Talk:Dinosaur-bird connection

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Contents 1 Are some dinosaurs secondarily flightless? 2 Move? 3 Archaeopteryx and deinonychosaurs 4 Gizzard 5 Thermopolis Archie & "Protoavis" 6 "dinosaur" does not refer to birds 7 Phylogenetic challenge to the coelurosaur hypothesis of bird origins 8 Good Books on topic

[edit] Are some dinosaurs secondarily flightless?

Cladistics neither supports nor denies the neoflightless hypothesis -- which is not a phylogenenic hypothesis per se. John.Conway 12:19, 15 September 2006 (UTC)

I edited the text accordingly, refering only to the phylogenetic position of Archaeopteryx w.r.t birds and deinonychosaurs. --Ollivier 12:51, 17 September 2006 (UTC)

[edit] Move?

Thanks for this long overdue page. Before formally submitting a proposal, I'd like to discuss here whether this page should be moved to "Origin and evolution of birds" or somesuch. Such an article does not exist, though it would be more inclusive, and the present title is kinda redundant with Feathered dinosaurs. Presently, there is no real place to discuss the Cretaceous radiation of birds really, i.e. how Confuciusornis, Gansus, the Hesperornithes, the Enantiornithes and "stuff" like Gargantuavis go together (and then throw in "secondary flightless theropod-like birds"), but that issue is crucial for getting an adeqate picture of avian evolution. Dysmorodrepanis 10:14, 30 September 2006 (UTC)

Maybe a single page treating both the origin of birds and their evolution in the Mesozoic would become too long. Much can be said about both topics... So, sure I would support the creation of a page devoted to the Cretaceous bird radiation, but I think it would be best to make it separate from the debates regarding Archaeopteryx and its dinosaurian relatives, in order to keep both pages short enough to be easy to read. --Ollivier 21:02, 30 September 2006 (UTC)

[edit] Archaeopteryx and deinonychosaurs

Mayr et. al. (2005) showed that the Archaeopteryx specimen they described possesses the hyper-extendible second toe previously found in deinonychosaurs. This character brings Archaeopteryx and deinonychosaurs together and suggests that deinonychosaurs were birds that evolved from Archaeopteryx. Also, therizinosaurs, alvarezsaurids, ornithomimosaurs, and oviraptorosaurs may also be birds, since they lived after Archaeopteryx. Thus, update the section titled "Are some dinosaurs secondarily flightless?".

Mayr, G.; Pohl, B. & Peters, D. S. (2005). A well-preserved Archaeopteryx specimen with theropod features. Science 310(5753): 1483-1486.

The second toe proves not really much. Deinonychosaurs and birds (Paraves) were the closest relatives anyway and by the late Jurassic had just barely diverged enough to be considered separate (also, consider the lack of a robust pre-Late Jurassic fossil record for either). Like feathers, the hyperextendible second toe (AKA "raptor claw" but not necessarily with the claw) seems to be a feature that pops up every now and then all over the lineage. For the time being, I put the other "birdish" theropods in the section, but suffice to say that if there is one lesson from the last 10 years' research, it is that neither flight nor feathers are useful to determine how "avian" some theropod was. Snout and caudal vertebrae are much more useful, and these characteristics suggest that the bird-like theropods may be better seen as secondarily flightless non-avian theropods. The "secondarily flightless birds" hypothesis is basically a relic of those pre-Microraptor days. There is now hardly a gap large enough in the fossil record for some early avian to "branch back" into the "mainstream" theropod lineage, which looks not a t all like an evolutionary "tree" anymore but rather like some thorny tangle of shrubbery.

Speaking of shrubbery, of course one should never say Ni. But the evidence for some dinos being secondarily flightless birds as is accepted at present is a far cry from what it was around 1999. Dysmorodrepanis 16:48, 3 October 2006 (UTC)

Nomingia is a case in point: it has a pygostyle, but that is very "primitive" - most likely too primitive for a Late Cretaceous derivate of Early Cretaceous birds as presently known. The "Jeholornithiformes" and Omnivoropteryx suggest that it cannot be completely ruled out, but the evidence is against it as it would require de-fusion of the caudal vertebrae - theoretically possible, but utterly improbable as far as anyone can say. For the time being, it seems safe to assume that every step towards a pygostyle and a beak the different early avian lineages made was all but irreversible and that secondarily flightless birds should reflect this. Hesperornis does for certain, even though it seems to have lost and re-evolved teeth! Dysmorodrepanis 16:56, 3 October 2006 (UTC)

Still, the paper is good and importatn; it now seems that hyperextensibility of pedal digit II was something which popped up here and there among theropods and thus it can be assumed that the MRCA of birds and non-avian theropods had it at least in an incipient state. Put paper into ref section and discussed implications thereof in article.

