Vertebrate: any Chordate animal with

• a cranium
• usually a segmented vertebral column

Fish, amphibians, reptiles, birds, mammals

Phylum Chordata

a group of animals with 4 diagnostic features, present at some stage of the life cycle (embryo, larva, adult, or all):

Some chordates are invertebrates.

• A notochord, a stiff but flexible, unsegmented rod, running lengthwise along the middle of the organism, providing support for the skeleton, not found in any other organisms.
• dorsal, single, tubular nerve cord
• perforated pharynx, gill slits
• tail

Chordate Chronology

1. First chordates - Cambrian, 500 million years ago
2. Fish 450 MYA
3. Amphibians 360 MYA
4. Reptiles 300 MYA
5. Dinosaurs 250 MYA
6. Birds 150 MYA
7. Mammals 100 MYA

These dates are assigned based on the first appearance of these organisms in the stratigraphic column. The inference then is that these animals came into existence over a long period of time in roughly an order from simple to complex. Young earth creationists, who believe that the earth was created a few thousand or perhaps tens of thousands of years ago, must explain the observed presence of different fossils in different layers by some other means.