In the previous article we looked at the Birds Come First, or BCF, hypothesis. It goes without saying that BCF has not won acceptance in the community, nor - in fact - is it even familiar to the majority of archosaur workers. Here, we take a critical view of BCF: does it stand up, or does it fail?
To begin with, let me note that the underlying premise of BCF is fundamentally problematical: the idea that there is some sort of 'central trunk' (Olshevsky 1994, p. 42) or single, unbroken lineage that extended from the first stem-archosaur to the most recently evolved, modern bird. Old 'family tree' diagrams did indeed show a single, central lineage that included the ancestors of the various 'branches' - this is where we get the erroneous idea of ladder-like progression and missing links from - but this concept is erroneous and always relies on the idea that one group or species is somehow special, or sat at the 'top' of the tree (in most trees that 'special' organism is Homo sapiens). It's true that birds represent a highly speciose clade relative to other archosaur groups, and that - relative to the ancestral condition - they are one of the most 'modified' archosaur groups, but they are no more 'central' than any other lineage: they are simply one side-branch among many. It's misleading to imagine that all other archosaurs branch off of the lineage that was destined to lead to birds.
Furthermore, if we indulge in a bit of concestor reconstruction, we see no indication of small, arboreal ancestors at any of the divergence points within non-paravian archosaurs. To take a few examples: the concestor of the coelophysoid + other theropod clade was apparently a small, terrestrial carnivore that resembled Coelophysis, the concestor of the sauropodomorph + theropod clade was a terrestrial, presumably bipedal omnivore that looked something like Thecodontosaurus, and the concestor of the ornithischian + saurischian clade was a bipedal, terrestrial omnivore or carnivore with grasping hands and good cursorial abilities, apparently something like a cross between Eoraptor and Heterodontosaurus. And so on.
Despite this, I think that there are a few aspects of BCF that do have an intuitive appeal. The notion that the gradually accrued, bird-like characters of theropods might have appeared as 'improvements' for an arboreal way of life does seem fairly logical, for example. But, ultimately, BCF is entirely unsatisfactory: we're supposed to construct scientific hypotheses based on the evidence we have, rather than on the evidence we think there should be, and BCF is just way too speculative. It proposes the existence of a whole lineage of hypothetical creatures that are absent from the fossil record.
Where are the dino-birds?
There is, as yet, no evidence that the dino-birds predicted by BCF ever existed. The existence of such creatures is pretty important for the hypothesis: the discovery of a small, arboreal, feathered maniraptoran theropod would not provide obvious support for BCF given that such creatures are entirely compatible with the standard model. Look at the scansoriopterygids, for example: they are deeply nested within the maniraptoran radiation, and do not tell us anything about the animals along the theropod or dinosaurian or archosaurian stem. Conversely, the discovery of a small, arboreal basal ornithischian, or crurotarsan, or stem-archosaur would provide support for BCF, yet the fossils we have so far are entirely consistent with the mainstream view that the ancestral members of most archosaur clades were reasonably large (as in, more than a few kilos at least), terrestrial animals without climbing specialisations.
A few fossils have been suggested to be potential dino-birds, but they're nothing to do with dinosaurs, nor even with archosaurs. Megalancosaurus from the Late Triassic of northern Italy was used as a dino-bird by Olshevsky (1994). It's a weird climbing beast with a prehensile tail, described by Renesto (2000) as having a 'bird-like head on a chameleon body', and it doesn't exhibit any dinosaurian characters: it's part of a very weird group of diapsids (the drepanosaurids) that differ fundamentally from dinosaurs, and indeed from ornithodirans and from most archosaurs, in most aspects of anatomy [adjacent Megalancosaurus reconstruction © Silvio Renesto, from S. Renesto's Vertebrate Paleontology at Insubria University site, used with permission].
Authors have generally considered drepanosaurids to be close to protorosaurs (the archosauromorph clade that includes Tanystropheus and kin; Archosauromorpha is the diapsid clade that includes protorosaurs, rhynchosaurs and archosaurs: for discussion please see the third Tet Zoo rhynchosaur article). However, Senter (2004) proposed that drepanosaurids are rather more basal within Diapsida than this, and that - together with Longisquama and Coelurosauravus - they belong to a new clade (dubbed Avicephala) that is only one step up on the cladogram from Petrolacosaurus and kin, the most basal diapsids. If Senter is right, then drepanosaurids have nothing whatsoever to do with archosaur or archosauromorph evolution.
However, I've always been pretty sceptical of the whole Avicephala thing, mostly because I don't find the evidence linking Longisquama and Coelurosauravus with the drepanosaurids to be convincing. Renesto & Binelli (2006) looked anew at Senter's data set and included lots of new data from additional drepanosaurid specimens. They also included a basal pterosaur. They found a pterosaur + drepanosaurid clade to be within Archosauromorpha, closer to Archosauria than to Protorosauria (pterosaurs are not archosaurs within this phylogeny). Meanwhile, Longisquama and Coelurosauravus remained allied, and in the position that Senter recovered for Avicephala, but nowhere near drepanosaurids [a very simplified version of Renesto & Binelli's cladogram is shown above]. However, even if pterosaurs and drepanosaurids do form a clade, there seems no obvious reason why the features of their common ancestor also applied to the archosaur common ancestor: none of the basal archosaurs or the basal members of the archosaur out-groups (like Prolacerta, protorosaurs and rhynchosaurs) were tiny, climbing animals. Instead, they were mid-sized, terrestrial animals, perhaps able to clamber about in shrubs and whatnot, but without arboreal specialisations (though it's been suggested that some trilophosaurids were scansorial).
Longisquama - famous for its amazing dorsal 'plumes', likened (erroneously) by some to feathers - has also been imagined as a dino-bird, but, as will already be clear, it shouldn't be linked with dinosaurs or even archosaurs. It exhibits no dinosaurian characters, and doesn't even seem to be an archosauromorph, despite thoroughly unconvincing efforts to show that it has an antorbital fenestra and might resemble birds (e.g., James & Pourtless 2009). Cosesaurus [shown here] - a small, quadrupedal reptile from the Triassic of Spain - was also suggested by Olshevsky (1991) to be a potential dino-bird, and spike-like impressions preserved on either side of its tail were even suggested to be proto-feathers. It's now agreed that Cosesaurus is a protorosaur (Peters (2000) interprets it as a close relative of pterosaurs, with both taxa being nested within Protorosauria), and the impressions on the tail are apparently sedimentological artefacts (Ellenberger & Villalta 1974, Ellenberger 1977). As such, Cosesaurus does not have any special relevance for archosaur or dinosaur evolution, and (like other protorosaurs) it lacks any obvious indication of an arboreal lifestyle.
In short, there is no evidence that small, arboreal non-maniraptoran archosaurs might have existed. There are no 'dino-birds'.
Finally, what of the 'three problems'
We saw in the previous article that BCF posits the existence of three problems that supposedly show how the standard hypothesis of archosaur phylogeny is flawed and inferior to BCF. In fact, none of the problems really are problems.
