最早期的陸地生物 (terrestrial animals) 應該屬於某些非常原始的後生動物 (Metazoa)， 譬如說蠕蟲動物門中的線蟲類、節狀蠕蟲（環節動物門之一，如蚯蚓），或甚至像蛞蝓這類的軟體動物，這些猜測都蠻有可能性的。可是從生物化石研究所得知，目前地球上最古老的陸地生物非節肢動物 (arthopoda) 莫屬。
有些蛛形類 (trigonotarbids) 的生物化石是在近代的希留利亞紀初期 (Upper Silurian) 的地層發現的（志留紀大約在4億4400-4億2800萬年前）。在希留利亞紀後期（4億1400萬年前）已經有複雜的陸地生態系統，出現不同的多足節肢動物（蜈蚣和千足蟲），和某種吃菌類植物的節肢動物，對此種節肢動物的認知僅可從他们顆粒狀的排泄物來判斷。
在化石研究記載裡，已有4億2800萬年之久的千足蟲－紐氏呼氣蟲 (Pneumodesmus newmani) 是最早期的陸地動物。有4億5000萬年之久的足印化石和基因研究證明 (genetic evidence) 顯示，可能有其他的節肢動物更早登上陸地。
友誼網頁連結
- 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.
友誼網頁連結
- 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.