ps418

Today's debunking will focus on what the 'God and Science' article has to say about the pelves of Archaeopteryx, theropod dinosaurs, and alligators. The article states:

The unavoidable conclusion is that whoever wrote this article simply has not bothered to look at theropod pelves and compare them to that of Archaeopteryx. In fact, the pelvis of Archaeopteryx and other early birds is essentially identical to those of dromaeosaurid theropods, and are dramatically different from those of all modern birds.



Obviously, the pelvis of Archaeopteryx is most similar to those of Unenlagia and Tyrannosaurus, both of which are theropods. Also obvious is that these three pelves are morphologically more similar to each other than any of them are to the alligator pelvis.

Now, for comparison, let's look at the modern bird pelvis. The picture below is far from perfect for illustrating the pelvis, but its the best I could find on the internet. Sorry! This is a chicken, and it has the same pelvis morphology you see in most other birds.



Note the entirely different pelvic structure.

In contrast to theropods and Archie, and the other earliest birds, in modern birds the ischium and ilium are fused together, and several vertebrae are fused both to each other and to the ilium, forming a structure known as a pygostyle. Of course, most of the theropods, Archie, and the earliest birds all lack a pygostyle, and instead have rather long tails.

In contrast to theropods and Archie, and the other earliest birds, modern birds lack the distinctive pubic foot. This is the triangular, posteriorly-oriented process on the distal end of the pubis. Also, note that in contrast to some theropods, Archie, and the other earliest birds, where the pubis and ischium are at a ~45 degree angle to each other, in modern birds the pubis is reduced to a thin strip of bone parallel to the ischium.

Note also the opening in the bird pelvis, immediately posterior to the acetabulam, where the legs articulate with the pelvis. This opening is called the ilioischiadic foramen. It is formed by the rear of the illium bending down and then fusing with the ischium. In theropods, Archie, and the other earliest birds, this is absent, because the ischium and illium are not fused.

I think this is more than sufficient to demonstrate that the claim that "the pelvic bones of the theropod dinosaurs look nothing like that of . . . Archaeopteryx" is complete nonsense. However, I still would like to scan and post some illustrations of other theropod and early bird pelves to complete the picture, particularly those from the Liaoning theropod specimens.

Patrick

caravelair

thanks so much, patrick! (i hope you don't mind me calling you that. my name is aidan. hi.)

one of the claims i'm curious about is this one:

anybody have information on this?

Coragyps

Patrick's link above:

Feduccia, A., 1999. 1,2,3,=2,3,4: accomodating the cladogram. Proceedings of the National Academy of Sciences 96, 4740-4742.

should be online here. This is the "pro" position, and I don't know enough about the subject to know where to find alternate views.

ps418

Actually, there is a paper in the same issue of the PNAS by Wagner and Gauthier giving their solution to the problem. This is on my to-read list currently.

1,2,3 = 2,3,4: A solution to the problem of the homology of the digits in the avian hand


Not at all.

Patrick

ps418

Another ref I need to get is:

Frietson et al, 2003. An old controversy solved: Bird embryos have five fingers. Trends in Ecology and Evolution 18 (1): 7-9.

According to this post to CMNH, the Frietson et al article:

One point to keep in mind is that the assertion that theropod manus digits are digits I-III is based on an assumption of homology among several fossil dinosaur taxa which show the loss of digits, which of course implies the common descent of those taxa. So, although it is perfectly reasonable for Feduccia et al to use this as an argument, for creationists it is a bit problematic. Also keep in mind that while we can watch birds develop literally under a microscope, we can not do this for fossil theropods, so we are left comparing adult fossils with living embryos, which introduces uncertainty. That said, I need to read and think a bit more before I can state my own best guess on this issue.

Patrick

ps418

From Caraveleir's article:

Oh, surprise-- another whopper of an error that could only be made by someone who's never bothered to actually look at a theropod or bird foot.

The feet of both birds and theropods are tetradactyl, that is, they have four digits, not three. Birds have three forward-pointing toes, and one toe (the hallux) that is retroverted. In modern birds, this allows for a perching grasp. Granted the finer points of anatomy can get lost, but can't these people even count digits properly?

In fact, except for the retroverted digit I, known as the hallux, the hindlimb of Archaeopteryx and other eary birds are basically identical to those of dromaeosaurid theropods. And contrary to the quoted creationist, no one to my knowledge, not even Feduccia, has questioned the homology of the theropod and avian pedal digits. According Dingus and Rowe (The Mistaken Extinction, p 211):

Patrick

ps418

I have some better illustrations for you, caravelair.



This is the pelvis of Deinonychus, a Cretaceous dromaeosaurid theropod.



This is the pelvis of Archaeopteryx.



And this the pelvis of an eagle, and is representative of modern bird pelves.

Obviously, the claim that "the pelvic bones of the theropod dinosaurs look nothing like that of . . . Archaeopteryx" could only emanate from a mind that is in deep, irrational denial of the facts.

Patrick

Nic Tamzek

When that godandscience article was written the author was already scrambling to deal with newer fossils. Here's another one: Give 'em this:

http://research.amnh.org/vertpaleo/dinobird.html

MrDarwin

Just wanted to add that the book Mesozoic Birds just came in at my library, and all I can say is wow. It ain't cheap, but it is full of really, really good stuff.

It will be fun to watch the creationists scramble to keep up with all the new fossil birds, dinosaurs, bird-like dinosaurs and dinosaur-like birds that are being described over the next few years.

ps418

According to the Reasons to Believe commentary:

The author, Fazale Rana, doesn't know what he's talking about. Convergence refers to the evolution of similar characters from dissimilar ancestors, which is obviously not something that the anti-evolutionists at RTB can accept. So, as far as I can tell, RTB is just saying: 'They're similar because God created them that way,' or 'They're similar because they're similar,' but for some reason they use the word convergence.

After all, bats, birds and pterosaurs are all fliers that are convergent in some ways, but they are not anywhere near as morphologically similar to each other as are theropods and the earliest birds. Humans and birds are both bipedal tetrapods, but we don't have any difficulty distinguishing between them. You can instantly differentiate their fossils based on skeletal anatomy. Explaining the similarities of Caudipteryx and theropods as the result of convergence (perhaps from very un-bird-likeTriassic archosaurs as in Fedducia's model) would require a degree of convergence totally unprecedented, and strains credibility well past the breaking point. Theropods are not to early birds as Tasmanian wolves are to canids.

Rana has it wrong just like the other article does. The articles he cites are about the theropod and avian forelimbs, not the hindlimbs. The forward-pointing digits in both the theropod foot are indeed II-III-IV, with digit one being reversed or partly reversed in theropods and birds. I checked a few of Feduccia's paper, and as far as I can tell, he does not question that in both birds and theropods, the forward pointing digits are II-III-IV.

Patrick