Exploring Transitional Fossils

This interactive module allows students to examine fossils of fish, tetrapods (four-limbed animals), and their transitional forms.

Both fish and tetrapods are types of vertebrates. Fish were the first vertebrates to appear in the fossil record, more than 500 million years ago. Because tetrapods appeared in the fossil record later, about 365 million years ago, scientists have hypothesized that tetrapods evolved from fish. This hypothesis is supported by transitional forms, which have features of both fish and tetrapods, that appeared in the fossil record between 390 million and 360 million years ago.

In this Click & Learn, students examine fossils of prehistoric vertebrates, including transitional forms, and compare their anatomical features. They also compare these features to those of the coelacanth, the only living member of an ancient group of lobe-finned fish.

The accompanying worksheet guides students’ exploration.