Scientist says ostrich study confirms bird 'hands' unlike those of dinosaurs

University of North Carolina News Services ^ | August 14, 2002 | DAVID WILLIAMSON

[forsnax5]

CHAPEL HILL -- To make an omelet, you need to break some eggs. Not nearly so well known is that breaking eggs also can lead to new information about the evolution of birds and dinosaurs, a topic of hot debate among leading biologists.

Drs. Alan Feduccia and Julie Nowicki of the University of North Carolina at Chapel Hill have done just that. They opened a series of live ostrich eggs at various stages of development and found what they believe is proof that birds could not have descended from dinosaurs. They also discovered the first concrete evidence of a thumb in birds.

[VadeRetro]

Note, however that Feduccia's embryological evidence doesn't work with the argument that the Chinese feathered dinos were "bird" descendants re-evolving dinosaurhood. Or, at least it forces you to draw some kind of line through the theropods and say, "These are bird descendants" and "These, through convergent evolution, are a cousin branch of real dinosaurs."

Unless the observation of vestigial fingers (the wrong ones) on early theropods is wrong. Or unless Feduccia's embrylogical study is wrong.

The trend of the evidence, at least until Feduccia's study came out, has been very much away from Feduccia's hypothesis. It's just impossible to draw the kind of line between birds and dinosaurs that should be there if the split happened as far back as he puts it.

[syriacus]

Far more likely is that birds and dinosaurs had a much older common ancestor, he said.

Should this statement make Sankar Chatterjee happy?

[Junior]

TUCvER bump.

[forsnax5]

From your post:

It's just impossible to draw the kind of line between birds and dinosaurs that should be there if the split happened as far back as he puts it.

From the article:

How can a bird hand, for example, with digits two, three and four evolve from a dinosaur hand that has only digits one, two and three? That would be almost impossible.

Dueling impossibilities!

So far, the only embryo evidence for the article's hypothesis is from ostrich embryos. Suppose the next embryo experiment with another species shows just the opposite.

Perhaps there are two totally different lines of birds extant today?

[VadeRetro]

Dueling impossibilities!

Some conflicts come from bad data. In such cases, further study typically resolves the conflict, only to have a new one spring up nearby.

[bert]

keep in mind the source.

Left wing wannabe scientists from the Carolina Blue zone can't be believed.

[VadeRetro]

Perhaps there are two totally different lines of birds extant today?

There's some basis for lumping birds in two piles but it seems to be a beauty-contest judging call.

[VadeRetro]

Should this statement make Sankar Chatterjee happy?

Chatterjee's Protoavis will remain controversial unless and until somebody finds a better-preserved specimen.

[jennyp]

Ich kann nicht so gut Deutsch lesen anyway.

The articles are in English, but the August issues' TOC & abstracts are already on line, and nothing by Feduccia is to be seen. Curious.

[forsnax5]

There's some basis for lumping birds in two piles ...

Interesting link. I was expecting that the ratites (ostriches, et al) might be a much older group than the volants (flyers), but no such neat divisions seem to appear.

Also, it appears that Feduccia has had his nose in this issue right along:

Whether modern birds are most closely related to dinosaurs or crocodylian ancestors is a point of current debate. The orders of extant birds appear to have arisen close to each other in time, although their age is uncertain, having been estimated to be about 60 million years old or over 90 million years old based on morphology and fossils (see Feduccia, 1996) and molecular data (Sibley and Ahlquist, 1990; Hedges et al., 1996), respectively.

[Gladwin]

I wish there were some pictures posted somewhere of these embryos. It would clear up a lot.

http://www.ulb.ac.be/sciences/biodic/EImOiseau0002.html

Which are chicken embryo pictures. Most of the tissues don't appear differentiated. At 72 hours, you can see the spine and head starting to form, at most.

[AndrewC]

Which are chicken embryo pictures.

Nice pix, but quite incomplete. Here is one more to provide a more complete data set.

The "three-minute" chicken embryo

[AndrewC]

The articles are in English, but the August issues' TOC & abstracts are already on line, and nothing by Feduccia is to be seen. Curious.

© Springer-Verlag 2002 Short Communication The hand of birds revealed by early ostrich embryos Alan Feduccia1, and Julie Nowicki1 (1)

Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA

Abstract. The problem of resolving the homology of the digits of the avian hand has been framed as a conflict between paleontological and embryological evidence, the former thought to support a hand composed of digits I, II, III, because of similarity of the phalangeal formulae of the earliest known bird Archaeopteryx to that of Mesozoic pentadactyl archosaurs, while embryological evidence has traditionally favored a II, III, IV avian hand. We have identified the critical developmental period for the major features of the avian skeleton in a primitive bird, the ostrich. Analysis of digit anlagen in the avian hand has revealed those for digits/metacarpals I and V, thus confirming previous embryological studies that indirectly suggested that the avian hand comprises digits II, III, IV, and was primitively pentadactyl.