BTW I finally got me "Mesozoic Birds" and it confirms my suspicion: most "true" avian (as opposed to paravian) autapomorphies are found in the skull. Witmer's discussion of "Protoavis" is remarkable fair and lucid (he still thinks it's at least dubious and prolly a chimera, but he does not reject it out of hand as many do). Dysmorodrepanis 16:53, 15 October 2006 (UTC)

[edit] Gizzard

The gizzard does not provide evidence for the bird-dinosaur connection as it is a character shared with crocodiles.--MWAK 06:42, 15 October 2006 (UTC)

[edit] Thermopolis Archie & "Protoavis"

The discussion of the Mayr paper suggests that their intent was not really to propose such a hypothesis, but merely to point out some features in the Archie specimen that suggest it indeed belongs to a side branch. I disagree with "Protoavis" not having to do anything with it - in the radical form (i.e. the one that commentators implied Mayr et al supported, which they denied - shall add discussion letters to refs shortly) it would have indeed major bearing as that ultimately boils down to the ancestor of maniraptorans and possibly most theropods even was flying and a "Protoavis"-like critter would fit the bill. That of course implies P. is valid, and my take on that is it isn't. But even then, the most radical possible interpretation would more or less require that something much like P., but a valid form, should lurk in the fossil record, undiscovered as of yet. The fact that "Protoavis" taints everything it touches, so to speak, is probably one of the two main reasons it is left out of Mayr et al's discussion (the other is that they're too careful to explicitly suggest that flight was lost and not gained independently). A major drawback of their phylogenetic analysis is the non-inclusion of most of the "interesting" early birds. The placement of Archie and Confuciusornis on different branches hinges mainly on the diapsid skull. To really raise eyebrows (or possibly not to), Yanornis, Shenzhouraptor, Omnivoropteryx and Liaoningornis, for example, should have been included. In its present state, it is neat, but not earth-shaking. "Archaeoraptor" was earth-shaking - the two components on their own proved ultimately to be far more important on their own than as a composite fake, showing that a) advanced birds existed in the Early Cretaceous, and probably more than one lineage too, and b) that there were 4-winged flying dinos not very closely related to birds - but close enough that their flying ability was somehow connected.
And as I hinted at in the article, a multiple-origin scenario of paravian/theropod flight seems way more parsimonious than the assumption that the Paraves or even most theropods arose from flying ancestors and lost flight multiple times independently (a critter like Protarchaeopteryx, mind you, was well suited to evolve both ways - towards and away from flight. I think these are the actual "transitional" stage: incipient flight capabilities but not flying yet. That would explain things like the pelvis of Rahonavis, which the flying-ancestor model cannot: it is not avian, not even like that of Archie, but it seems to have done fulfilled the same function about as well as in Archie - there are pictures in Geist & Feduccia which speak better than words). The functional diversity of paravian modes of flight around 110-100 mya is hard to reconcile with the latter: even though both Archie and Confuciusornis were incapable of a supporting upstroke, their mode of flight seems to have been radically different as evidenced by their remiges' shape. Add to that Yanornis, Gansus, and the early enantiornithine birds which essentially were "modern" flyers and lived not too far distant in space and time from Confuciusornis - too close in fact to be derived from it - and there you go. Dysmorodrepanis 09:53, 24 October 2006 (UTC)

