Transitional fossil

So many intermediate forms have been discovered between fish and amphibians, between amphibians and reptiles, between reptiles and mammals, and along the primate lines of descent that it often is difficult to identify categorically when the transition occurs from one to another particular species. A transitional fossil (incoherently misnamed "missing link" by Creationists) is a fossil of an organism that has traits from multiple evolutionary stages.

Creationist denialism
Science has NEVER found a genuine transitional form that is one kind of animal crossing over into another kind — either living or in the fossil record — and there's supposed to be BILLIONS of them! Proponents of creationism claim that "evolutionists" have had "over 140 years to find a transitional fossil and that nothing approaching a conclusive transitional form has ever been found" — despite the discovery of Archaeopteryx (a transitional form between maniraptoran dinosaurs and basal (primitive) birds, and among the best examples of evolution) only two years after Darwin published The Origin of Species.

Creationists say that we "never saw evolution happen". This is not just false, but since they brought it up, we should probably address that we never saw any of the bullshit mentioned in the Bible and the Quran happen, either. Oops.

Impossible standard of evidence
Finding transitional forms never impresses creationists, and for a very simple reason.

If transitional form B — fitting snugly between known species A & C — is found, creationists will suddenly demand that "actual" transitional forms — now between A & B and B & C — be located, lest (they declare) the existence of transitional forms to begin with is to be considered bunk.

Apparently, the only thing that would satisfy them is a complete, unbroken set of generation-by-generation fossils of every organism that ever lived in a direct line of descent from the first bacterium to Charles Darwin's grandfather.

But no matter how many fossils are found, this demand is perpetually extended by the creationists all the way down to the individual level, looping us back around from the geological timespans that formation of species require to the shortsighted comparison of parent-child differences, where obviously no "transitional form" occurs (since we can safely assume that no further lines of descent exist between your own parents and yourself).

While this clearly absurd and impossible standard of positive evidence will never be met — nor could it be — creationists struggle to find even a single paleozoic panda as negative evidence against evilution. Oops.

The misconception of "missing links"
The term "missing link" is just an obsolete (and rather weasely) synonym for "transitional form". It is generally avoided in scientific discussions as it is suggestive of several misunderstandings about evolution — many of which Creationists subscribe to, of course. These include:


 * The old idea of a Great Chain of Being, in which there is a linear progression "upward" presumably ending with humans, just underneath gods and other divine beings. Concepts of evolution since Darwin recognize, to the contrary, that evolutionary change often involves branching, and that unguided evolution has no preferred "direction".


 * The idea that the fossil record is the only type of evidence which can establish a connection between different life forms. The preponderance of the evidence for evolutionary connections always has been found in living things from the present ("neontology") rather than solely in the fossil record ("palaeontology"). Comparative study of DNA since the elucidation of its structure is just one of the remarkable new lines of investigation.


 * Another mistaken idea is that there is a scandalous gap in the fossil record especially with regard to human evolutionary history. While a hundred years or more ago, there were very few fossils of human precursors, even as early as the 19th century, there were famous fossils such as Neanderthal (Homo neanderthalensis) and Java man (Homo erectus), and the number has dramatically increased as explorations have concentrated on productive regions in Africa (as suggested by Darwin, but largely ignored at first) since the mid-20th century.


 * The final mistaken idea is that there is precisely one form: the missing link, which makes the connection between the past and the present. Evolution is understood ever since Darwin as an ongoing process in which one can expect many changes, sometimes very small, which can be fully appreciated only in their places in a web of relationships over stretches of time.


 * Another problem is that evolution denialists will simply claim that there is another missing link even when a missing link was found. Let's just say that modern humans are Human 2.0 and some early form of "humans" is called Human 1.0. Evolution denialists would claim that we need to find the missing link of Human 1.5. If Human 1.5 is discovered, that creates two new missing links, Human 1.25 and Human 1.75 that evolution denialists would say need to be discovered. If those two missing links are discovered, then the four new missing links Human 1.125, Human 1.375, Human 1.625 and Human 1.875 would need to be discovered. And so on. The only way to satisfy evolution denialists would be to have a record of all "humans" or even all life that has ever existed. Even if every fossil organism were discovered and categorized, there would still be "missing links" because likelihood that bones become fossilized is very rare since fossilization requires a very specific set of geological conditions.

Examples of transitional fossils
Since then, many other transitional forms, such as Ambulocetus and Pakicetus (land mammals to marine cetaceans), and Tiktaalik and Acanthostega (fish to tetrapods) have been found.