Fossils are the remains of organisms from the distant past embedded and preserved in the earth's crust. Fossils may be any sort of organism, from a single-celled bacteria to a tree leaf to a dinosaur, and may be anywhere from ten thousand to several billion years old. They usually consist of parts of the organism which were mineralized during the organism's lifetime, such as bones and exoskeletons.
A transitional fossil is one that bridges the evolutionary gap between two previously discovered organisms. A fossil which is transitional between two species will typically have some features of both, and several features which are developed halfway between the two.
Creationists claim that there is a lack of transitions in the fossil record in order to argue against evolution, but this is far from the truth. There are thousands of transitional forms. The following are some definitive examples of transitional forms between major extinct genuses and modern ones:
- Archaeopteryx, an intermediate form between theropod dinosaurs and modern birds, has both reptilian teeth and avian feathers, large wings but sideways shoulder joints, along with several features common to both.
- Tiktaalik, an intermediate form between fish and amphibians. It had gills and scales like a fish, lungs and rib bones and a movable neck like an amphibian, and fish-like fins with limb bones and a fully functional wrist joint with simple fingers.
Fossil Record Gaps
The argument that there are gaps in the fossil record, used by apologists, basically amounts to a claim that there are no transitional forms between the transitional forms we've already discovered.
- misunderstands what constitutes a transitional feature.
- ignores the large number of fossils found.
- denies the transitions those fossils represent.
- is ignorant of the fossilization process.
- creates an expectation of accuracy far beyond what is necessary to illustrate transition.
- dismisses definitive examples of transitional forms, focusing on the ones that remain undiscovered.
- theoretically moves the goalposts every time a "gap" is filled, as each discovery of a transitional form creates two new gaps.
- is profoundly ignorant of the mechanisms of evolution itself.