---

E-mail: Feduccia@bio.unc.edu Phone: +1-919-9623050 Fax: +1-919-9623690

[AndrewC]

I was expecting that the ratites (ostriches, et al) might be a much older group than the volants (flyers), but no such neat divisions seem to appear.

Well, then this might interest you.

This is from "The Complete Mitochondrial Genome of Rhea americana and Early Avian Divergences" by Anna Härlid, Axel Janke, Ulfur Arnason

Volume 046, Issue 06, pp 0669-0679
Journal of Molecular Evolution

Phylogenetic analysis of the complete cytochrome b genes of seven avian orders placed the Passeriformes basal in the avian tree with the Struthioniformes among the remaining Neognathae. These findings challenge the commonly accepted notion that the most basal avian divergence is that between the Palaeognathae and Neognathae.

[forsnax5]

Phylogenetic analysis of the complete cytochrome b genes of seven avian orders placed the Passeriformes basal in the avian tree with the Struthioniformes among the remaining Neognathae. These findings challenge the commonly accepted notion that the most basal avian divergence is that between the Palaeognathae and Neognathae.

Wow! It would take a bit of practice to read that paragraph out loud. ;)

It appears that Palaeognathae has replaced Ratitae in the lexicon of avian superorders:

Ratitae (Palaeognathae)

A group comprising the flightless birds, including the ostrich, kiwi, and emu. They have long legs, heavy bones, small wings, a flat breastbone, and curly feathers. These birds are thought to have descended from a variety of flying birds and are not representatives of a single homologous group.

Here's some more information that turned up with Google:

Orders of the Superorder Palaeognathae

• Ratitae: Struthioniformes (Ostrich)
• Ratitae: Rheiformes (rheas) sometimes grouped with Struthioniformes
• Ratitae: Casuariiformes (cassowaries, emus, casuaries) sometimes grouped with Struthioniformes
• Ratitae: Aepyornithiformes (elephant birds) extinct
• Ratitae: Dinornithiformes (moas and Anomalopteryx) extinct
• Ratitae: Apterygiformes (kiwis)
• Tinamiformes (tinamous)

[Nebullis]

Pulling up an old thread with a new thought.

So far, the only embryo evidence for the article's hypothesis is from ostrich embryos. Suppose the next embryo experiment with another species shows just the opposite.

There's a published study by Hans Larsson and GÜnter P. Wagner
Pentadactyl ground state of the avian wing

The issue of the homology of bird fingers with those of pentadactyl amniotes has been a topic of contention for nearly 200 years. Data from the fossil record and phylogenetic systematics ascribe bird digit homologies to digits I, II, and III of pentadactyl amniotes while embryological evidence supports digital homologies of II, III, and IV. Using a molecular marker specific for condensation competent mesenchymal cells, we describe a pentadactyl arrangement of prechondrogenic digital anlagen in the wings of stage 29 chick embryos. Only the middle three anlagen develop into mature fingers. This pattern supports the hypothesis that bird fingers develop from digital anlagen II, III, and IV of pentadactylous amniotes. In addition, this result rejects a model assuming a shift in the primary axis in bird digit development and shows that a prechondrogenic digital anlage has been maintained in the bird lineage for at least 220 million years since the last known pentadactylous ancestor of the lineage. Such a vestige suggests that strong constraints are maintaining a pentadactyl ground state in amniotes. J. Exp. Zool. (Mol. Dev. Evol.) 294:146-151, 2002.

I don't think that a shift in digit selection under control of a gradient is a difficulty. But the fossil sequence needs to show it, too. Not knowing dinosaur development, the digital anlage is an open question, however.

[drlevy88]

Why would an embryo HAVE to recapitulate "evolution" -- assuming that "evolution" is how the creature came to be? Is there a sequencer in there somewhere?

[Doctor Stochastic]

It doesn't seem to be a requirement, but it does seem to happen. The only thing I would guess (without lots of research) is that earlier stages of the embryo are more undeveloped than the later stages. It's possible (a guess again) that the mechanism that moves the jawbones into the ears (of mammals) happens later than the formation of the bones themselves.

[drlevy88]

Haeckel's "recapitulation" embryo drawings were later shown to have been faked IIRC. Whatever the merits of the theory of evolution in particular cases, it appears all too often to be an intellectual sieve; an atheistic article of faith as it were. A lot of the "scientific" material on it appears to differ sharply on "how these creatures descended by evolution" but without exception remain united on "these creatures DID descend by evolution." After a point, that kind of attitude remains philosophically defensible only if one sticks doggedly to atheistic axioms.

[Doctor Stochastic]

Embryology has advanced in the last 80 years. The gills become vocal chords (in humans) and the jawbones become earbones in mammals.