"I had a good discussion with Martin. He's quite a nice guy, it's a shame he's so wrong about almost everything dinobird-related. Seems he officially believes that maniraptorans are birds, but that other coelurosaurs are unrelated. He terms this the "Paulian hypothesis", though it's only similar in thinking of maniraptorans as 2F and preferring the arboreal origin. In his mind, maniraptorans and other birds evolved from a Longisquama-like creature. And like Czerkas believes, some taxa (eg. Scansoriopteryx) are just too hard to place as birds or dinosaurs until a more in depth study is completed. The same old ABSRD arguments were brought up (digit homology, terrestrial theropods, Yixian feathers being collagen, etc.). He referred to both ichthyosaurs and Psittacosaurus as having structures like those found in Sinosauropteryx et al., which is just plain wrong of course. In any case, he does have an interesting eumaniraptoran that will be out soon."
That eumaniraptoran was later named Microraptor gui, btw. As I recall, he said the leg remiges proved M. gui wasn't terrestrial, therefore birds evolved flight from trees, and therefore birds aren't dinosaurs. I then said I have no issue with some dinosaurs being arboreal, which I think he was surprised by.
* Birds Are Not Dinosaurs, contrasted with BAD being Birds Are Dinosaurs
** Maniraptorans Are Not In Actuality Coelurosaurs
I feel Jason's post bends over backwards to seem fair, but also that it leaves out Martin's greatest positive influences on paleontology.
He first writes about Martin being on "our side", which seems to be opposed to creationists, since "He spent his life studying evolution, observing fossils, and we all agreed that dinosaurs and birds were closely related archosaurs." It seems trivially true that anyone will be on your side about some value or opinion. Indeed, even evangelical creationists are on "our side" for wishing to teach people the truth, we just disagree on what that truth is. In any case, as a scientist I think he would have been proud to be against "our side" when it came to heterodox ideas he strongly defended.
Jason believes Martin had a beneficial effect on bird origins research in that BADists "wrote some papers they would not have written unless they felt the need to answer Martin. In the process, progress was made on quantifying the ‘temporal paradox’ issue, and everyone’s hypotheses became more precise and explicit." But I honestly can't think of many examples where Martin's criticisms directly led to science examining the issue more closely to result in more discoveries, they were mostly just pointed out to be based on fallaceous reasoning or inaccurate interpretation. If we look at his classic (1983) arguments for BAND, the temporal gap problem had been answered perfectly years earlier by Ostrom (1976). I don't see Brochu and Norell's (2001) quantification paper as doing more than telling us what we already knew, i.e. the gap between the Tithonian and Aptian is less than between the Tithonian and Triassic. The arboreal vs. terrestrial rationale actually hindered our side in my estimation, as the BAD response was to double down on the terrestriality of Archaeopteryx and flight origins instead of accepting arboreal theropods could exist, which only occured decades later when scansoriopterygids and microraptorians were found. These examples can be contrasted with e.g. Jones et al. (2000) instigating research on Longisquama's parafeathers or Burke and Feduccia (1997) instigating research on digital development.
The next argument is that some recent large morphological analyses (e.g. Livezey and Zusi, 2007) have shown Martin was right that convergent evolution could confound cladistic analyses. I don't think anyone's ever doubted this in principle, as analyses do differ so some must be wrong. Moreover, the ways such analyses were shown to be confounded were never used by Martin (more characters and taxa, molecular analyses, biogeography, etc.), with his naive falsification and evolutionary scenario alternatives ignored (Makovicky and Dyke, 2001). Sure Martin (1997) was right(er) than Chiappe that alvarezsaurids are ornithomimosaurs instead of avialans, but it was for all the wrong reasons, so should that really count scientifically?
