The First Terrestrial Animals
The First Terrestrial Animals |
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The First Terrestrial Animals came up on land in the late Ordovician period, probably around 450 million years ago, although it was during the Silurian Period, probably within 10-20 million years of the arrival of fungi and primitive plants on land in the late Ordovician Period, that land ecosystems included thriving diverse terrestrial species and plants. It makes sense to guess that the earliest terrestrial animals would be some of the very primitive Metazoa (animals) such as one of the worm phyla, perhaps a nematode, a segmented worm (one of the annelida, such as an earthworm), or even a mollusk like a slug, but it is the arthropoda with their hard shells that have left us the oldest fossils of terrestrial animals. There are fossils of trigonotarbids from the more recent strata of the Upper Silurian (The Llandovery Epoch of about 444-428 million years ago). By the later Silurian (414 million years ago) there were already complex terrestrial ecosystems featuring various myriapod arthropods (centipedes and millipedes), and some sort of arthropods that were eating fungi, known only from their fecal pellets (from the Ludlow Epoch, 422-419 mya). The 428 million year old millipede Pneumodesmus newmani is one of the oldest terrestrial animals known from the fossil record. Trace fossils (trackways) from approximately 450 million years ago and genetic evidence suggests other arthropods might have arrived on land much earlier. |
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Links about the Ordovician-Silurian extinction event: 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.
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