Fossils and Transitional Forms: Evidence for Macroevolution

0:00Macroevolution is large-scale change, such as whole new groups of living things arising. What is the evidence for it?

0:09Sedimentary rock forms as layers of mud and sand settle and harden, and it holds fossils: the preserved remains or traces of living things.

0:20In undisturbed rock, deeper layers formed first, so they are older. The layers work like a timeline.

0:29Some fossils are transitional forms: not always direct ancestors, but with features of both an older group and a newer group.

0:38Tiktaalik, about 375 million years ago, had fins and gills like a fish, but a neck and limb-like fins like a tetrapod, an animal with four limbs.

0:50Archaeopteryx, about 150 million years ago, had feathers and wings like a bird, but teeth, claws and a bony tail like a dinosaur.

1:01Early whales such as Ambulocetus, about 49 million years ago, had four legs like a land mammal, but ear bones like a whale's, and they swam in water.

1:13The fossil record, all the fossils found so far, has gaps. But gaps do not disprove evolution.

1:21Fossils form only in rare conditions: remains must be buried quickly in sediment, and hard parts like bone and shell last best. Most remains simply decay.

1:33The fossils we do find fit the order evolution predicts: fish before tetrapods, and tetrapods before birds and whales.

1:43Fossil layers show life changing over time, and transitional forms link the groups: strong evidence for macroevolution.