The 'time problem' points to the fact that basal birds (Jurassic archaeopterygids) predate the flightless maniraptorans that are, according to the standard phylogeny, more basal than birds. Ergo, flightless maniraptorans (the mostly Cretaceous dromaeosaurids, oviraptorosaurs and such) are more likely derived from archaeopterygid-like ancestors, rather than vice versa [as shown in the cladogram below. Illustrations by Ken Kirkland (troodontid), Darren Naish (oviraptorosaur) and Greg Paul]. Several observations nullify this contention. Firstly, we construct phylogenetic hypotheses by looking at the distribution of characters: the distribution of taxa within time is effectively irrelevant. It doesn't matter that some maniraptorans are geologically younger than the oldest known birds: phylogenetic analyses that have good sampling across taxa and morphology still show that those maniraptorans are more basal than birds. Secondly, it is dishonest to imply that the absence of some maniraptoran lineages from Jurassic strata is really that meaningful: for reasons that are not well understood, the Jurassic record of small theropods is poor, and the few taxa that are known from good remains generally come from rare lagerstätten deposits. Thirdly, despite this poor Jurassic record, some Jurassic fossils are compatible with standard phylogenies. Eshanosaurus is a possible therizinosauroid from the Early Jurassic (see the comments here for more), and it's no secret that a troodontid is now known from the Morrison Formation, for example. Numerous dromaeosaurid and additional troodontid fossils (admittedly, mostly consisting of teeth) are similar in age to archaeopterygids, showing that deinonychosaurs are at least as old as birds. These discoveries - Eshanosaurus in particular - indicate long ghost lineages for many maniraptoran clades. In other words, there is no 'time problem', just a spotty fossil record.
The 'size problem' asserts that the evolution of small size among proto-bird maniraptorans is, in the standard model, incompatible with Cope's Rule and hence less likely than the alternative (that small size was present ancestrally throughout the history of Archosauria, and that large size is always derived). The fact is that lineages can become miniaturised during evolution, though the reasons for such modifications necessarily remain speculative. Paravians evolved small size (Turner et al. 2007), and it's possible that this has something to do with climbing, with flight, or with something else entirely (like avoiding predation from other theropods, or exploitation of particularly small prey). All of the really small coelurosaurs that are now known (they include the dromaeosaurids Mahakala, Shanag, Rahonavis and Microraptor, the troodontid Jinfengopteryx, the scansoriopterygids, and a few alvarezsaurids and oviraptorosaurs) are maniraptorans, and there is no evidence that small size evolved further down the tree. In short, we simply have to posit that small size really did evolve somewhere within Maniraptora, Cope's Rule or not. In other words, there is no 'size problem', just a single evolutionary event.
Finally, the 'wing problem' argues that the standard model provides no obvious explanation for the evolution of the avian wing, and that the wing most likely evolved in an arboreal setting among dino-birds. The fact that long remiges have now been documented in oviraptorosaurs, dromaeosaurids and other maniraptorans shows that feathered arms essentially the same as those present in basal birds evolved somewhere round about the base of the oviraptorosaur + paravian clade, and there is no evidence that wing-like arms were present in more basal coelurosaurs, nor in other theropods, or other dinosaurs, or other archosaurs. Why did long remiges evolve among maniraptorans? We don't know. One proposal is that enlarged remiges helped small maniraptorans to propel themselves up steep inclines and tree trunks: so called flap-running, or wing-assisted incline running, or WAIR (Bundle & Dial 2003, Dial 2003a, b, Dial et al. 2008) [adjacent image shows WAIR in action. Even 'half a wing' is indeed useful]. Fact is, recent discoveries have shown that the avian wing is really nothing special compared to the forelimb morphology present elsewhere in Maniraptora, and the 'wing problem' wrongly assumes that it is. Ergo, there is no 'wing problem'.
Wrapping it all up
BCF is a very interesting hypothesis, not least of all because it proposes the existence of numerous small, climbing archosaurs - those 'dino-birds' - that sound fun and interesting. But it fails on many levels. (1) It assumes that all of the bird-like characters that accrued during archosaur evolution accrued because the clade as a whole was heading toward increasing birdiness, but this is only true if you imagine to start with that birds have a special place on the cladogram. There's no reason to think that this is true. (2) It assumes that the concestors all the way along the archosaur cladogram were small, bird-like, arboreal animals, yet there is no evidence for this, and outgroup comparison always refutes it (except, notably, within Maniraptora). (3) It posits the existence of numerous hypothetical ancestral 'dino-bird' forms, yet these remain hypothetical and all purported 'dino-birds' have turned out to be something else. (4) It states that the evolution of small size and evolution of wings within proto-birds, and the stratigraphical distribution of maniraptorans, are unexplained by conventional phylogenies, yet they are clearly not problematical.
For previous articles on non-standard phylogenetic hypotheses see...
- Goodbye from the stem-haematotherm, goodbye from me
- Aquatic proto-people and the
theoryhypothesis of initial bipedalism - Amphisbaenians and the origins of mammals
And for previous articles relevant to early birds and avian origins see...
- Feathers and filaments of non-avian dinosaurs, part I
- Feathers and filaments of dinosaurs, part II
- Long and Schouten's Feathered Dinosaurs, a review
- Tet Zoo picture of the day # 24 (on archaeopterygids)
- A stunning new Mesozoic bird... well, new-ish
- A quick history of tree-climbing dinosaurs
- Epidexipteryx: bizarre little strap-feathered maniraptoran
- A month in dinosaurs (and pterosaurs): 1, therizinosauroid fuzz
- A month in dinosaurs (and pterosaurs): 2, of alvarezsaurids and avialians
Refs - -
Bundle, M. W. & Dial, K. P. 2003. Mechanics of wing-assisted incline running (WAIR). The Journal of Experimental Biology 206, 4553-4564.
Dial, K. P. 2003a. Wing-assisted incline running and the evolution of flight. Science 299, 402-404.
- . 2003b. Evolution of avian locomotion: correlates of flight style, locomotor modules, nesting biology, body size development, and the origin of flapping flight. The Auk 120, 941-952.
- ., Jackson, B. E. & Segre, P. 2008. A fundamental avian wing-stroke provides a new perspective on the evolution of flight. Nature 451, 985-989.
Ellenberger, P. 1977. Quelques precisions sur l'anatomie et la place systematique tres speciale de Cosesaurus aviceps. Cuadernos GeologÃa Ibérica 4, 169-188.
- . & de Villalta, J. F. 1974. Sur la présence d'un ancètre probable des oiseaux dans le Muschelkalk supérieur de Catalogne (Espagne). Note préliminaire. Acta Geológica Hispánica 9, 162-168.
James, F. C. & Pourtless, J. A. 2009. Cladistics and the origins of birds: a review and two new analyses. Ornithological Monographs 66, 1-78.
Olshevsky, G. 1991. A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Publications Requiring Research, San Diego.
- . 1994. The birds first? A theory to fit the facts. Omni 16 (9), 34-86.
Peters, D. 2000. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106, 293-336.
Renesto, S. 2000. Bird-like head on a chameleon body: new specimens of the enigmatic diapsid reptile Megalancosaurus from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 106, 157-180.
- . & Binelli, G. 2006. Vallesaurus cenensis Wild, 1991, a drepanosaurid (Reptilia, Diapsida) from the Late Triassic of northern Italy. Rivista Italiana di Paleontologia e Stratigrafia 112, 77-94.
Senter, P. 2004. Phylogeny of Drepanosauridae (Reptilia: Diapsida). Journal of Systematic Palaeontology 2, 257-268.
Turner, A. H., Pol, D., Clarke, J. A., Erickson, G. M. & Norell, M. A. 2007. A basal dromaeosaurid and size evolution preceding avian flight. Science 317, 1378-1381.
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More like this
By some strange coincidence, research just published seems to support this BCF hypothesis: Discovery raises new doubts about dinosaur bird links.
"We aren't suggesting that dinosaurs and birds may not have had a common ancestor somewhere in the distant past," Quick said. "That's quite possible and is routinely found in evolution. It just seems pretty clear now that birds were evolving all along on their own and did not descend directly from the theropod dinosaurs, which lived many millions of years later."
Excellent work - thanks for the post.
