The beginning and end of each chunk of time in the geologic time scale is determined by when some species appeared or disappeared from the fossil record ... The end of the Paleozoic and beginning of ...

3 min read The Cambrian period, part of the Paleozoic era, produced the most ... which left a huge number of fossils. Trilobites had flattened, segmented, plated bodies that helped to protect ...

The Devonian, part of the Paleozoic era, is otherwise known as ... fish that lacked jaws developed a range of bizarre forms. Fossil specimens include species with horseshoe-shaped heads and ...