One of the lesser-known geologic spans in the earth's history, the Ordovician period (448-443 million years ago) didn't witness the same burst of evolutionary activity that characterized the preceding Cambrian period; rather, this was the time when the earliest arthropods and vertebrates expanded their presence in the world's oceans. The Ordovician is the second period of the Paleozoic Era (542-250 million years ago), preceded by the Cambrian and succeeded by the Silurian, Devonian, Carboniferous and Permian periods.
Plant Life During the Ordovician Period
As with the preceding Cambrian, evidence for terrestrial plant life during the Ordovocian period is maddeningly elusive. If land plants did exist, they consisted of microscopic green algae floating on or just underneath the surface of the water, along with equally microscopic early fungi. However, it wasn't until the ensuing Silurian period that the first terrestrial plants appeared for which we have solid fossil evidence.
Vertebrates. Practically all you need to know about vertebrate life during the Ordovician period is contained in the "aspises," especially Arandaspis and Astraspis. These were two of the first jawless, lightly armored prehistoric fish, measuring anywhere from six to 12 inches long and vaguely reminiscent of giant tadpoles. The bony plates of Arandaspis and its ilk would evolve in later periods into true skeletons, further reinforcing the basic invertebrate body plan. Some paleontologists also believe that the numerous, tiny, worm-like "conodonts" found in Ordovician sediments count as true vertebrates; if so, these may have been the first vertebrates on earth to evolve teeth.
Plant Life During the Ordovician Period
As with the preceding Cambrian, evidence for terrestrial plant life during the Ordovocian period is maddeningly elusive. If land plants did exist, they consisted of microscopic green algae floating on or just underneath the surface of the water, along with equally microscopic early fungi. However, it wasn't until the ensuing Silurian period that the first terrestrial plants appeared for which we have solid fossil evidence.
Vertebrates. Practically all you need to know about vertebrate life during the Ordovician period is contained in the "aspises," especially Arandaspis and Astraspis. These were two of the first jawless, lightly armored prehistoric fish, measuring anywhere from six to 12 inches long and vaguely reminiscent of giant tadpoles. The bony plates of Arandaspis and its ilk would evolve in later periods into true skeletons, further reinforcing the basic invertebrate body plan. Some paleontologists also believe that the numerous, tiny, worm-like "conodonts" found in Ordovician sediments count as true vertebrates; if so, these may have been the first vertebrates on earth to evolve teeth.
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