@1: Gostone: see Darren's comment Number 68 in the First Part.
Pterosaur origin is a very interesting topic.
It's one of the few areas of reptile palaeontology where Italy gives a very good fossil contribution (basalmost pterosaurs, protorosaurids and drepanosaurids). :-)
Could you supply some details? How many known trilophosaurids are there even?
Thanks for comments. David, see...
Spielmann, J. A., Heckert, A. B. & Lucas, S. G. 2005. The Late Triassic archosauromorph Trilophosaurus as an arboreal climber. Rivista Italiana di Paleontologia e Stratigrafia 111, 395-412.
I might do an article on trilophosaurids some time, no time to elaborate right now.
Wow. Wasn't Trilophosaurus 3 m long when adult?
@original post, isn't this like shooting fish in a barrel? ;)
David, big iguanas (like ~2 m+) still can climb trees.
It's kind of odd that Olshevsky considers arboreality the defining characteristic of "birds", when it doesn't even seem to be plesiomorphic for crown-group birds! (I imagine the ancestral avian [i.e., the final common ancestor of the crown group] to look something like a tinamou or grouse.)
As I've discussed many times, I don't think "bird" can be defined -- it's a vernacular word, so it means whatever it means. But, for the sake of argument, let's consider a definition that has been advanced by some people: a "bird" is a "feathered animal". In that case, depending on how loosely you define "feather", "birds" may well have come first! Tianyulong and Psittacosaurus suggest that filamentous integumentary structures may have been plesiomorphic for Dinosauria. If homologous with pterosaur "fur", these structures would even be basal to Ornithodira (which, depending on the position of pterosauromorphs, might include crocodylians!).
Thus we may well have a lineage of "fuzzy" ancestors leading up to birds and spitting off various scaly groups (thyreophorans/eurypods, ornithopods/hadrosaurids, sauropodomorphs/titanosaurs, ceratosaurs/carnotaurines, carnosaurs/Allosaurus, etc. -- each of those pairs a maximally inclusive and a minimally inclusive clade for the trait of featherlessness). However the "fuzzy" group is not a trunk, but a massively paraphyletic assemblage -- i.e., the "avian trunk" also "spit off" plenty of feathered/fuzzy lineages. Also, there's nothing to suggest any of these fuzzies (or, if you want, "birds") were arboreal.
(A very similar situation notably exists in mammals.)
@Gastone, the U of Oregon study seems riddled with misunderstandings about basic theropod anatomy and evolutionary developments along to the avian clade. "A velociraptor didn't just sprout wings and fly away"...what the hell?!? It seems like they used the data to fit their preconceived notions of avian ancestry. I still find it so interesting why non-paleontologists find the dinosaurian ancestry of birds so hard to swallow. I think Darren's nod to the favored exceptionalism of birds over other vertebrates for these folks clouds their science.
Darren, this is one of the best examinations of the BCF that I've ever read. I thought the debate was long dead, but it seems like some people just won't give up the ghost. Thanks for laying it all out there. The burden of evidence is still on them, no matter how many studies on modern birds with "conclusive proof" that birds are not dinosaurs they manage to come up with. I will believe it when I see the fossil evidence!
I'm not sure I understand point (1). The phylogenetic tree has all kinds of "central trunks" in it, doesn't it? I don't see how central trunkiness is an argument against BCF; I mean, obviously it isn't an argument *for* BCF, but I don't see why you would discount a theory *because* it posits a "central trunk."
Great fallow-up, Darren! By the way, what do you think of John Ruben and the BAND's latest claim that (just like all those others they came up with) sopposedly defies the notion of dinosaur-to-bird evolution? If you haven't seen it yet, Gostone provides a link in his comment.
Never mind Darren, I saw your resonse to the claim over on the first article just a second ago. The BAND will stop at nothing to "prove" their wacky ideas, will they?!
Someone needs to give those guys from OSU a good talking to about how to not look like cranks. Number 1: At the end of your article don't imply paleontologists are persecuting your idea.
Ech,
Here's the problem. The "central trunk" idea suggests a evolution towards birds to justify calling everything along the trunk "birds" (which includes common ancestors of everything). "Birds" came first would therefore be true by definition alone.
An analogy would be to say there was a central trunk leading to Homo sapiens and defining every organism which was ancestral to present day Homo sapiens as "human". That however would include the common ancestor of every living organism! So of course "humans" came first, but in this case the ancestral "human" could be some microbe.
Noadi: As an OSU alumnus, I feel obliged to take exception to your aspersion. The UofO and everybody in it are tens of miles away from OSU. Crankiness isn't an essentially Oregonian character, it arises sporadically in different places irrespective of state boundaries. (The Texas problem is probably just a matter of size; throw a dart at the lower 48 and you're likely to hit Texas.)
The thought occurred to me that I have been treating BCF as equivalent to BAND (BCF=BAND). Is that necessarily true or are both sets of ideas represented by different (groups of) researchers? If they are different, what criteria are used to distinguish them? Just curious!
I think BCF is more of a subcategory of BAND.
It's in fact necessarily wrong. :-) The only things they have in common are: 1) they both assume an arboreal origin for birds and their flight; 2) they both consider the "avicephalans" important to the origin of birds and their flight; 3) they're both manifestly wrong. Under BCF, birds are dinosaurs as usual, except that Olshevsky has a nomenclatural preference for using all vernacular names for clades for their total group (so that all dinosauromorphs are birds).
Did anyone else scroll down to that Megalancosaurus pic and at first think it was a satirical image of a tiny sauropod in a tree?
Chris Noto wrote:
No, BCF is a goofy offshoot of the "standard model" where birds are nested well within theropod dinosaurs. The differences arise in the application of the term "bird" to the "central trunk" leading to real birds; assuming that all these MRCAs were small, arboreal, and never fossilized; and claiming that some organisms that were clearly well outside of Ornithodira are really early fossil birds sensu Olshevsky.
It's like the aquatic ape of dinosaurs: both the "standard model" and the alternative use the same phylogenies, but the alternative speculates a lot about behaviors and character states of unfossilized MRCAs.
I just wanted to add a curious note related to Nick's post way earlier (#7) about large iguanas being arboreal that leads to one of my all-time favorite facts - goats can climb trees!
http://www.youtube.com/watch?v=oQev3UoGp2M
In stead of berating George Olshevsky why not email him and, I know this is a wild and weird thought, ask him about it!!!
What the hell?
And for those of you out there I was in fact the first one to come up with the idea. George and I just visted Texas Tech to check out Protoavis. Unfortunatly Sanker wasn't there but Brian Small was and he showed us the picture/illustrations of it. On the drive home I jokeinly said hey, what if it wasn't dinosaurs that came first, but Birds came first. So, you can blame me for the term BCF if you want...
But talking to George and not belittleing his theory is a good idea, which I thought some on this list knew better.
Tracy
I was almost wondering if you were recycling some April 1 posts. This BCF appears to be something that could find its place is close to your rhinogradentians and such other hilarious posts. Only on seeing this post did I realize that you were serious about this specter and were falsifying this in earnest. It is interesting that this borderline idea generates such heat.
Tracy: Can you answer David's assertion that there is no actual content to the notion, but only a naming preference? I.e., in precisely which details can I distinguish it from a naming preference, vs. a generic hypothesis that theropods (or something) started small and scansorial?
