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. Strictly speaking, all fossils are transitional, since all species are the transition between their ancestors and their descendants. Whether or not we know what they are the transition between does not affect that. But regardless, there are many fossils that definitively link two genuses, orders, and classes. The following is a short list:
- Archaeopteryx is an intermediate form between theropod dinosaurs and modern birds. It had teeth and claws like a dinosaur, and avian feathers like a modern bird, large wings but sideways shoulder joints, along with several features common to both.
- Tiktaalik is 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.
- Orrorin tugenensis, Ardipithecus kadabba and ramidus, Australopithecus anamensis, afarensis, africanus, bahrelghazali, and garhi, Kenyanthropus platyops, Paranthropus aethiopicus, boisei, and robustus, Homo habilis, rudolfensis, ergaster, antecessor, cepranensis, and rhodesiensis, for most of which there have been found several fossils, represent the chain of successive transitions between Sahelanthropus tchadensis and Homo sapiens sapiens (modern humans).
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.