Discovering Religion: Episode 8 – Archaeopteryx
Another important evolutionary milestone was the transition of therapod dinosaurs into feathered birds. In 1861 the first complete specimen of Archaeopteryx was announced, only two years after Charles Darwin published On the Origin of Species. And over the following years, nine more fossils of Archaeopteryx have surfaced.
Darwin was fortunate enough to see his Theory of Natural Selection vindicated by this half avian half reptilian animal, believed to have lived 150 million years ago, predating modern birds by some 65 millions years. Although Archaeopteryx is regarded as one of the most important discoveries in paleontology, creationists continue to downplay its significances by claiming it was only a bird and denying all evidence of its reptilian nature. So, lets first explore the characteristics that allow the avian classification of Archaeopteryx, and then we will examine in detail its purely reptilian features.
Feathers are the key diagnostic feature of birds and this is one of the main criteria for the avian classification of Archaeopteryx, as no other modern animal has feathers. However, starting from 1987 and continuing to 2009, many species of dinosaurs have been found displaying feathers. Further strengthening the link between dinosaurs and modern birds.
Caudipteryx, discovered in China in 1998, is prime example of a feathered dinosaur:
“Caudipteryx is a wonderful little animal, its got these downy-like feathers covering all its body and on the backs of its arms its got fairly short, stiff feathers in the sense of what we would call a modern bird feather. And at the end of the tail is a fan of feathers as well. When you look at the Caudipteryx feathers under a microscope its quite clear that you can see the rakus, you can see the barbs, and in some places you can even just make out what you think are the barbules.
Caudipteryx I think shows us a transitional stage where these dinosaurs have now developed another purpose for feathers. Dinosaurs throughout their history were animals that were very visual. They were animals that displayed in a lot of ways. So if they wanted to attack a mate, they would have a big crest or a big frill on their head.”
An opposable hallux, or big toe, is the second avian feature found in therapods, a group of meat eating bipedal dinosaurs to which Archaeopteryx belongs; although, this feature is not observed in other varieties of dinosaurs.
The furcula, or wishbone, is structure we commonly associate with birds. However, a furcula is known to be a key skeletal structure in therapods such as the raptor:
“In that its holding its arms up close against its body. The prey item doesn’t think its as close as it is so to speak. So they have a stereotype motion where they go down and forward, grab their prey, up and back. Down and forward, up and back. That’s the flight stroke. That’s exactly the way birds fly today. And we always wondered, how do you get power on the upstroke? They actually make this transformation in a muscle called the supracoracoideus that shoots the arm forward, and in birds its actually lifts the arm up, but the motion made here is exactly the flight stroke.
So these guys are grabbing prey items at a considerable distance from their bodies, they prey item struggles in their grasp, and as a consequence they stabilize the shoulder joint by fusing the two clavicles together to make a wishbone. And they had to pull the prey back to them. That’s power on the upstroke, before you’re flying. And so virtually all details of the flight stroke originate before flight. And that’s the best part about the fossil record. There is no way you would look at a flying bird today and go, obviously the forelimb came from a raptorial organ used to seize and secure prey. No way you would guess that. That’s only the information you can get from the fossil record.”
At first is was unclear if Archaeopteryx contained pneumatic bones, that is, bones containing air-sacs — a feature of modern birds. However, two of the Archaeopteryx specimens do show evidence of vertebral pneumaticity in the cervical and anterior thoracic vertebrae, thus confirming the continuity between the pneumatic systems of non-avian theropods and living birds.
Now lets exam the reptilian features of Archaeyopteryx, there are 17 in total. The Premaxilla and maxilla Do not contain a keratinized covering. Therefore, Archaeopteryx has no bill. Because all modern-day birds have either beaks or bills covered with keratin, Archaeopteryx cannot be considered a modern bird.
Archaeopteryx, as well as other dinosaurs, have nasal openings that are positioned far forward, separated from the eye. This is not the case for birds. In birds the each half of the brain appears small and bulbous. However, because the cerebellum of the Archaeopteryx is so enlarged, it spreads forwards over the mid-brain and compresses it downward. Thus the shape of the brain is not like that of modern birds, but rather an intermediate stage between dinosaurs and birds.