I'm not sure I'd want to dismiss the "time problem" quite that quickly: in principle, looking at traits and ignoring their time of appearance in different lineages could, it seems to me, be misleading. Example: Fruitafossor has reduced, peg-like, teeth and (i.i.r.c.) something resembling xenarthrous connections between vertebrae: its discoverers, however, emphasized (saying it about three times in a short article) that they did NOT think it was connected with armadillos. I think they were clearly right to believe that the shared derived characters of F. and extant Xenarthra were convergent, and the main reason why it was right for them to think this, I'd like to suggest, is precisely that F. is WAY too early to be connected to X. (Though there are, of course, other, non-chronological, traits of Fruitafossor that point the same way.) Second example: see Toby White's discussion (on Palaeos.com) of Crocodiliformimorph (or whatever) phylogeny: repeated invasions of marine habitats led to massive homoplasy; one clue to this is simply the chronology of when different "marine crocodile" lineages appear in the fossil record.
Summarizing: SOMETIMES the time problem is something relevant to phylogenetic inference. If similar traits appear in different lineages at wildly different times, THIS ITSELF is evidence that convergence is at work. And probability of convergence is certainly relevant to deciding how much faith to put in a cladogram derived from a traitr matrix.
All of which is consistent with thinking Darren is right, however, in judging that IN THE PARTICULAR CASE of birds and flightless maniraptorans, the time problem shouldn't lead one to reject the standard phylogeny.
(Tracy Ford: Assuming you know George Olshevsky, could you make sure he knows about these posts? My guess is that Darren would welcome his feedback.)
Eh, I'm no supporter of BCF, but I think you could have done a better job countering the 'three problems' here.
To use "Eshanosaurus in particular" as an argument against the time problem is troublesome, as 1) it's possibly sauropodomorph, especially considering the later Falcarius lacks some of its therizinosaur characters, and 2) many paleontologists think the time problem itself indicates Eshanosaurus isn't a coelurosaur. And as Allen says, chronology can indicate problems with a cladogram, even though we don't use it as a character normally. Chatterjee's Protoavis cladograms are in part problematic because of the huge ghost lineages they imply. The main point to make is that deinonychosaurs only have to be as old as birds, not older than them, and that the Morrison troodontid and plenty of dromaeosaurid and troodontid teeth are just as old. Also that Brochu and Norell (2001) found the temporal incongruence to be greater or similar if birds are descended from various non-dinosaur archosaurs.
As for the size problem, there have been studies disproving Cope's Rule, correct? Citing Turner et al.'s paper doesn't help the cause, since their illustrated cladogram has paravians starting out bird-sized and getting larger in various lineages through time. It'd be better to cite Smith et al. (2007), that shows large basal tetanurines, neotheropods, etc..
Hey, Darren, thanks for publicizing BCF. Your "refutation," alas, is way too weak for me. But I'd have to go through your lengthy note literally line by line to show where you've gone wrong, and I don't have the time to do that right now. I've been through your counterarguments myself, many years ago, and figured out why they don't hold water (for starters, don't forget that massive convergence is responsible for much of dinosaur bipedality, all because, as in all known secondarily flightless birds, the forelimbs had become too strongly modifed for flight to return to a terrestrial-locomtion function; this has totally subverted interpretations of all the standard cladograms). Nice try, but BCF still hangs together. Best, G.O.
My science Kung Fu is superior!
@George Olshevsky: You don't offer any arguments against Darren's confirmation, so not only BCF doesn't hold together, its more than disproved unless obvious arguments are given against. Otherwise, its like the creationist game: just hiding away and not providing answers
Fruitafossor is an interesting case because, as the authors mention, the earliest, least well calibrated molecular dating studies did in fact allow for Jurassic xenarthrans. So, the time problem was not a good argument at that time (before it was found out that you can't possibly use a single calibration point to date a large tree, let alone if that tree is full of long-branch attraction as that by Kumar & Hedges 1998 is).
So the authors had to rely on anatomy alone. And they did: they plugged Fruitafossor into a published dataset for mammal phylogeny and ran a cladistic analysis. Lo & behold, Fruitafossor came out near the origin of the mammalian crown-group, very far from the xenarthrans. Take-home message: to show that F. is nowhere near Xenarthra, you can completely ignore the time problem; cladistics alone â the stuff you hide between parentheses â is enough. :-)
Yes, but it takes phylogenetic analysis to show that this clue is actually pointing in the right direction.
After all, it's not like you could simply read the phylogeny of that clade from the first-appearance dates of its members. The discovery of the Early Jurassic goniopholidid Calsoyasuchus unveiled major ghost lineages for at least two clades of freshwater crocodiles â those that are expected to leave at least their teeth abundantly in the fossil record, especially considering that goniopholidid teeth, with their unserrated cutting edges, are hard to confuse with anything.
But again, that's just a red flag, nothing more. The real problems lie in the small taxon sample, the tiny character sample, the miscodings, and the chimeric nature of Protoavis.
Only in particular cases, of course. While it's getting less and less parsimonious, you could still say "yeah, these are all just exceptions", not to mention the cowardish cop-out "it's a rule, not a law".
Till you'll take that time, BCF is best regarded as utterly unnecessary and almost certainly wrong. Take your time, we can wait â but do it. You can't expect us to accept arguments you haven't even told us.
In the meantime, I have a couple of questions for you. For example, why would an arboreal animal ever lose the ability to sprawl its hindlegs, as all dinosauromorphs have done? Some of the most heavily climbing birds have even got that ability back (â¦how are those reed-nesting European passerines called again) because it's so useful for climbing.
I should have mentioned this before, but those of you who have not already seen it, I'd like to draw your attention to me Brachiosaurs Came First model. Details on the DML archive at http://dml.cmnh.org/2007Sep/msg00374.html
But talking to George and not belittleing his theory is a good idea, which I thought some on this list knew better.
Right, because once an idea is out there it's completely unfair to criticize the idea on its merits, we always have to converse directly with the person who generated it. I guess that since I can't get in touch with Darwin to have a critical discussion, I'll just have to accept that pangenes are real, too.
Also, talking to George didn't clear up anything, since he refused to address any evidence and simply declared by fiat that BCF hangs together. Rational argument FAIL.
What falsifies the BADD theory, whose major scenario is the assembly of a flying bird from components that evolved entirely in a terrestrial, nonvolant context, is the sheer unlikelihood of this sequence of events. It is like shaking the box and having all the pieces fall randomly into a perfectly completed jigsaw puzzle. In BCF, the modern bird assembles itself part by part, each new part being an incremental improvement to an arboreal and, later, volant lifestyle. Innumerable species fall by the wayside, to either evolve into various other archosaur clades or, much more frequently, simply to become extinct. What, exactly, about this picture is unreasonable? You can fit any of your favorite cladograms to it, to show, for example, the order in which the various avian novelties appeared. As far as I'm concerned, BCF neatly solves the problem of avian evolution; all that's necessary is to fill in the details.
This really doesn't have much to do with BCF itself, but I'm not sure were else to say it. Anyway, here it goes..
Why is it that palaeontology does not use the Linnaean system anymore? When cladistics began being used, the Linnaean system was totally thown out. This is unlike other fields, such as (modern animal) biology, where the old Linnaean ranks (Kingdom, Phylum, Class, Order, etc.) are used in addition to cladistics. Why use cladistics, a method of figuring out evolutionary relationships, as a taxonomic system? Also, I'm not too sure what's so great about cladistics anyway. They may sometimes be quite useful, but they also sometimes make gross errors. For example, Therizinosaurs wre usually returned in analyses as close realatives of Oviraptorosaurs. But now we have a new Beipiaosaurus specimen that shows only protofeathers, not the true vaned feathers of Oviraptorosaurs. Therefore, Therizinosaurs are far more primitive than Oviraptorosaurs, too much so for them to be closely related. What other goofs could cladistics be making? Also, cladistics often defy common sense, placing animals that don't look anything like each other (Pachycephalosaurs and Cerotopsians, for example) in the same clade. But all that aside, I just want to know what's wrong with the Linnaean system. If we're going to use cladistics, shouldn't grade still be just as important as clade?