Finally, Jason says of Martin's 2005 transition to MANIAC that "I have heard few mention that, in this 2004 paper, Martin rather quietly gave up on that view [that dromaeosaurs were only distantly related to birds]." "... this demonstrates that Martin was open-minded enough to be persuaded by the evidence and to reverse himself on a major part of his hypothesis." While I do give credit to Martin for finally recognizing this relationship, the details make it look less noble. First note Martin never actually admitted his quarter century of arguments against Archaeopteryx and Deinonychus being similar were fallaceous, or that this calls into question his entire methodology. Indeed, he still uses most of them in that very paper, seemingly without realizing his new phylogeny cancels them out (e.g. if maniraptorans are all considered birds, then deriving this whole group from something standard like Ornitholestes eliminates any temporal paradox). Second, he (as with Feduccia) framed neoflightless maniraptorans as a surprising compromise, when by that time most theropod workers considered it possible if less parsimonious. The feeling from MANIAC papers is that taxa like Microraptor and Scansoriopteryx have sent everyone back to the drawing board, when BADists have actually been relatively unaffected besides the character distributions in our cladograms. The impression is an attempt to save face while admitting as little error as possible, which seems distinctly unscientific to me. Still, I'll say Martin's work was less polemical than Olson's or Feduccia's, the latter's 2013 paper being more unhinged than anything Martin wrote.
Well, that's a lot of criticism of a dead man, but I've never been one to follow the tradition of emphasizing the positive aspects of the deceased while downplaying the negatives. Yet positives did exist, and I think his greatest legacies in science have yet to be articulated. Foremost, Larry worked on a LOT besides bird origins. While I'm not qualified to review e.g. his saber-tooth cat work, his hesperornithine work such as the 1976 osteology of Baptornis was quite good. He continued such studies until the end of his life, such as his 2011 ornithuromorph predentary paper with Zhou that analysed an often ignored element. Which brings us to Martin's other great legacy- his students. I know at least Zhou and Witmer trained under Martin. Zhou's been instrumental in expanding our knowledge of Jehol bird diversity. As for Witmer, he has this touching summary on his institutional biography page, which shows my two favorite aspects of his excellent studies are due to Martin-
"I also owe a huge debt to Larry Martin, who got me interested in so many things. He always encouraged me to look at modern animals along side extinct groups, and this has emerged as my major research paradigm, these nascent ideas later evolving into the extant phylogenetic bracket approach. And of course it was Larry who introduced me to the previously under-appreciated anatomical system of cephalic pneumaticity, which became my major research focus for a decade and a half. Although Larry and I are often now pitted as opponents in the fierce debate on avian origins, he has been one of the most important positive influences in my career."
So there are my criticisms and accolades. But there's one more story I'd like to tell. Back in October 2004, I decided to write Larry regarding bird origins. It wasn't meant as a harsh debate, and I wasn't so naive as to think I could do what two decades of published professionals couldn't, but I was intrigued to see where he was coming from and how he would respond to questions and facts that aren't brought up in his papers. Note this was before his 2005 paper declaring his MANIAC status, but I knew he thought that way due to SVP 2002. I reproduce the content of this email exchange below, with changes in color and font between Mickey Mortimer and Larry Martin. I've left out most of the pleasantries preceding and following each actual email, and have formatted them so that e.g. when Martin has four paragraphs, my four paragraphs are responding to them in that order. While publishing email exchanges without explicit permission is of course frowned on in most instances, I'm hoping my own feelings this is ethical once one party is dead are shared by the community. I think of Martin's words being like the personal letters of historical scientists that are now public, and it's all scientific exchange matching what he published as opposed to personal details. So enjoy. I don't think I've ever read a conversation between a BADist and BANDit, which makes this rather unique. For all the criticisms I piled on Larry, I don't know many other scientists who would take the time to write such a long and detailed exchange with an unknown undergraduate amateur. He'll be missed.
I'm an undergraduate at the University of Washington currently investigating theropod and Mesozoic bird phylogeny. I heard you gave a talk the other day where you advanced the hypothesis that maniraptorans are in actuality birds, and that they are unrelated to theropods. I wonder if you could answer a few of my questions. 1. What characters show oviraptorosaurs and dromaeosaurs are birds, while leaving ornithomimosaurs and tyrannosaurs in Theropoda? 2. What is the sister group of birds + Longisquama in your hypothesis? 3. Do you believe homeotic shifts occur in nature? Thank you for your time.
I suppose that we could define birds as animals who have or give evidence of have having an avian wing (primary feathers attached to the middle digit with the palm extending between the middle and outer digits and a digit reduction pattern of 2-3-4) all animals with such a wing may reasonably be supposed to have shared a common volant ancestor. This brings dromaeosaurs and oviraptosaurs into the avian fold. The sister group of birds and Longisquama (including Longisquama relatives) would probably be dinosaurs plus many of the more conventional thecodonts. I am not sure how crocodilians fit in. In any case the connection would be very basal within archosaurs. Please notice that if dromaeosaurs are secondarily terrestrial we can expect many reversals of polarity from earlier analysis. The frameshift hypothesis was badly crunched by developmental types in a recent conferance and is only being maintained to preserve a theropod hypothesis that now fatally flawed.
