Myelin appears suddenly in vertebrates, animals with backbones that arose 500 million years ago. Not a trace of it is found in the ancestral line that preceded the arrival of vertebrates.

Because we're a member of the group, it's easy to see vertebrates as the pinnacle of evolution, a group capable of producing bats, birds, and giant whales in addition to ourselves.

Tunicates are the sister group of vertebrates, meaning that they shared a common ancestor hundreds of millions of years ago. They are a diverse subphylum of invertebrate marine animals that ...

Fish: Vertebrates that live in water and breathe using gills; Fish are defined as vertebrates (meaning they have a backbone) that live in water and use gills to breathe.

Scarce evidence indicates that key evolutionary steps for jawed vertebrates occurred during or before the Silurian period, 444 million to 419 million years ago. Fossil finds pull back the curtain ...

Scientists have long puzzled over the gap in the fossil record that would explain the evolution of invertebrates to vertebrates. Vertebrates, including fishes, amphibians, reptiles, birds, mammals ...