(Note: Please exuse any non-italicized bnomial names; I'm not sure how to do them like that on here.)
Mihael Erickson wrote:
"For example, Therizinosaurs wre usually returned in analyses as close realatives of Oviraptorosaurs. But now we have a new Beipiaosaurus specimen that shows only protofeathers, not the true vaned feathers of Oviraptorosaurs. Therefore, Therizinosaurs are far more primitive than Oviraptorosaurs, too much so for them to be closely related."
Can you exclude the possibility that the morphology of Beipiaosaurus' feathers are secondary? In other words, is it possible that that the feathers of Beipiaosaurus evolved from 'true vaned feathers'?
Look at the feathers of a ratite, such as an ostrich or an emu. Or look at the feathers of a penguin. These feathers lack the complex, closed vaned structure seen in the flight feathers of other birds. Yet, we know the feathers of ratites and penguins evolved from the more complex vaned feathers seen in flying birds. So why couldn't there have been a similar reversal in non-avian theropods?
In short: I wouldn't be so quick to dismiss cladistics.
Michael Erickson wrote:
There's a lot I could say about this, but I don't feel like being the one responsible for opening that can of worms (again). Rather, I'll say that I agree with your sentiment, and IMHO, grades/ranks are incredibly useful for what they are designed to do (namely, letting researchers talk about specific groups, and to get concept across without being bogged down in the nomenclature).
Lastly, do keep in mind that it is vertebrate paleontology, and dinosaur paleontology in particular, that has wholly adopted phylogenetic/cladistic nomenclature. Rankless taxonomy gets less common the further from dinos one gets.
To address your other issue: "What's wrong with the Linnaean system?" Linnaean taxonomy is impractical and misleading. It's not just dinosaur researchers who have effectively abandoned it. Many "modern animal biologists" have also abandoned it. In invertebrate zoology, the concept of "phylum" is disappearing as many "phyla" are found to belong to other "phyla".
Ther basic problem is that these ranks (Phylum, Class, Order...) are largely meaningless. It's relative position that's important, not "rank". When "Classes" such as Aves or Mammalia are found to be subsets of another "Class" (Reptilia), it makes no sense to retain Aves, Mammalia and Reptilia as equally ranked groups. Linnaean perceived mammals and birds to be superior to the lowly reptiles. We now know this concept is erroneous and misleading. For this and other reasons it's better just to do away with Linnean ranks altogether.
Last but not least:
"Also, cladistics often defy common sense, placing animals that don't look anything like each other (Pachycephalosaurs and Cerotopsians, for example) in the same clade."
Who says pachycephalosaurians and ceratopsians don't look alike? Look at the skulls!
Also, there's a basal ceratopsian (discovered fairly recently) called _Yinlong_ that reinforces the link between pachycephalosaurians and ceratopsians.
T. Williams, Jura: Thank you all for commenting on what I said. You have convinced me that I was wrong, and you made some VERY good points. For starters, I never really thought about Beipiaosaurus' profeathers being a secondary condition. It actually sounds pretty likely. Thanks for pointing that out. And you know, now that I think on it, Linnaean taxonomy IS impractical! Cladistics may be wrong SOMETIMES (although my examples of this were bogous), but linnaean taxonomy is wrong MUCH more often. Like the separation of birds from reptiles. And It's got that whole "ladder of progress" aoura around it. Mammals and birds superior to reptiles? Bull. Most of the time I think my pet gecko is WAY smarter than my cats. I have also taken a better look at the skulls of Pachycephalosaurs and Ceratopsians, and they DO look alike! (Why the heck did I even say that they didn't? Maybe I was just thinking about basic body structure.) I also took a good look at a skeletal drawing of Yinlong (an animal that I'd heard about but never really looked at) and that sucker looks just like a Pachycephalosaur! I know it sounds cliche, but thank you for showing me the eror(s)of my ways. Oh, and next time I'll think and do more research before I open my big fat mouth. Once again Thanks!
That's ERROR. Sorry.
Hehe, no problem Michael. :-) I wrote these responses in a hurry (I was multitasking at the time), so they were a bit rushed. So any 'terseness' in the tone was accidental and unintentional.
Yep, geckos are pretty smart.
Thanks! I sensed no terseness.
1) It's not a theory, it's a hypothesis, because it's way too small for a theory. A theory is something big and overarching, like that of evolution.
2) How did you calculate that probability?
What's so unlikely about feathers evolving for insulation (and before that maybe as spines or for sexual-selection purposes), then wings evolving for brooding or again by sexual selection, the already present predatory function of the forelimbs and thus their musculature being enhanced in the meantime, and then flight evolving one way or another? Aerodynamic effects are noticeable -- and that also means noticeable for natural selection -- as soon as the wings are big enough to carry 1/4 of the body weight.
Why didn't you answer my question about why an arboreal animal would ever lose the ability to sprawl its hindlegs?
==============
You can use HTML. In this case that means writing <i> in front of the text to be italicized and </i> behind it.
BTW, I bet your browser has auto-fill-in. If you switch it on, you won't need to type your name in every time anymore.
That's a coincidence due to the fact that cladistics and phylogenetic nomenclature were introduced to dinosaur palaeontology at the same time, in the same seminal publications like Gauthier 1986. You can have one without the other.
Nobody does that -- it's not even possible in principle.
It is the method of the science of phylogenetics.
The traditional approaches are:
- pure guesswork;
- cladistics with 1 to 3 characters, which are used to develop a scenario of evolution, to which all other evidence (all other characters) is then fitted rather than the other way around;
- trying to see the phylogeny in the fossil record itself, going by overall similarity and order of stratigraphic appearance. Sometimes combined with the above approaches.
If you read conodont papers, you'll come across stratophenetics, which is the latter approach quantified and thus made objective and repeatable. Problem is, it rests on assumptions about the quality of the fossil record which it doesn't test. In some cases they've been shown to be wrong -- and that's for conodonts, not for something with as spotty a fossil record as dinosaurs!
Well, sure. It's only science. It's not divine revelation or something.
See? That's "cladistics with one character", which amounts to the untested assumption that some characters are "reliable" = immune to convergence.
Funnily enough, however, you're right for the wrong reason. The biggest cladistic analysis of coelurosaur analysis so far, presented last SVP meeting by Lindsay Zanno, finds the segnosaurs as the sister-group of a clade that consists of the oviraptorosaurs on one hand and the eumaniraptorans on the other. The segnosaurs and the oviraptorosaurs are still very close together, but not sister-groups anymore.
What helps against mistakes of cladistics? More cladistics.
That's a pretty clear case of uninformed common sense being wrong, and science showing it to be so. :-)
It makes people believe that they can estimate biodiversity by counting genera, families or orders, even though such entities are not countable.
Sure, all proponents of rank-based nomenclature know full well that the ranks aren't defined and don't really exist in nature -- as long as they consciously think about it. Then they proceed to temporarily forget it. There's a paper by Michael Benton (2007, Acta Pal. Pol.) where he manages to contradict himself in the same sentence in the abstract on whether ranks exist, and then goes on to claim that Carnivora was divided into families based on phenetic analyses that have in fact never been done.
There are ways of really quantifying biodiversity, most notably the Phylogenetic Diversity Index by Daniel Faith (1992, 1994).
I don't think so. Nothing in biology makes sense except in the light of evolution, and nothing in evolution makes sense without a good phylogeny. Tree-thinking.