Accepting your definition of 'bird', why are tyrannosaurs and ornithomimosaurs excluded? We have no embryological evidence to know if they possess digits I-II-III or II-III-IV, and no preserved manual integument that would tell us if they had primary feathers (no manual integument has been reported for Pelecanimimus, Dilong, or tyrannosaurids, though they each preserve integument elsewhere). What characters do dinosaurs and these 'more conventional thecodonts' share than Longisquama and birds lack? Finally, do you mean the particular digital homeotic shift theorized for theropods was questioned in this recent conference, or the reality of homeotic shifts as a whole? In either case, I'd be interested to know the name of the conference, so that I can examine the references. Thanks for the reply. I agree dromaeosaurs and oviraptorosaurs were secondarily flightless, which indeed leads to reversals of character polarity from prior analyses.
Tyrannosaurs are excluded because their hand as restored is not avian, (they are not maniraptoran), maybe evidence could be provided that they were once that way, but why worry until there is some reason. They also lack a lot of the other cranial features, etc. Recent description of so called protofeathers on a tyrannosaurid would seem to be clearly muscle fibers
or ligaments and is probably better seen as evidence for a lack of feathers.
Ornithomimosaurs (including Mononykus) have derived hands with enlarged MTCI and a reduced wrist. I can't see how it relates to the avian hand and think that they are best compared to compsognathids. I think in terms of the general story, it makes very little difference where these taxa go.
If Tyrannosaurs are carnosaurs, we know that at least some carnosaurs have typical dinosaur rosette scale patterns and this may be a dinosaur synapomorphy. They also have interdental plates covered by a
superdentary bone and this would make them very unlikely birds. They also have a long postacetabular ilium, a derived feature found in the earliest dinosaurs and absent from all of the very early birds.
The conference was the Society of Avian Paleontology and Evolution.
Essently none of the developmental types thought much of frameshift although one tried to preserve bird/theropod by postulating a presently
unknown ancestral six fingered hand. You have to ask yourself about
the credibility of an idea that requires a lot of ad hoc new science to keep it alive.
I accept your proposal tyrannosauroids lack some maniraptoran characters. What prevents them from being maniraptoran relatives though? Branching off the bird line before maniraptorans developed all of their distinctive traits? They do share a lot of characters with maniraptorans, after all. Regarding Dilong, what features do its supposed feathers have that would make them less likely to be feathers than the identical structures in Sinornithosaurus' holotype, or the plumulaceous body feathers of Caudipteryx and Protarchaeopteryx (besides the fact you know these last three are maniraptorans; that would be circular reasoning, after all)?
Check out Ingenia for a maniraptoran example of enlarged mcI, though I admit no maniraptoran reduces its carpals like ornithomimosaurs. I agree with you about Mononykus and other alvarezsaurids being closely related to ornithomimosaurs. I even wrote a post to the Dinosaur Mailing List in June about how they were being put inside Maniraptora and Avialae due to flaws of most cladistic analyses. I also agree both groups are close to compsognathids. I think ornithomimosaurs+alvarezsaurids could be very important for your hypothesis, since they show a number of characters you think of as avian- no supradentary; serrationless teeth with basal constriction; large sternum; ossified sternal ribs; costal facets on the sternum; coracoid facets on the sternum; hollow keratinous integument.
Thanks for providing these specific characters. Tyrannosauroids are almost universally agreed to be coelurosaurs now, so we don't have to worry about rosette scale patterns yet. Velociraptor and Dromaeosaurus possess supradentaries, so that can't bar tyrannosauroids from being on the bird line. If we use the ratio between postacetabular and preacetabular processes to be an indicator of postacetabular length, the long postacetabular processes of tyrannosauroids (~120-140%) are comparable to some maniraptorans (Microvenator- 132%; Ingenia- 128%; Sinornithoides- 146%). So that can't bar them from being on the bird line either. Unless you use a different ratio.
