisms or by grazing on bacteria. 

Parasites 

Third, there is the possibility that the agnostids were parasites, living on and feeding off larger organisms. One reason that this seems possible is that there are many species of modern-day arthropods that exist as parasites, such as fleas, ticks, and mites. The agnostids might have lived on primitive fish or even on other, larger arthropods.

文章生词与表达整理

  • Agnostids n. [古生物学]球接子类
  • marine adj. 海生的;海运的
  • extinct adj. 灭绝的,绝种的
  • fossil n. 化石
  • primitive arthropods 远古节肢动物
  • paleontologists n. 古生物学者
  • determine with certainty 准确判定
  • predator n. 捕食者;掠夺者
  • It is known that… 众所周知的是…
  • organism n. 生物体
  • prey on 捕食;掠夺
  • dwell v. 居住;存在于
  • seafloor n. 海底
  • scavenge v. 以…为食
  • graze on 吃(牛羊等吃草)
  • bacteria n. 细菌
  • parasite n. 寄生虫
  • live on 以…为食;靠…生活
  • feed off 从…取食
  • flea n. 跳蚤
  • ticks n. 扁虱 
  • mite n. 螨虫

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