More importantly, however, rank-based nomenclature only allows you to name some grades but not others. Sometimes it's useful to talk about egg-laying amniotes, for example. No way to give that grade a name without gravely disrupting all existing tetrapod classifications.
In phylogenetic nomenclature, you can give such groups informal names all you want, because there is no classification to disrupt, and even define those names precisely. All you can't do is make such names official.
Nothing cladistic about it.
Sure, phylogenetic nomenclature and cladistics go well together, because PN requires phylogenetic hypotheses to be applied to, and cladistics provides well-tested ones. But you can apply PN (including the PhyloCode!) to phylogenetic hypotheses you just dreamt up, and you can go to the traditional trouble of translating a cladogram into a classification. Nothing stops you.
To be fair, that's not even comparable: rank-based nomenclature doesn't have a method, while cladistics is a method.
T. Williams:
How, exactly, is it impractical? Please explain.
Huh? A rank is something relative! For example: in the Linnaean system, 'Family' is a higher category than 'Genus' but a lower category than 'Order'. (Or to take another example: in military hierachy - surely the ultimate ranked system! - 'Colonel' is higher than 'Major' but lower than 'General'.)
@33:
"In BCF, the modern bird assembles itself part by part, each new part being an incremental improvement to an arboreal and, later, volant lifestyle."
Pardon me, but I do believe your teleology is showing.
David Marjanovic: That's exactly what I meant - Linnaean taxonomy has no method, therefore, it's wrong half the time. Cladistics makes mistakes too, and, as you said, more cladistics is what fixes it.(Please ignore what I had said about cladistics being garbage; I have changed my tune with more thought and research.) As I said, I should have thought on it more before opening my big fat mouth. Thanks for responding to what I had said.
Oh, and thanks for the heads-up on how to italisize those names!
George, please don't use the jigsaw analogy. It's what Creationists and ID'ers use to downplay evolution. We don't need any self-respecting scientists using the jigsaw analogy. The piece-by-piece model is perfectly obtainable in a dinosaurian ancestor. Feathers are the first step, followed by, perhaps, WAIR, then arboreal adaptations from there. Saying that it's silly to think that an arboreal animal evolved from a terrestrial ancestor is not an argument. Terrestrial animals evolved from marine animals. And what's more, that early tetrapod's landlubbing adaptations seem to have first APPEARED in a marine context. And your hypothetical arboreal archosaurs evolved from terrestrial ancestors, too.
I suppose I don't understand why you're keeping dinosaurs "grounded." If you simply don't believe that theropods could EVER do anything other than run around on the ground, then I suppose that necessarily limits your ideas about avian ancestry. But drepanosaurs didn't evolve in a vaccum, and neither did theropods.
And what's at stake here? Why is it so awful to think that birds evolved from theropod dinosaurs? Why is that idea somehow less attractive than if birds evolved from some unknown ghost lineage?
German proverb: "If you don't ask, you stay stupid."
BCF does say that birds are theropods, apart from the fact that it comes with a nomenclatural preference that runs the other way around. What's new is that it rejects parsimony for certain characters and instead states that everything from at least the first ornithodiran to the first crown-group bird was arboreal.
Regarding the term "birds," or Ornithes (as I've called them elsewhere), I simply define this group to be the stem group that contains all vertebrates more closely related to [pick your favorite extant bird here] than to [pick your favorite extant crocodylian here]. This group includes all the dinosaurs, such as sauropods and stegosaurs, which can be visualized as giant, quadrupedal, long-tailed birds. Not my idea but Peter Ax's (1989), and it makes the most taxonomic sense, in that we don't create any kind of arbitrary bird-nonbird demarcation within Theropoda.
George: OK, that's just terminology, or, as others said, nomenclature, and of exactly zero interest -- or even a net distraction -- scientifically. What's left is the assumption of arboreality, and raises the question, then, of what it was that made the transition from the ground to the trees, and whatever happened to all the other co-eval taxa that didn't bother with arboreality.
George, using that logic, we could just call all sauropsids "birds" if we're going to define an entire enormous group by their "most derived" member. There's just as much distance between my geckos and crocodiles as there is between crocodiles and eagles. Probably less.
David Marjanovic: Thanks for making me feel better about asking stupid stuff!
Tracy: Can you answer David's assertion that there is no actual content to the notion, but only a naming preference? I.e., in precisely which details can I distinguish it from a naming preference, vs. a generic hypothesis that theropods (or something) started small and scansorial?<<
No, because I haven't a clue what your talking about. Maybe George would.
(Tracy Ford: Assuming you know George Olshevsky, could you make sure he knows about these posts? My guess is that Darren would welcome his feedback.)<<
Consider it done. But right now he's busy working on making index's for books (Thats his job, he makes index's for books. I thought the author did it but they have someone else do it.)
Someone needs to give those guys from OSU a good talking to about how to not look like cranks. Number 1: At the end of your article don't imply paleontologists are persecuting your idea.<<
Go for it.
"In BCF, the modern bird assembles itself part by part, each new part being an incremental improvement to an arboreal and, later, volant lifestyle."
Pardon me, but I do believe your teleology is showing.
Posted by: protest fish | June 12, 2009 1:07 PM
Hmmm...This argument and terminology is the same one used years ago by someone posting on this list...Using an alias?
I've a wacky idea. What if the 'four winged' dromaeosaurids had nothing to do with birds at all? What if they independantly evolved a primative 'flight'?
#56
I was the one who "years ago" suggested that BCF was teleological. It's also been said many times before I did.
Now, the poster named 'poster fish' says the exact same thing. No Tracy, this is not because 'poster fish' is an alias of mine (!). It's because BCF is teleological! It's as obvious as the nose on your face! No surprise, then, that several people have come to the same conclusion independently: BCF is teleological.
Dartian @44
"Huh? A rank is something relative! For example: in the Linnaean system, 'Family' is a higher category than 'Genus' but a lower category than 'Order'. (Or to take another example: in military hierachy - surely the ultimate ranked system! - 'Colonel' is higher than 'Major' but lower than 'General'.)"
Yes, I know this. But how do compare one Class with another Class? Answer: You can't.
Linnaean classification gives us Class Aves (birds) and Class Reptilia. Yet, birds evolved from within the Reptilia. Aves is a subset of Theropoda, which is a subset of Dinosauria, which is a subset of Archosauria, which is a subset of Diapsida, which is a subset of Reptilia. Yet, the Linnaean system says that Aves and Reptilia are both of equal rank (=both "Classes")!
So converting this into your military analogy, if we equate "Class" with "General", you have General higher than a Colonel, Colonel higher than a Major, Major higher than a Lieutenant... but Lieutenant higher than a General!
There are even more extreme examples in invertebrate zoology. Many groups that were once called "Phylum" under the Linnaean system have now been sunk into families!
G.Olshevsky #33
"What falsifies the BADD theory, whose major scenario is the assembly of a flying bird from components that evolved entirely in a terrestrial, nonvolant context, is the sheer unlikelihood of this sequence of events."
This is arrant nonsense. Your assertion is not "falsification". It is simply your opinion, nothing else. In science, there is no such thing as "falsification by opinion". You need hard data to refute a hypothesis, not handwaving and empty rhetoric.
Also, I would add that the "terrestrial vs. arboreal" dichotomy is old hat. The dichotomy is arbitrary and artificial, and we moved away from the old "ground-up" vs. trees-down" debate back in the 1990's. Many current hypotheses on the origin of avian flight incorporate BOTH arboreal and terrestrial ecomorphologies. After all, this is what current data suggest. As one example, refer to Glen and Bennett's recent study on claw curvature in _Archaeopteryx_ and other birds.