I noted on the Dutch corresponding page (from which quite some stuff could be translated) that what I was referring to as the "most radical" hypothesis is called the "birds came first" model. See the Dutch page on why a "Protoavis"-like critter is of key importance for that. Again, BFC is not what Mayr et al want to imply - their data is open to both ways of interpretation (widespread loss vs widespread evolution of flight) and the former opens up cans and cans of worms, whereas the latter resolves many questions to satisfaction if you get yourself to let go of flight-in-general as an avian characteristic. Which should not be a problem because it has been done for feathers. "True" avian flight (2-winged, flapping, with pronounced recovery/upstroke and a sternal keel as THE flight muscle attachment) seems to be how flight must be outlined according to current knowledge if one wants to limit it to Aves sensu stricto. And all this coming together is by and large making the evolution of birds, contentious as it may be, more and more an in-your-face to creationists and IDlers - they evolved, that much seems to be sure, by a roughly 50-million-years-long process of trial and error and trying out and rejecting multiple approaches to the challenge, not out of thin air (i.e. by special creation) or according to a pre-laid plan (i.e. by ID), and ultimately only a fairly marginal side branch survived the Big One. It is still not a good model to resolve macroevolution vs microevolution; though it might initialy suggest so, it's really what could be called "mesoevolution", i.e. major changes to a bauplan, but not actually evolution of an entirely novel one (e.g. endo- or exoskeletons from soft-bodied precedessors) . For that, my best guess is that we're indeed dealing with two fundamentally different ways of evolution, with "true" macroevolution being essentially genome/chromosome major-scale rearrangement- and microevolution being essentially point-mutation-driven; Hox genes vs the "proto-feather" mutations in chicken embryos seem to support this. Dysmorodrepanis 10:14, 24 October 2006 (UTC)

Well, you address many things and I'm not quite sure on what points exactly (if any) we are in disagreement :o). Perhaps I can make clear what I think are the basic issues:

1. The Mayr paper doesn't merely suggest, it indicates. Cladistics is an exact science (well... :o) and the exact outcome of the very formal procedure is given. Of course we all know that the next analysis might render an opposite result and given this fundamental incertainty the paper might in the higher sense be a suggestion to at l(e)ast give the hypothesis the attention it deserves. But at itself it is a prima facie indication the hypothesis is true.
2. Of course Archaeopteryx's "belonging to a side branch" simply is the Paulian hypothesis.
3. Indeed a radical BCF-model is emphatically not what Mayr e.a. intended to propose. And their paper itself cannot really be read this way — their data do not support this at all. All the confusion stems from an editorial mistake in the abstract, which spoke of "challenges the monophyly of Aves". This of course doesn't make any cladistic sense — Aves is by definition monophyletic — and inadvertently suggested support for the MANIAC-position.

Anyway, I'm glad you like the Dutch version ;o). It certainly has one quality the English article still lacks: describing the BAND-position, which distasteful as it might be, is still mandatory under Wikipedia NPOV policy :o).--MWAK 11:54, 24 October 2006 (UTC)

I'd still say "suggest" as far Aves in general are concerned - it does "indicate" the findings for the two "early birds" analyzed only, whose placement in the same (i.e. Aves sensu stricto) lineage as of recently became more and more dubious (or, its saurian skull grew more and more in significance seeing that it was fairly different in other Early Cretaceous birds). So the one real suggestion here seems to be to remove Confuciusornithidae from Aves sensu stricto, which is fine with me, or to expand "birds" to include Caudipteryx and Deinonychus, which is not barring further analysis of the taxa I mentioned. I expect that several early birds will turn out to be examples of parallel evolution, and Confuciusornis is a prime suspect here. Dysmorodrepanis 18:05, 24 October 2006 (UTC)

Yes, but we should not forget that the Paulian hypothesis is about two certain factual states: whether certain Maniraptorian groups are more closely related to Archaeopteryx than to other species closer (than Archaeopteryx is) to extant Aves; and whether these groups are secondarily flightless. How Aves should be defined is an entirely different question — one that some would argue is not even scientific. The position of Confuciusornis in relation to species more closely related to extant Aves is for the factual hypothesis not very relevant — unless of course you argue that Confuciusornis is more distantly related than Archaeopteryx! Again a different question is whether Confuciusornis "suffers" from a certain degree of homoplasy and whether including some extant species would have rendered a more traditional result. This will probably soon be done and we'll see what will be the outcome :o).--MWAK 07:54, 25 October 2006 (UTC)

[edit] "dinosaur" does not refer to birds

<<modern birds are dinosaurs and dinosaurs are, therefore, not extinct>>

Not at all. A misuse of language. "dinosaur" never refers to birds. Calling dinosaurs birds is like calling the Japanese Caucasians. Voortle 14:34, 24 November 2006 (UTC)

This is a peoblem stemming from the double use of the word "dinosaur" as both a common name and a scientific name (which is incorrect--it is only a sicentific name). The group Aves belongs within the group Dinosauria according to phylogenetic taxonomy, so Avians are members of dinosauria. Whether or not "birds" are dinosaurs is a matter of how you define the word "bird". If you define "bird" as a member of the clade Aves, then birds must be dinosaurs. If you define bird as "a bipedal animal with feathered wings" and are using a paraphyletic approach, then birds may not be dinosaurs (but many "dinosaurs" would now be birds, like Velociraptor, Oviraptor, etc.)Dinoguy2 15:46, 24 November 2006 (UTC)

Microraptor, not Velociraptor. Evidence for feathers (except maybe "proto-down" in juvies) in top-level predatory theropods is still missing IIRC. Makes not much sense ecologically either - with feathers come novel parasites, and this drawback would be outweighed by flight, thermoregulation or social function; the former two did not apply to large "raptors" and the last could (and likely was) achieved differently, eg by skin flaps like in other "reptiles". "Dinosaur" and "bird" as vernacular terms are form taxa - groups that are diagnosable phenetically, but not phylogenetically.

