Chordates, or members of phylum Chordata, possess a backbone.
Answer:
during the Cambrian Period of the Paleozoic Era.
Explanation:
The Paleozoic is the earliest era (of three) of the Phanerozoic Eon and is composed of six geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (in that order from earliest to the latest). Fish first appeared about 530 million years ago during the Cambrian explosion.
<u><em>Chromosomes</em></u> asserts that our genes set the boundaries within which we can operate