BCF is a lot like BAND. Both blithely ignore any and all studies published since the 1980's. Let's NOT do the time warp again.
Zach Miller @47
"George, please don't use the jigsaw analogy. It's what Creationists and ID'ers use to downplay evolution. We don't need any self-respecting scientists using the jigsaw analogy. The piece-by-piece model is perfectly obtainable in a dinosaurian ancestor."
Beautifully said. There are many sensible current hypotheses on the origin of avian flight that incorporate the principle of 'exaptation'. In the context of the origin of avian flight, this says that many avian characters evolved in a terrestrial ecology, but were later recruited (exapted) for aerial locomotion in the line leading to modern birds.
For some reason, George seems to think that any character that is important in avian flight (bipedalism, pneumatic bones, furcula, feathers, etc) must have originally evolved for aerial locomotion. This idea is very outdated, and completely unnecessary.
By contrast, the most well-supported current hypotheses have an important role for exaptation in the origin of avian flight. Many avian characters evolved in terrestrial ancestors (bipedalism, pneumatic bones, furcula, protofeathers, etc), and some may have evolved during or after a subsequent shift to arboreality (enlarged and bipinnate feathers, reversed hallux, pygostyle, etc). In short, both terrestrial and arboreal ecologies were important in the "piece-by-piece" evolution of the modern avian bauplan. This is not "unlikely", and certainly not "impossible". In fact, it's what the fossil evidence has been telling us for a long time.
This is entirely possible.
But it is not the most parsimonious possibility. In other words, it requires a greater number of extra assumptions than the idea that flight evolved only once.
The idea behind science is that you should only pull as many assumptions out of your ass as you really, really have to. :-)
T. Williams:
Well, in the sentence of yours that I originally quoted you first said that knowing the relative position of taxa is important. But then you said that ranks - which, by definition, are relative positions - are not. That did sound rather inconsistent to me.
And you didn't explain why you think the Linnaean system is impractical. Please do; I'd like to hear why you think that.
"Many" former invertebrate phyla are now considered families? Such as?
Sorry, but I don't believe birds evolved the ability to fly by first running around on the ground flapping their arms (feathered or otherwise), by hurling themselves off cliffs, by saltating across sand dunes, by running up trees with the aid of forelimbs that had turned into wings for reasons unrelated to flight, and so forth. They acquired flight simply as a series of adaptations to life in the treetops, where gravitational energy is free for the taking and the dangers of falling from great height are omnipresent. Those forms that at various times discontinued living in the trees in favor of a terrestrial lifestyle took whatever arboreal adaptations they had acquired with them and continued to evolve in other directions, giving rise to the various groups and subgroups of dinosaurs. Again, what is unreasonable about this scenario, and unparsimonious?
That "relative position" was clearly supposed to be the phylogenetic position, the relative position of species to each other in the tree. Ranks are relative in an entirely different way; it just so happens that the same word is used for both.
Come on, nobody has seriously proposed these for decades (Burger & Chiappe 1998 excepted... not sure how that got into Nature).
I think that wings came before flight and evolved for something unrelated to flight, as explained near the beginning of comment 43.
For the third time, why did the birds ever lose the ability to sprawl their legs?
Come on. Every single clade that branches off from the "central trunk" convergently evolving the same thing is the least parsimonious option.
I'll help David out by asking the question myself (making it the fourth time the question has been asked):
WHY THE HECK DID BIRDS EVER LOSE THE ABILITY TO SPRAWL THEIR LEGS?!?!?!?!
Two quick responses to G.Olshevsky's post @64.
1. When you say "I don't believe birds evolved the ability to fly by..." and go on to list several scenarios (such as WAIR), in no case do you actually *refute* any of these scenarios. The operative word here is "believe". Scientifically, this holds no water.
2. The following statement immediately puts up a red flag: "They acquired flight simply as a series of adaptations to life in the treetops, where gravitational energy is free for the taking."
While it is true that flight would be "easier" to evolve with the assistance of gravity (such as when leaping from a height, = "trees-down"), this is not an evolutionary argument. It is teleology. Evolution cannot know which path to flight is faster or easier ("trees-down" vs. "ground-up"), without already knowing the end-point. Thus, to argue that "trees-down" is preferable to "ground-up" because the former (but not the latter) can exploit gravity is teleological.
As long as a "ground-up" scenario is biophysically or biomechanically possible (and you have yet to prove otherwise), your "gravity is free for the taking" argument in favor of "trees-down" is irrelevant.
Dutian @63:
"Well, in the sentence of yours that I originally quoted you first said that knowing the relative position of taxa is important. But then you said that ranks - which, by definition, are relative positions - are not. That did sound rather inconsistent to me."
Ranks are not just *relative* positions. They purport to have *absolute* positions too. Thus, Linnean taxonomy includes many Phyla, Classes, Orders, Suborders, etc. But it's useless to equate one "Class" with another "Class", despite these being of the same "rank". Same for Phyla, Orders, Suborders, etc.
"And you didn't explain why you think the Linnaean system is impractical. Please do; I'd like to hear why you think that."
I gave an example of why Linnaean taxonomy is impractical. As birds ("Class Aves") are a subset of theropods, and theropods are a subset of dinosaurs, and dinosaurs are a subset of archosaurs, and archosaurs are a subset of diapsids, and diapsids are a subset of reptiles... how "practical" is it to have both Aves and Reptilia as "Classes" of (supposedly) equal "rank"?
""Many" former invertebrate phyla are now considered families? Such as?"
Two examples I can think of off the top of my head are two former "Phyla" of highly unusual worms, the Vestimentifera and Pogonophora. Both are now regarded as members of the Siboglinidae, which is a family of polychaete annelids.
Tracy Ford @57:
"I've a wacky idea. What if the 'four winged' dromaeosaurids had nothing to do with birds at all? What if they independantly evolved a primative 'flight'?"
Tracy, I think you're right. It's not a "wacky" idea at all.
The 4-winged dromaeosaurs and birds might well have inherited aerodynamic feathers from a common ancestor. However, as you say, the two groups may represent independent experiments in flight.
I've a wacky idea. What if the 'four winged' dromaeosaurids had nothing to do with birds at all? What if they independantly evolved a primative 'flight'?
This is entirely possible.
But it is not the most parsimonious possibility. In other words, it requires a greater number of extra assumptions than the idea that flight evolved only once.
The idea behind science is that you should only pull as many assumptions out of your ass as you really, really have to. :-)<<
There was more than 50 MILLION years (I think) from Archaeopteryx to the 4 winged dromaeosaurids. 15 mya less than the Late Cretaceous to now, why couldn't there have been more than one group of flying theropods that independalty discovered flight? I believe this that only ONE group leard to fly is idiotic. We can assume that because birds are the only existing flying theropod that only birds and thier direct ancestors flew. In all that time other animals must have evolved to fly. After all, bats evolved quickly after the K/T boundary.
56
"In BCF, the modern bird assembles itself part by part, each new part being an incremental improvement to an arboreal and, later, volant lifestyle."
Pardon me, but I do believe your teleology is showing.
Posted by: protest fish | June 12, 2009 1:07 PM
Hmmm...This argument and terminology is the same one used years ago by someone posting on this list...Using an alias?<<
Paranoia, you gotta love it. I never mentioned the person with whom I was talking about. What is they say about guilty people...This is like watching some crime movie and the perp says something only he would know and the dective never mentioned it, so only he would know.
I'll help David out by asking the question myself (making it the fourth time the question has been asked):
WHY THE HECK DID BIRDS EVER LOSE THE ABILITY TO SPRAWL THEIR LEGS?!?!?!?!<<
Theres something else people don't address (or I could be wrong) why the stiff ankle? Birds and dinosaurs don't twist thier ankles to turn. Its all done at the knee (in birds). I'd be far better to jump and land on a stiff ankle than a moveable one.