In birds the skull attaches to the neck from below. However, the skull of Archaeopteryx attaches from the rear, as in dinosaurs.
Vertebrae in the trunk of birds are always fused. However, Archaeopteryx has free vertebrae, which allow enhanced flexibility, a dinosaur characteristic.
Archaeopteryx has cervical vertebrae with simple concave articular facets, which closely resembles that of archosaurs. In contrast, the cervical vertebrae of birds have a saddle-shaped surface.
Archaeopteryx has slender ribs that do not articulate, or for a joint, with the sternum. Birds on the other hand have shorter, thicker ribs with joints that do articulate with the sternum.
Gastralia are ribs found in the abdominal dermis. These structures are present in 5 skeletal specimens of Archaeopteryx. This kind of rib is typical of reptiles, although absent in birds.
Archaeopteryx has the deltoid ridge of its humerus facing anteriorly, as do the radial and ulnar condyles. This is typical of reptiles but not found in birds.
Archaeopteryx has metacarpals, or hand bones, which are free and flexible, a characteristic of reptiles. However, in birds the metacarpals are always fused together.
Archaeopteryx has six bones in its sacrum, which are the vertebrae that attach the spine to the pelvic girdle. This is the same in reptiles, especially ornithopod dinosaurs. However, the bird sacrum covers between 11-23 vertebrae. Therefore, modern birds and the Archaeopteryx differ considerably on this point.
An elongate pubis, directed backward is a common feature of birds as well as some theropod dinosaurs. However, the pubic shafts of Archaeopteryx has a plate-like, slightly angled transverse cross-section which not found in any other archosaurs.
Archaeopteryx has a long boney tail with many free vertebrae up to the tip, without a pygostyle on the end. However, birds have a short tail and the caudal vertebrae are fused to give the pygostyle, seen here. Therefore, the tail of Archaeopteryx appears much more reptilian than avian.
Archaeopteryx has a fibula that is equal in length to the tibia in the leg. This again is a typical character of reptiles. In birds the fibula is shortened and reduced.
Archaeopteryx has metatarsals, or foot bones, that are unfused and free. In birds the metatarsals are fused. However, in modern bird embryos, the foot bones are initially separate. This raises the question as to why a the bird embryo should produce separate bones and then later fuse them? Reptilian features found in bird embryos which are later suppressed as the embryo matures are difficult facts anti-evolutions have trouble explaining.
Archaeopteryx has teeth, but modern birds do not. However, bird embryos do form tooth buds, yet teeth are never produced within the adult bird. Some birds have ridges in their bill, but there is no connection to embryonic tooth buds, since the ridges also form in areas of the bill where no tooth buds previously exist. The expression of tooth buds in the bird embryo has a simple evolutionary explanation, since evolution predicts the ancestors of birds possessed teeth — a characteristic now suppressed in modern birds. Again, creationism cannot explain why an embryo should express characteristics that are never realized within the adult organism. There were some ancient birds that contained teeth within their bill, such as Hesperornis, which lived 89-65 million years ago.
Archaeopteryx has claws located on 3 unfused digits of its wings. No modern adult bird has 3 claws, nor do they have unfused digits. In the embryonic stage almost all birds exhibit claws, however, this trait is lost by the time the bird leaves the egg. As we saw with the loss of tooth buds and the fusion of metatarsals, the loss of claws is the 3rd embryonic trait that displays the reptilian ancestry of birds.
As we have seen, there are 17 individual characteristics that displays the reptilian nature of Archaeopteryx; however, there are only 4 characteristics that identify it as a bird and all 4 of these are shared among many other species of dinosaur as well.
Yet, creationist continue to foolishly deny the reptilian features of Archaeopteryx and vehemently profess no intermediate species have ever been found: “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 is supposed to be billions of them.”
Without question, animals can adapt to their environments and overtime evolve into new and different species. However, evidence for evolution is not only found in the fossil record, there is mountains evidence found within currently living animal species, including ourselves.