Fossil

A transitional fossil is one that bridges the evolutionary gap between two organisms. A fossil which is transitional between species A and species B will typically have some features of both. For instance, Archaeopteryx has both reptilian teeth and avian feathers.

Creationists like to claim that there is a lack of transitions in the fossil record, and use this as a claim against evolution.

Creationists also tend to misundersand the nature of transitionals, and ask questions like "what good is half a wing?"