I completely agree with the latter sentiment. Unfortunately, the 2004 SAPE abstracts aren't available yet, so I'll have to wait to see what new data was presented. It will be interesting to see how they deal with homeotic shifts observed in human cervical number, which we can validate since we know the geneology of the people in question.
please give citations for superdentaries in maniraptorans of any sort!
I think that the position of tyrannosaurs is quite controversal and it doesn't make any difference to me how they fall out.
I am not convinced that any of the so called protofeathers are real. Everybody has muscles and just because something is on a bird doesn't mean it's a feather. Gladly. If you ever want confirmation of my statements, just ask. Dromaeosaurus- Currie, 1995. New information on the anatomy and relationships of Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal of Vertebrate Paleontology. 15, 576-591. Velociraptor- Barsbold, 1983. Carnivorous dinosaurs from the Cretaceous of Mongolia. Joint Soviet-Mongolian Paleontol. Expedition Trans. 19, 5-120.
If tyrannosauroids are stem-birds, they would help us understand bird evolution a lot. There's a big gap between Longisquama and dromaeosaurs, but tyrannosauroids help fill it out. Besides, if theropods and maniraptorans are so distantly related, it should be easy to tell them apart, right? Even in famous cases of convergence like thylacines vs. canids, Notoryctes vs. talpids or hesperornithines vs. gaviiformes, the differences are easy to see if one looks at skeletal details and not gross resemblence.
This is a very interesting stance I've not seen in the literature. How do you reconcile this with the fact Shuvuuia's hollow cylindrical structures are made of keratin (Schweitzer et al., 1999), and not collagen, actin or myosin?
I doubt that any keratin has survived since the Cretaceous. At least the mollecular types don't buy into Mary's results. Evidence that any of these
structures were hollow is hard to come by. All of the morphological structure
is best expained by other interpretations.
Quite a lot of the anatomy of dinosaurs has been uncertain, for instance the two decade struggle to get the hand and wrist of Deinonychus correctly interpreted.
What are the citations for molecular biologists disputing Schweitzer et al.'s paper, and/or keratin fragments being unable to survive since the Cretaceous? Schweitzer et al. state quite plainly "These fibers are seen to be hollow, both grossly and in microscopic cross section," and photograph an example in figure 2. Which alternative explanation is better for clumps of hollow fibers 200 micrometers in diameter which show smooth outer surfaces, pithy inner surfaces, plate-like structures at one end, small filaments on the outer surface, and consisting of microfilaments of 90-95 nanometers?
Agreed. Even now, there are interesting new possibilities being raised, like Gishlick's (2002) idea maniraptorans' distal carpal III is fused to the base of metacarpal III. As might be expected in e-mail discussions, it seems a couple questions I'm curious about have got lost with all the supradentary and keratin information. Namely- Why are some (which?) 'thecodonts' more closely related to dinosaurs than to Longisquama+birds? Given other examples of tetrapod convergence, shouldn't it be easy to tell maniraptorans from theropods if they are so distantly related?
There has been quite a bit of rethinking of some of the earlier claims and right at the mommentI think that real evidence of intact Tertiary proteins
is pretty cutting edge. Let's say for argumentation that she has keratin tubes,
what feather structure could they be? How would it form? We should have some criteria for thinking something is a feather beyond finding it on a dinosaur if we intend to show that dinosaurs have feathers.
I think that Roger Sawyer who provided the antigens is going to or has commented on the paper.
Alan Feduccia probably could give you more commentary.
Tyrannosaurs are so highly derived that I can't see that they would help much.
Their wrists, hands, ankles. feet and skulls are all more derived and modified
than the other tax we have discussed.
Well, these are only supposed to be keratin fragments, not intact keratin. So that may make it more plausible to you. If they are keratin tubes, the feather structure represented would be the rachis and/or barbs. Prum (1999) goes into detail about how feathers form ontogenetically and perhaps phylogenetically as well. I agree with your statement we need non-circular reasoning if we wish to show dinosaurs have feathers. Prum has defined feathers in relation to the feather follicle, making the first epidermal structure originating from a follicle homologous to those in living birds the first feather. I might just be naive, but it seems to me any epidermal derivitive with a slender cylindrical base necessitates a follicle to grow from. So those of stem-birds (like Confuciusornis and Sinornithosaurus), pterosaurs, and Longisquama are are potential feathers, if we can establish homology with birds' feathers. This latter job is not easy, but is helped by phylogeny and feather morphology. As an example of the former, no non-feathered taxa are closer to modern birds than Confuciusornis or Sinornithosaurus, so their structures are phylogenetically congruent with homology. An example of the latter is the branching observed in the structures of Sinornithosaurus and Dilong, which is unique to feathers.
