最早期的陆地生物 (terrestrial animals)， 应该属于某些非常原始的后生动物 (Metazoa)， 譬如说蠕虫动物门中的线虫类、节状蠕虫（环节动物门之一，如蚯蚓），或甚至像蛞蝓这类的软体动物，都是蛮有可能性的猜测。可是从生物化石研究所得知，目前地球上最古老的陆地生物非节肢动物 (arthopoda) 莫属。
有些蛛形类 (trigonotarbids) 的生物化石，是在近代的希留利亚纪初期 (Upper Silurian) 的地层发现的（志留纪大约在4亿4400-4亿2800万年前）。在希留利亚纪后期（4亿1400万年前），已经有复杂的陆地生态系统，出现不同的多足节肢动物（蜈蚣和千足虫），和某种吃菌类植物的节肢动物，对此种节肢动物的认知，仅可从他们颗粒状的排泄物来判断。
在化石研究记载里，已有4亿2800万年之久的千足虫－纽氏呼气虫 (Pneumodesmus newmani) 是最早期的陆地动物。有4亿5000万年之久的足印化石和基因研究证明 (genetic evidence) 显示，可能有其他的节肢动物更早登上陆地。
连结网页
- The Kentucky Geological Survey has one of the best sites about early terrestrial animals.
- David Winter’s very fine page about the various times animals have moved up on land.
- Here is an abstract of a paper by Gregory Retallack and Carolyn Feakes suggesting trace fossils from Pennsylvania indicate land animals in the late Ordovician, about 450 million years ago.
- Ken McNamara and Paul Selden’s fine article from a 1993 issue of NewScientist about early colonization of land habitats in the late Ordovician.
- This overview of the Chelicerate group, given to us by the University of Bristol, indicates that some Eurypterids could get up and crawl about on land.
连结网页
- The Kentucky Geological Survey has one of the best sites about early terrestrial animals.
- David Winter’s very fine page about the various times animals have moved up on land.
- Here is an abstract of a paper by Gregory Retallack and Carolyn Feakes suggesting trace fossils from Pennsylvania indicate land animals in the late Ordovician, about 450 million years ago.
- Ken McNamara and Paul Selden’s fine article from a 1993 issue of NewScientist about early colonization of land habitats in the late Ordovician.
- This overview of the Chelicerate group, given to us by the University of Bristol, indicates that some Eurypterids could get up and crawl about on land.