A recent paper suggests that even the Dinosauria (including Aves) may be poly- or even paraphyletic, but the Dinosaur Mailing List was very skeptical and I would agree with the arguments put forward there. Dysmorodrepanis 21:47, 24 November 2006 (UTC)

"Evidence for feathers (except maybe "proto-down" in juvies) in top-level predatory theropods is still missing IIRC. Makes not much sense ecologically either - with feathers come novel parasites, and this drawback would be outweighed by flight, thermoregulation or social function" Care to tell this to moa, phorosrhachids, kiwi, etc.? No maniraptoran with integumentary impressions has ever been shown to lack feathers. There is not one instance of feathers disappearing along with flight, no matter how modified away from flight the form is, so there is no reason to suspect that even the largest maniraptorans would lack feathers.Dinoguy2 01:11, 25 November 2006 (UTC)

Presence in crown-group taxa of one lineage of a clade does not imply presence in crown-group taxa of another as long as presence in basal taxa - indeed, relationship of lineages inter se, remains unresolved. What can be indeed said is that once acquired, feathers are not easily lost, but are they autapomorphies or not? I'd rather still consider it unresolved. "There is not one instance of feathers disappearing along with flight", Olshevsky/Paul would be overjoyed at reading this ;-), but for the time being, I find it easier ATM to also consider "flight" without any further qualifications (such as "flapping two-winged flight with significant downstroke contribution") to be paraphyletic in theropods. We urgently need a redux of Mayr et al's Science paper with larger taxonomic sample; while ground-breaking, a bitter taste remains for non-inclusion of some key taxa (such as Liaoningornis), and if such a study were conducted, I personally expect the results to be a minor earthquake (or bolide impact if you will). More importantly, a larger avian/NAT sample will allow to evaluate the resultant cladogram, grouping unquestionably monophyletic lineages, which should resolve at least some of the incerta sedes better. Dysmorodrepanis 17:48, 26 November 2006 (UTC)

And once such a paper is published, it's findings can be reflected in the articles here. Howerver, it has not, and the overwhelming consensus in the literature is that "birds are dinosaurs" and that all maniraptora were probably feathered. Dissenting views or variations (Czerkas, Paul, Olshevsky, Martin et al.) should be discussed but not emphasized in favor of the majority view. This is an encyclopedia, and as such should reflect the current status quo. Anything more or less than this is original research.Dinoguy2 17:54, 26 November 2006 (UTC)

Simple phylogenetic bracketing shows that the hypothesis that all Maniraptora had feathers is the most parsimonious. Of course very large maniraptors might have been "naked", but Velociraptor was rather small and hardly a top predator. The main point is that Voortle's premise <<"dinosaur" never refers to birds>> is simply false. And this is not just because some small group of paleontologists uses a different vocabulary; when I showed my 27 months old nephew a picture of a life-size tyrannosaur model, he said just two words: "bird!" and "bite!". Very perceptive of him. ;o)--MWAK 08:46, 25 November 2006 (UTC)

<<The main point is that Voortle's premise <<"dinosaur" never refers to birds>> is simply false.>> No, it's not false. In pop culture and common usage, "dinosaur" means non-avian Dinosauria. One may argue that the Japanese should be considered Caucasians, because of the "humanness" of both groups, but that doesn't change the fact that the "Caucasian" by definition, does not refer to Japanese people. Similarly, just because some may argue that birds should be considered dinosaurs, does not change the fact that "dinosaur" by definition does not refer to birds. The dinosaurs became extinct 65 million years ago, leaving their decendants (the birds). Voortle 15:44, 25 November 2006 (UTC)

"In pop culture and common usage, "dinosaur" means non-avian Dinosauria" Luckily, the current Wikipedia article is not on pop culture or common vernacular terms in american English. It's about dinosaur science, and the vast, vast majority of dinosaur scientists agree with the phrase "birds are dinosaurs". There are countless sources for this listed throughout the relevant articles.