Thanks. I'll ask them.
This doesn't appear to be true for basal taxa like Dilong. Besides a few characters (symmetrical premaxillary teeth in section; fused nasals; nasals anteriorly convex in transverse section; pneumatic articular; preacetabular notch on ilium), it looks like a good stem-bird. Sure, it probably lacked a true semilunate and other maniraptoran characters, but so did Longisquama.
If I understand Prum's model, his protofeather is none of the above. It does not claim homology with any part of a feather other than the collar
and completely ignores the feather sheath. It was created directly
from the dinosaur protofeathers so there is no surprise that it looks like them.
I certainly don't believe the so called "feathers" in pterosaurs, and I am amazed that nobody seems to to be upset with spreading feathers everywhere especially when the majority of dinosaurs can be shown to be covered with scales.
Why think that these things are feathers when they can't be distinguished from fossilized muscles found in other organisms.
Notice that Mary's study comes from sediments where we might not expect ancient preservation while they > are not duplicated where the opportunity seems better.
Prum's (1999) stage I feather is homologous to the calamus of modern feathers, in the sense that it is formed by an undifferentiated follicle collar. Sorry for not specifying the calamus last time, I was grouping it with the rachis in my mind. Prum and Dyck (2003) describe sheath morphogy and development in detail. Though I can't claim to know Prum's thought processes, Prum and Dyck describe how the model is largely dictated by the developmental mechanisms of feathers (hierarchical modules), not merely resemblence to Sinosauropteryx and Beipiaosaurus feathers. Barbs have to evolve before rachis because the rachis is just a fusion of barb ridges; barbules have to evolve after barbs because they are formed by the differentiation of cell layers in barb ridges; the calamus has to evolve first because the barb ridges are differentiations of the collar that forms the calamus. How do you explain the structure of Longisquama's parafeathers being primitive for feathers if they have a rachis and a barbless vane (as shown by those successive magnifications at SVP 2001), when the rachis forms from fused barb ridges?
Basically every pterosaur worker believes pterosaurs had filamentous integument. Why would you doubt it? I know Feduccia cites Unwin and Bakhurina (1994) as a contrary view, but they specifically noted such integument was present in later papers and online communications. They were merely saying that the supposed Sordes hairs _figured up till that point_ were internal fibers. I personally don't think they are feathers, but that's only because there are so many scaled taxa between pterosaurs and birds. Filamentous integument evolved at least twice anyway (birds, mammals), why not a third time? And given the standard phylogeny, diapsid filamentous integument only shows up twice- pterosaurs and coelurosaurs. Unless you count Longisquama's or Psittacosaurus' structures.
What specimens would these fossilized muscles be in? In any case, they can be distinguished from muscles and collagen (Lingham-Soliar, 2003) in the following ways. 1. Dinosaur feathers are too long to be collagen fibers. Even if one were to hypothesize axial frills on Sinosauropteryx, how do you explain elongate filaments on left and right sides of dorsoventrally preserved animals (NGMC 91; many Confuciusornis; Eoenantiornis)? Elongate filaments on areas not expected to have thick skin or need elongate muscle fibers (skull of Microraptor; middle of Bewipiaosaurus' ulna)? 2. Dinosaur feathers are mostly perpendicular to the body wall (along ulna, shoulders, femur of NGMC 91; head and chest of Microraptor; tail and ilium of Sinosauropteryx), which is compatable with collagen, but not with muscle. 3. Dinosaur feathers are not inside the body wall like the fibers of ichthyosaurs. Ichthyosaurs have a very thick body wall, analogous to cetaceans. But proposing the body wall of theropods extended as far away from the bones as seen in NGMC 91 or Eoenantiornis is preposterous. 4. Dinosaur feathers are hollow, unlike collagen. Even if ichthyosaur fibers look hollow due to mineralization stages (and you doubt Yixian dinosaur feathers based on this), the filaments of Shuvuuia are three dimensional, so cannot be explained in this manner. 5. Dinosaur feathers are suspiciously distributed similar to bird feathers. There are none on the feet or distal snout. Elongate feathers are conveniently on the ulnar side of the lower arm (Beipiaosaurus, NGMC 91) and distal tail (NGMC 91). In particular, if they were muscles, we would expect long tibial fibers on at least some specimens. 6. Dinosaur feathers are sometimes intermixed with vaned feathers, such as on the head of Microraptor. This is fairly indisputable proof that whatever the more simple structures are, they are integument. 7. Dinosaur feathers are made of beta keratin, not collagen, actin or myosin. At least in Shuvuuia's case. 8. Why are Yixian lizards, choristoderes, salamanders and psittacosaurs not covered with these structures? They should have muscles and collagen, after all. How do you explain all of these factors? I admit they could also be homologous to turkey bristles (Sawyer et al., 2003), but the data seem to argue against muscle or collagen.
