Here is our response to the Limusaurus paper. It was recently rejected by nature, not for any technical reason but because it was considered not to be of sufficient interest/importance.

We have uploaded it at the nature precedings citable archive, because we think it is important there is a quick and citable reply that unlike Xu’s proposal, is consistent with the view of the larger community of theropod paleontologists, namely, that tetanuran digits still are I, II, III. We are preparing a longer paper on this topic.

Keep up the great work!

Peter from Gansu, China

Thanks for stopping by. I remember Feduccia was claiming that the evo-devo research he had cited showed a 2-3-4 digit arrangement, and for him, that clearly disproved dinosaurian ancestry (In the interest of full disclosure, I am a former invertebrate paleobiologist, so it’s not really clear to me why Feduccia thought this was relevant.).

Appreciatively yours,

John

In a typical phylogenetic analysis one simply identifies characters that differ among species, more or less assuming that you know what it is you should be comparing. But here, obviously, the question was where to start in making comparisons. We couldn’t simply have a character, “Manus digit I, with no phalanges (0) one phalange (1) or two phalanges (2)” without being sure we knew which digit is the first one in each tetanuran.

This is a problem that is largely ignored by morphologists, with a few exceptions such as Martin Ramirez, Olivier Rieppel, and my former student Maureen Kearney. The approach we took is one that is more common in molecular sequence analysis, such as the program POY by Ward Wheeler, where alternative primary homology statements are compared against one another, to see how congruent different primary homology hypotheses are with other characters. We therefore coded ceratosaurs and each major group of tetanurans as either 1-2-3 or 2-3-4 and compared the results. If birds are indeed 2-3-4 then it is far simpler for all tetanurans to be 2-3-4 than the alternative.

Now to bring it around to missing links – at the level of character analysis there are certain taxa, such as Limusaurus, that change primary homology statements by showing some kind of intermediate condition. In some sense these forms can be considered to provide missing links between homologies.

In closing I need to add that Xu Xing was the primary author and the person who realized first what was going on with this animal, but because he is in the field right now he isn’t available for interviews, so I have been the spokesman for the paper this week.

Beg your pardon? I’ve dropped by here before, and with good reason. Consistently Carl has had the best entries I have seen with regards to evolutionary biology. His latest on Limusaurus is a classic example for two reasons:

1) It is quite succinct and therefore gets to the point.

2) Carl does a much better job than, for example, a certain “evo-devo” biologist blogger in explaining why this discovery is important to the average, interested layperson.

As for my previous comment, Alan Feduccia is an ornithologist at, if I’m not mistaken, University of North Carolina, Chapel Hill. He is also among the very few who still doubt the dinosaurian ancestry of birds. A few years ago I heard Feduccia give a talk in which he claimed he had “evo – devo” evidence refuting the now robust hypothesis first proposed by the late John Ostrom (although, to be historically correct, the very first one was none other than Thomas Henry Huxley) that birds are living descendants of small theropod dinosaurs.

To be more precise, you should have said non-avian dinosaurs, since there was one monophyletic theropod dinosaur lineage that not only did survive, but indeed, has flourished; birds.

@ Carl -

This may be one of the best posts I’ve seen from you pertaining to paleobiology. Too often both the general public – and unfortunately, even some publicity-hungry scientists too – tend to be a bit “obsessed” with “missing links”, when it’s really more interestitng to look at certain lineages just to note how “bushy” they are, as for example, the terrestrial “primitive”
placental mammal – seagoing cetacean transition, or the for more classic one – I suppose – showing the gradual transition from lobefinned fishes like Eustenopteron to the “fishapod” Tiktaalik, through “primitive” tetrapods like Acanthostega and Icthyostega.

BTW I believe I heard Alan Feduccia making a big fuss over which digits had fused, claiming that he had some important “evo – devo” evidence refuting work by Ostrom, Gauthier et al. with regards to the dinosaurian ancestry of modern birds. I wonder what he’ll say after he reads the Xing Xu et al. paper in Nature.

For Subramanyam: hoatzin chicks have claws on their wings, but they are deeply nested among other birds that do not. So they have reversed the situation. Note that evolution doesn’t always “lose” features, though: genetic controls evolve that suppress the development of features whose genes are still hanging around in the genome. (Hence, among other things, the occasional dolphin with hindlimbs.)

1) Birds could not have evolved from crurotarsians, either;
2) Birds could not have evolved from basal archosaurs;
3) Birds could not have evolved from basal birds (Archaeopteryx, Confuciusornis, etc.).

So there you have it.

http://www.eurekalert.org/pub_releases/2009-06/osu-drn060809.php

Anyone read the original paper this refers to and have comments?

I’m not saying I disagree with it, I just need to read the paper.

I’m MORE interested in the fact that Limusaurus is a toothless, beaked, stubby-armed, long-legged CERATOSAUR.