""dinosaur" by definition" What definition? The phylogenetic definition of Dinosauria is usually either Iguanodon + Megalosaurus or Triceratops + Birds. The apomorphy-based definition usually refers to the perforate acetabulum (a feature shared by dinosaurs and birds). Additionally, the Dinosaur article errs on the side of conservatism and uss a paraphyletic definition anyway! Despite the fact that virtually all modern paleontologists use a cladistic definition of dinosaur that includes birds, the article does not. It's not exactly out of line, therefore, to point this fact out in the present article.Dinoguy2 17:45, 25 November 2006 (UTC)

Also the comparison with the relation between "Caucasians" and "Japanese" is false (beside the dubious anthropology): in this example the Japanese are not the descendants of Caucasians. What Voortle proposes is something akin to saying "Germans aren't Caucasians but the descendants of Caucasians". --MWAK 08:33, 26 November 2006 (UTC)

[edit] Phylogenetic challenge to the coelurosaur hypothesis of bird origins

Kurochkin (2006) published a scientific paper revealing convergent evolution between theropods and birds. He concluded that Archaeopteryx and the enantiornithines descended from a theropod group in the Upper Jurassic, with modern birds and their relatives diverging from an archosaur ancestor in the Upper Triassic. This conclusion was based on the differences in the finger digit homology of birds and theropods. His paper confirms not only that birds aren't really descended from theropods, but also that Protoavis is avian. The cladogram below reveals a different tale about bird relationships:

Archosauromorpha
|--Theropoda
|  |--Coelurosauria
|  `--+--Troodontidae
|     `--+--Alvarezsauridae
|        `--+--Oviraptoridae
|           `--+--Dromaeosauridae
|              `--Sauriurae
|                 |--Vorona
|                 `--+--Archaeornithes
|                    `--Enantiornithes
`--+--Protoavidae
  `--+--Confuciusornithidae
     `--Ornithurae
        |--Zhyraornithidae
        `--+--Liaoningornis
           `--+--Ichthyornithes
              `--+--Hesperornithes
                 `--Neornithes

Why did Kurochkin include Protoavis in his cladistic analysis?

Kurochkin, E.N., 2006. Parallel Evolution of Theropod Dinosaurs and Birds. Entomological Review, Vol. 86, Suppl. 1, pp. S45-S58. —The preceding unsigned comment was added by 72.194.116.63 (talk) 01:52, 10 January 2007 (UTC).

"Revealing" parallel evolution goes a bit far (though it's obviously true prima facie as written here; toothless beaks are indeed an avian-NAT homoplasy... ;-) ). His paper confirms nothing; a cladistic analysis cannot "confirm" anything, only support a hypothesis (cladistics cannot even falsify a hypothesis, scientifically speaking, as it interprets evidence instead of being evidence). As long as his hypothetical protoavian archaeosaur has not been found, nothing is "confirmed"; this paper (in an entomological publication?!) shows the debate is not over but that's all. Whoever treats Protoavis as a biological entity (instead of a hollow shell of a taxon) deserves what he gets IMHO; there is no good case for it being non-chimeric. Of course every cladistic analysis that utilizes the (with almost 100% certainty) archaeosaurian bits assigned to Protoavis and believes it to be avian will yield "proof" that avians are descended from archaeosaurs... the Avicephala don't bear that name without a reason. These should have been included in the analysis. Also, where's the outgroup?

I'd say: forget the conclusions. Barsbold had figured out what was going on 20 years ago, as far as anyone can say now. Him being from Soviet Mongolia, I would not exclude that he meant his statement typologically which is wrong of course, Trofim Lysenko be cursed, but it seems he was very much on the right track: "bird" is a form taxon if not all but restricted to Pygostylia or at least Ornithothoraces, this much is what we can certainly say. It is fairly likely that either Archie or Confuciusornis represents a stem-group divergence from the lineage leading to Neornithes, but maybe neither did; it is near-certain that they didn't both. Try nipping the tree between "Protoavidae" and Confuciusornithodae and rooting in theropods instead; this might actually be close to the real deal. It would at least be a phylogeny that is as good as they get these days.