Specimens from the Djadockhta can preserve keratinous structures, in the form of claw tips (e.g. Citipati in Clark et al., 1999). On the other hand, how many specimens with preserved internal soft tissues have been found there?
The theory that the rachis is fused barb ridges was rejected some decades ago and the problems that it had then still aren't resolved.
Why would you have a calmus if you have nothing else and where does the feather sheath come in?
Does Prum actually say that the protofeather is a calamus. I don't remember his saying so in any presentation. I asked him once what part of a
feather he was talking about, but the collar was all that I got out of it.
You might try Paul Maderson if you want a critque on his model of feather development.
Have you read Harris et al. (2002), which shows barb ridges fusing to form a rachis in figure 4F-J? Indeed, barb ridges can be induced to fuse to form rachis if the follicle is split into two (Prum and Dyck, 2003). Any explanation? Harris MK, Fallon JF, Prum RO. 2002. A Shh-Bmp2 developmental module and the evolutionary origin and diversification of feathers. J Exp Zool (Mol Dev Evol) 294:160-176.
Among the more plausible theories is for insulation (it would be comparable to having fur). Since the sheath is subsumed by the calamus once the latter starts developing, and becomes an indistinguishable part of it, one might assume a feather which is formed completely from the undifferentiated 'calamus setting' of the follicle collar would lack a sheath. Sheaths would have evolved only once the follicle collar became differentiated into barb ridges.
Prum says stage 1 feathers were formed by an undifferentiated follicle collar, which is the same way that modern birds form their calamus. Portions of feathers are only homologous in the sense that homologous genetic patterns are being expressed at the time they are formed. Maderson's model seems to contradict the developmental and genetic evidence in asserting scales and feathers are homologous past the placode stage and that barbs are formed from frayed scale edges. Do you have any explanation for why muscle or collagen would exhibit the eight traits I noted last time in coelurosaur and bird filaments? They're listed below in the copy of that message.
Comparison with dinosaurs should be through the common ancestor of the
maniraptorians and birds which according to the cladograms would have an
avian wing. If anything else is included as closer to maniraptorians
than to birds, it would share that ancestor and hence be uninformative.
If microraptor is a good model the common ancestor would not be bipedal.
Longisquama has many feather features while protofeathers have essently none.
It also has an avian shoulder girdle.
Yes, but tyrannosauroids and ornithomimosaurs would be outside the maniraptoran+birds group, not necessarily have an avian wing (presence of primaries unknown), and thus be informative.
Sure, but the stem leading to that common ancestor could be bipedal. We don't have Longisquama's hindlimbs, after all.
I suppose I'll bite. Like Longisquama's structures and bird feathers, protofeathers are elongate, have a cylindrical base (hence, follicular development), and a hollow shaft (Shuvuuia). Pulp caps and sheaths are not even seen in Yixian bird remiges or retrices, so their apparent absence in protofeathers is meaningless. The vanes of Longisquama's structures consist of a two-layered sheet (since they were filled with sediment; Reisz and Sues, 2001), so are only superficially similar to a feather vane (which forms from barb ridges). I fail to see any feather features parafeathers have that are absent in protofeathers, let alone many. Are there any I missed?
Could you be more specific? Coelurosaurs have slender scapulae and furculae too, so those characters can't be used to place Longisquama closer to birds than coelurosaurs. I can't recall hearing of any other avian pectoral characters in Longisquama.
