Archaeopteryx, Birds & Dinosaurs
In two articles, I will discuss the relationship between birds and dinosaurs. This is the first one; the second one is A comparison of Birds and Their Ancestral Dinosaurs.
In 1880, Thomas Henry Huxley suggested that birds evolved from dinosaurs.
Huxley based his theory on a comparison of Archaeopteryx, generally considered to be an early bird, and bones from Theropod dinosaurs that were found in the same area. He found striking similarities.
This idea, already then seen with skepticism by his colleagues, later came to be completely discarded. Between 1920 and about 1970, the paradigm was that dinosaurs were cold-blooded, slow and stupid animals, very primitive creatures that could not be closely related to birds at all.
The turning point came during the 1970s-1990s and findings in Manchuria and Mongolia of quite birdlike dinosaurs. They clearly had feathers, which was the first absolute evidence that at least some dinosaurs had feathers. They also showed skeletal similarities with birds and quite evidently they were fast. Feathers also indicate that they were warm blooded - the original purpose of feathers was most probably insulation, to keep warmth inside.
Since then, there are a lot of findings and observations confirming the close relationship between dinosaurs and birds. There are so many fundamental similarities, and so many things we today see as typical for birds that were there already with the dinosaurs, that the closeness can no longer be denied.
According to the present level of knowledge, birds did not only evolve from dinosaurs, they are dinosaurs.
It is justified to assume that Archaeopteryx is the world's most well-known fossil. It is sometimes described as a bird, sometimes not, it all boils down to definitions, but fact is that it triggered the idea that perhaps birds descend from dinosaurs the first time it turned up. It happened 1880, when Thomas Henry Huxley suggested that birds evolved from dinosaurs. He based this theory on a comparison of Archaeopteryx, generally considered to be an early bird, and bones from Theropod dinosaurs that were found in the same area. He found striking similarities.
This is a photo from 1880 of a fossil of Archaeopteryx, the Berlin Archaeopteryx specimen. Legs and feathers were subsequently removed. Totally, 11 fossils of Archaeopteryx have been found. Most of them in Jurassic limestone in Bavaria (about 150 million years old).
Archaeopteryx was a long time considered as the oldest known fossil bird, because it had feathers. In German, it was even referred to as “Urvogel”, meaning “original bird”. This was based on the (erroneous) assumption that only birds had feathers. Only in the beginning of this century, findings of other feathered and birdlike fossils of about the same age in China have changed that view. Archaeopteryx is now increasingly re-classified as a dinosaur, but not a bird. This makes sense, because Archaeopteryx has some characteristics that are not birdlike. Indeed, they contradict the criteria for being a bird. The fact that it had feathers does not alone make it a bird, since it has now been understood that feathers existed before the evolution of birds. Archaeopteryx also had wings, but the skeletal structure doesn't support flight (although it had started to change in that direction), as it does in birds, so it is unclear if it could fly. Further, it had hollow bones with air sacs, so had at least some traditional non-avian dinosaurs as well. (More about that in a forthcoming article.)
If feathers, wishbone, three-fingered hands, and robust forelimbs would make Archaeopteryx a bird, it certainly wasn't the first one. There were older species with these characteristics. However, according to the present standards of classification, there are further criteria for making something a bird, and these criteria are not satisfied.
Archaeopteryx had teeth, a bird has not. It also had a long tail, while in birds, the tail has become very short, which is probably necessary for efficient flight. Further, birds have fused fingers, while Archaeopteryx could move each finger individually, and its fingers had claws. We are talking about hands, a part of the wings. Birds have claws, but not on the forelimbs.
So, if Archaeopteryx was not a bird (Aves), what was it then? Well, just as all birds, it certainly was a dinosaur, most likely a transitional form between non-avian dinosaurs and birds; a dinosaur on its way to become a bird. If its line is the origin of birds is a matter of dispute, but I doubt that it was. Many parallel lines may have evolved and only one survived. Archaeopteryx is scientifically important, however, for our understanding of as well birds as dinosaurs and how theropod dinosaurs became birds.
The word “archaeopteryx” was coined by palaeontologist Christian Erich Hermann von Meyer. He based it on Ancient Greek ἀρχαῖος (arkhaîos, “ancient” or “primitive”); and Ancient Greek πτέρυξ (ptérux, “wing”).
This discussion continues in A comparison of Birds and Their Ancestral Dinosaurs.
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