Animals with backbones are called vertebrates. They include reptiles, amphibians, fish, birds, and mammals.
Most of the Mesozoic and Cenozoic rocks (except Quaternary) in Illinois have been removed by erosion. As a result, the vertebrate fossils found in our state are restricted mainly to Paleozoic and Quaternary rocks.
The Paleozoic vertebrate fossils are fish teeth, scales, and bony plates, a few lizards, and amphibians. The Quaternary vertebrates included many formerly common but now extinct animals, such as mammoths and mastodons. Many forms still live in this region, such as horses, cattle, deer, and humans.