Why you resist the one that has a lot of evidence for avian structure and support the one that does not is more interesting to me than the debate.
If you want to argue a bipedal ancestor and I would ask why you would even care? Than you must go quadrupedal to bipedal to quadrupedal to bipedal. This seems to be tedious and should only be pushed because of compelling evidence.
If tyrannosaurs should turn out to be another secondarily terrestrial lineage, I don't see how that advances the discussion.
It's exactly the same for me, though of course we have different views regarding which specimens have a lot of evidence for avian structure and which have less. I don't expect to convince you my opinion is correct (since it's been argued many times in the last couple decades by people with far more experience) in this debate. I'm mainly curious why you hold your position and how you justify it. But it's only fair I explain why I resist and support what I do too. In regards to Longisquama, here are the reasons I don't accept it as feathered. Reisz and Sues (2000) have shown the supposed sheath is actually an infilling of sediment. This is proven by the fact that it covers the vane corrugations on both part and counterpart, so must be internal. I have not heard a defense of why this is wrong from you or anyone else who supports a feathered Longisquama. The vane, being formed of two sheets, is unlike a feather vane in everything except its expanded shape. I've heard no developmental hypotheses for changing this into a vane of barbs from you, Maderson or anyone else. The fact it can fold or is expanded distally has no relevence if it isn't homologous. Senter (2003) notes the supposed pulp caps are troughs between corrugations on the middle vane. He also describes the structures as being tripartite, with anterior, middle and posterior vanes (the posterior vane narrows distally until it disappears at midlength, while the middle and anterior vanes expand to form the distal half. I don't have the proper photos to determine if these features are correct, but the fact multiple interpretations exist certainly makes me weary of accepting Jones et al.'s view (especially when the latter has proven incorrect in the ways described above, and in regards to the supposedly separate barbs too- the successively enlarged photos of the vane edge at SVP 2001 were convincing). All this leaves in regards to featherlike characters is the narrow base, which isn't too convincing since protofeathers exhibit it too, and the rest of Longisquama's anatomy places it outside Sauria (Senter, 2003; 2004). I've told you why I support protofeathers, with my eight ways they differ from collagen and/or muscle. Until you tell me why those are incorrect, we can't progress on that topic.
When you said Microraptor was quadrupedal, I assumed you meant while climbing. While on the ground, you think Archaeopteryx and Confuciusornis were bipedal, and since the former is so similar to Microraptor, I assumed you thought it was bipedal on the ground too. So if we are concerned about terretrial locomotion only, birds are always bipedal, which is congruent with ornithomimosaurs or tyrannosauroids being stem birds. While climbing, I don't see why small ornithomimosaurs or tyrannosauroids wouldn't use their hands too. Hell, with more arm/wrist mobility and perhaps no remiges, it might have been easier for them than for maniraptorans.
Here are my thoughts for how it could advance the discussion. Foremost, I'm trying to understand how you justify separating maniraptorans from theropods. I know you'll use the homeotic shift for four-fingered theropods, so I'm concentrating on the tridactyl ones. You suggested postacetabular length and supradentaries, but I showed those characters don't work. It's just such an odd concept to believe theropods and maniraptorans are so distantly related, while being unable to assign some taxa known from many complete skeletons to either group. At least back when you thought maniraptorans were dinosaurs, you had a list of characters that could be used to separate dinosaurs from birds (hypopubic cup; expanded tooth roots; four carpals; etc.). So although you thought the groups were superficially similar, these details could be used to differentiate them. But that doesn't seem to be true for your new view. This confuses me. Secondly, your entire philosophy of 'not caring' about the relationships of tyrannosauroids and ornithomimosaurs is confusing. Finding that maniraptorans are birds warrants a public talk, but what the next most closely related group is seems unimportant to you. There's a huge morphological gap between Longisquama and birds, and you haven't been able to give reasons tyrannosauroids and ornithomimosaurs don't fill that gap. If they are stem birds, it would give us more evidence to use when deciding what the next most closely related group is. And I assume that question is important to you. This is analogous to my confusion regarding why you or any other supporter of feathered Longisquama has never tried to figure out where in Archosauria it goes. The relationships between archosaurs have been well resolved for over a decade, I would think such an important taxon would be worth classifying more precisely.