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Birds and Dinosaurs

by Eva Amsen

Piquing the curiosity of everyone’s inner 14-year old boy, dinosaurs were in the news several times this month. Particularly, their connection to modern day birds is being discussed by several groups around the world.

First, an October 5 news release from the University of North Carolina rebuts an earlier claim that fossilized dinosaur structures from China had feathers. They examined the “feathers” from the fossils of these Cretaceous dinosaurs, the Sinosauropteryx, more closely, and concluded that they were decomposing flesh. The theory of feathered dinosaurs had led people to believe that currently living birds are descendants of dinosaurs, but these findings show that the link between birds and dinosaurs is not as close as it would seem.

“We all agree that birds and dinosaurs had some reptilian ancestors in common,” said Feduccia, professor of biology in UNC’s College of Arts and Sciences. “But to say dinosaurs were the ancestors of the modern birds we see flying around outside today because we would like them to be is a big mistake.”


This sounds a lot like the misconception often brought forward by creationists who don’t want to accept that humans have “descended from monkeys”. They haven’t: humans and monkeys just have a common ancestor, a species that later evolved down separate branches, eventually leading to humans, and several simians with varying degrees of similarity between them. Birds and dinosaurs also have a common ancestor, but this part of the evolutionary tree branched off earlier than the human/monkey branch, and the dino part of it went extinct.

 

Of course it’s far more complex, but this illustrates the general idea. There is no direct line from dinosaurs to birds, and no direct line from monkeys to humans.
Another strong argument in the case against the feathered dinosaur was the fact that the fossil in question 25 million years after the first known bird, Archeopteryx, already existed. It is highly unlikely that feathers evolved again, through another route, millions of years later on a different continent.
This new knowledge puts another news release from the same month in an interesting light: Chinese researchers reported that another Cretaceous dinosaur from China flew using a set of four wings. The four-winged dino, the Microraptor gui is not the same species as the now known to be unfeathered Sinosauropteryx, but it is from the same time and continent which are thought to have been unlikely to inhabit feathered dinosaurs. Did it fly without feathers? Is it from a different period? Did it evolve seperately from the birds?

To summarize the story so far: although dinosaurs and birds share a common ancestor, it is not true that birds, of which …. is the oldest known kind, evolved directly from the groups of species we now call dinosaurs. (I’m deliberately wording this very carefully. You’ll find out why later on.)

The wrong concept of the evolution of birds/dinosaurs is illustrated here, with humans/monkeys added in the commonly thought of wrong way as well.

In this figure, I tried to illustrate humans branching off from monkeys, where monkeys stay somewhat consistent as a group over time (indicated by the word “monkeys” appearing at different points in time). Similarly, I illustrated the conventional birds-descend-from-dinosaurs idea by a direct line between the two. Why is this “wrong”? It seems like the same kind of figure, and the general phrases “dinosaur” and “monkey” are very misleading, but you have to keep in mind that humans do not descend from monkeys as we know them, and neither do birds descend from any of the species of dinosaurs that we know off. The “common ancestor” in both branches of the tree is not known. Yet…

To make matters more complicated, or perhaps clearer, another bird/dinosaur story appeared in the news recently. Fossilized remains of a dromaeosaurid, a “lizard-like” dinosaur (raptor), were found in South America, in an earth layer that, based on its age, indicated that this dinosaur walked on the continent of South America after that had already split off from other continents. This means that an ancestor of the dromaeosaurids lived on the supercontinent before it split, more than 145 million years ago in the Jurrassic era, before the Cretaceous era.
Dromaesaurids and the earliest birds have a very similar bone structure, and probably have a common ancestor. If the line of dromaesaurids is pushed back, that means that birds may have split off from dinosaurs earlier than we thought.

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