But the paper does have a definite merit: that Archie is placed closer to the Enantiornithes, and Confuciusornis ("Confie"? ;-) ) closer to Neornithes. While I have reservations about Hesperornithes and would like to see the justification for placing them so high up, the Archie/Confie relationships make my mouth water. "Protoavis" should be thrown out and the dataset combined with May et al's recent paper, and I guess we might be on to something BIG... this is basically Mayr et al's analysis from the bird-end, with a nasty red herring. Dysmorodrepanis 04:50, 10 January 2007 (UTC)

To avoid a possible misunderstanding: Kurochkin didn't perform any cladistic analysis. The "cladogram" was based purely on qualitative judgments of Mr Kurochkin himself, a man who, however, really isn't qualified to judge. Kurochkin never implements correct cladistic methods.--MWAK 09:32, 10 January 2007 (UTC)

Oooh, and I hoped that he had accepted the inevitable at last ;-) What a pity! (I have nothing against cladistics [as a methodology, not as a science branch] - I just don't like it being considered something it isn't, such as "material evidence"; it is a means of reasoning, more akin to dialectics if you will. Case in point: the description of Archaeorhynchus does a cladistic analysis of said taxon which includes a most sweet set of other taxa. Here, Confie goes basal to Enantiornithes, forming a monophyletic clade with them... I think this is the first time I see it. And why not? I am not comfortable with it at all, but it cannot be dismissed; the cladogram again proves nothing BUT it shows that the idea needs further scrutiny before it can be dismissed)

Still, the standards of most cladograms in paleontology are pretty low compared to systematics of extant taxa - hardly you'll see bootstrap values etc, which are essential to interpreting a cladogram. In the Archaeorhynchus paper, Yanornis and Yixianornis do not form a monophyletic clade for example - but with what support me likes to know? They are apparently close, but being stem Ornithurae, "close" can mean anything from "part of a distinct clade" (Yanornithiformes in this case) to "subsequent stem divergences" (which can actually make them de facto closest relatives without being sister taxa in the strict sense - the 2 branches of a dichotomy that is).

Given that the new findings regarding the origin of some human genome sequences suggest that hybridization was continuing for (IIRC) 1.5 MA after the human - chimp split, one wonders whether the dichotomy concept is worth anything at all... if a cladogenesis event takes longer on average than the average time between cladogenesis events, the assumption that dichotomy is a feasible representation for phylogenies even just "more often than not" falls to pieces. (Personally, I prefer to err on the side of caution and remain equivocal about the exact branching pattern around a clade's initical divergence. That recognizable clades exist and can be supported by cladistic methods is fair enough and a lot of undisputable information regarding evolution of lineages can already be drawn from this. Add paleobiogepgraphy and you're set for a lot of insight already; no need to be controversial in many cases actually... And in any case, no matter how limited the fossil record may be - and major radiation seems to involve few major lineages making up 50-95% of the resultant diversity, and the rest consisting of as many "waifs and strays" as needed. This pattern is found over and over again in Neornithes, and I'd guess tit holds true for all theropods at least, in the absence of a megaextinction.) Dysmorodrepanis 16:22, 10 January 2007 (UTC)

Well, perhaps we should see a cladistic analysis as a special kind of dialectics that shows us what is the full content of the material proof. And if we define the date of the split as the last occurrence of hybridisation we solve at least part of the problem. The real issue of course being species variability. ;o)--MWAK 18:14, 10 January 2007 (UTC)

[edit] Good Books on topic

Hi everyone. Im trying to find a good, recent book on the topic of bird evolution and their relationship with Dinosaurs. By recent, i was hoping for something that referred to the feathered dinosaur findings in China.

Anybody know any such books?

As it happens, Luis Chiappe has just published Glorified Dinosaurs: The Origin and Early Evolution of Birds. A must for anyone truly interested in the subject. But it isn't exactly cheap. See: http://www.unswpress.com.au/isbn/0868404136.htm

More technical is his recent Mesozoic Birds: Above the Heads of Dinosaurs, See: http://www.amazon.com/exec/obidos/ASIN/0520200942/qid%3D1028799085/sr%3D11-1 and it is accordingly even more expensive

University of California students may have access to an online version. I recommend this book also as a meta-work, because it represents an earlier stage of the debate. If there is a book starting with which the theropod issue was sorted out for good, it is this. Chiappe's only the editor here; the volume is composed of analyses of paravian taxa from all over the world by many of the great names in the scene. It still is the only comprehensive source for many obscure forms. Dysmorodrepanis 10:34, 6 February 2007 (UTC)

Also Gregory Paul's Dinosaurs of the Air is still a very useful work. As the above link shows, you can order it together with Mesozoic Birds at a reduced price :o).--MWAK 08:34, 6 February 2007 (UTC)