The arthropods. Almost six hundred million years ago, long before vertebrates existed, some sea-dwelling animals evolved a hard, armor-like body covering, and things just haven't been the same since.

Did vertebrates evolved from arthropods?

This overwhelmingly strong evidence has always pointed directly to the origin of the vertebrate from some form among the segmented group of invertebrates, annelid or arthropod, in which the original œsophagus had become converted into the infundibulum, and a new mouth formed.

Did arthropods evolve first?

The first fossil arthropods appear in the Cambrian Period (541.0 million to 485.4 million years ago) and are represented by trilobites, merostomes, and crustaceans.