The oldest is the Paleozoic Era, which means ‘ancient ... the end-Cretaceous extinction wiped out many major animal groups including every land creature that weighed more than a few pounds.

The Paleozoic era's Silurian period saw animals and plants finally emerge on land. But first there was a period of biological regrouping following the disastrous climax to the Ordovician.

The Environment of Vertebrate Life in the Late Paleozoic in North America: A Paleogeographic Study. By Prof. E. C. Case. (Publication No. 283.) Pp. vi + 273. (Washington: Carnegie Institution of ...

A recent study shows that marine oxygen levels were crucial to the evolution of early Paleozoic trilobite body size, ...

Therapsids formed a wide-ranging group of four-legged animals, with only mammals surviving today. During the late Paleozoic, they played a major role in life on land, long before dinosaurs appeared.

The Devonian, part of the Paleozoic era ... legs to move in shallow waters or even on land. The fish showed other characteristics of terrestrial animals, including ribs, a neck, and nostrils ...