Tracy, I've got no involvement in the argument, or background in the topic, but why on earth would you think it proves anything that "someone who had used the teleology argument before" responded to your comment that perhaps "someone who had used the teleology argument before" was using an alias?! You're not coming across terribly well in the debate, I'm afraid.
This comment applies only to the main blog posting.
The existence of an unbroken lineage from the first stem-archosaur to modern birds is of course obviously true, as it is of all of its living descendants. Presumably what is meant by this accusation of âtrunknessâ is some kind of common identity, but that is no problem. The common identity of small arboreal forms is fine. They preserve particularly badly of course (see below, as has been explained for years) but it has been well established that the resistance of animals to extinction is related to their mobility, and inversely to their size. That is why we shouldnât be surprised if you see a âtrunkâ and it turns out to be of small aeronautic types.
The size and mobility factors go a long way to explaining why most warm-blooded land animals, and most complex âcoldâ-blooded land animals, can fly. Flight takes a while to perfect, especially with competitors around who have already mastered it, and in large animals it may require the evolution of warm-bloodedness, but tree-living archosaurs with even rudimentary aeronautic ability would sustain a lineage better than those without it.
Of course it didnât occur to Naish that his alternative of large land-dwelling forms is just as much a trunk, but one which violates what we know about survivability.
What a strange criticism. Itâs true of the lineage to birds, just as it is to that of crocodiles. The idea of Birds Came First was to emphasise the identity - all right, letâs call it a strangler-fig-trunk, as of course it would be multi-stranded - of small arboreal forms, typically gliders, which were more similar to what we call âbirdsâ than they are to ground stompers. That the first criticism of BCF is an accusation of teleological fallacy is presumably an attempt to suggest some kind of intellectual inadequacy on the part of BCFâs supporters, the earliest of whom were familiar with and understood the term âteleological fallacyâ 35 years ago.
Exactly. So often, he seems to want to prove his theories right by first assuming they are right.
Wrong. It is unscientific to insist that everything the other personâs theory predicts has already been discovered; and going on to rescind this requirement for oneâs own theories is hypocritical as well as being additionally unscientific through inconsistency.
Quite the contrary (see below).
...but he then describes how both theories predict them! Whether present or absent, it therefore has the same significance for both theories!
This is a demonstration of one of the foundations of folly behind an enormous amount of substandard thinking. A person knowing lakes but seeing the sea for the first time and knowing nothing about it would know he was not justified in assuming it contained no fish, just because heâd seen none come out of it yet.
Many people erroneously claim âabsence of evidence is not evidence of absenceâ even in circumstances where thatâs false, while at other times they insist âabsence of evidence *is always* evidence of absenceâ, which Naish implies here.
Scientific hypotheses are not âsupposed to be constructedâ in any way - they can and have been simply dreamed. Hypotheses only have to *explain* the evidence well.
Of course âconstructing hypotheses based on the evidence we haveâ could at a stretch be applied to the explanation-based definition above, but all too often people make the mistake of assuming - and demanding - that a theory should contain nothing but what we have already seen.
When youâve genuinely *proved* something required by a theory is most unlikely to have existed, *thatâs* when you can call an absence a refutation.
Well, the evidence we see is 100% consistent with BCF, and is nowhere near as consistent with the alternative. In terms of âabsenceâ of small arboreal forms, we donât have an absence, especially since it is 100% certain that fossilisation is much less likely for light hollow bones of gliders in acid soils. That is why the explosion of fossils only appears after independence from forests became common.
They are in his theory. Again, we see the attempt to assume oneâs own theory is certain, and then call a simple clash of theories a problem for the other side. A piece of my theory isnât at fault because it clashes with bits of your theory. The *whole* of my theory must be weighed by its explanatory power.
No it wouldnât because BCF is a quality theory that would never predict the evolution of such forms before their ancestors left the trees.
Yet again - thatâs what he thinks. Of course that says nothing about the validity of the belief that Megalancosaurus throws light on the ancestry of archosaurs. If all archosaurs - even disparate branches - had an ancestor with dorsal gliding plumes (and how disappointing but predictable that Naish didnât mention let alone offer any explanation for the drepanosaursâ extraordinary dorsal construction, jointed in the case of Megalancosaurus), then anything that could have descended from a plumed gliding protoarchosaur MRCA in the Permian is evidence for BCF and against the alternative(s). Any supposed âevidenceâ about relationships based on cladograms of these very basal archosaur-like groups is more unreliable than most since they are prone to complete rearrangement with every new study.
On the contrary - there are both similarities and differences between these plumes and modern feathers, which is exactly what you see in distantly related homologues. It is because the arguments I have to oppose here are of such poor quality that it feels ridiculous to me to treat it as a discussion rather than a commentary on a comedy of errors.
Back in the day, before the Chinese fossils, this problem was so obvious anyone could see it. In fact, the BCF (indeed the Paulian) view that types like Archaeopteryx gave rise to other mani...s predicted that manis could start to appear any time just after or pretty well at the time we first see Archaeopteryx (Ax.). Now, weâve got them in, eg, the Morrison troodont. (This looks like a snapshot of the state that dromaeosaurs had achieved. Specialised dromaeosaur teeth - note: the teeth evolve fastest - in a relatively unspecialised body.) But the problem remains - where are the *pre*-Ax manis?? Why did all this group suddenly emerge from nowhere? It is a deception to say:
This is something that BCF can explain and the alternatives canât! â...not well understoodâ actually means ânot well predicted by the non-BCF theory but letâs not mention how well BCF predicts it.â Again here, what does come through loud and clear is that the more weakly supported theory is supported by those with a weaker understanding of the nature of evidence. Although there is a geological reason why mid-Jurassic dinobirds/dinosaur fossils in general are rare, the absence of maniâs prior to Ax, if it can be separated out as an issue on its own, is just another example of pro-BCF evidence.
Eshanosaurus is vey problematic, and anyway, itâs unwise to tangle with therizinosaurs - though I doubt youâd get genuine ones from the early Jurassic even though later forms appear from egg evidence to be polyphyletic.
In my version of the tree shown at this point, troos evolve before and are swapped with ovis, which evolved from vodroms.
Without going in detail into what was said about evolution to or from small size, all the size evidence is consistent with BCF.
Yes, all the multifarious aspects of the wing: skeleton, muscles and all flight-specialised aspects of feathers evolved under aeronautic constraints. Why do I know this? Because unlike any dinobird palaeontologist living or dead, I have attempted design through simulated evolution. Even though I understood it beforehand as well as Olshevsky also did without that experience, the extent to which evolution must be led through sustained and gradual stages has been deeply engrained in my mind. You could only posit simultaneous evolution of six or more novel and temporarily unhelpful features if you had been never hoped in vain for weeks for two or three to evolve together.
Naishâs attempt to show that feathers evolved long before anything remotely bird-shaped appeared...
...assumes his phylogeny is right, again begging the question - the trade mark of the dinobird cladist, and this time he combines it with the presumption that cladogram-based phylogeny is unquestionable, a view I thought heâd recently denied. Actually though, just because arms suitable for aeronautics evolved prior to powered flight, it doesnât show they werenât evolved through aeronautical pressures.
There is plenty of evidence that more basal forms had wing-like arms, though not everyone endorses the phylogeny implied by âbasal coelurosaursâ. Protoavis had wing-like arms, and so did Scansoriopteryx.
Wing assisted inclined running is a form of powered flight, and the idea that it was involved in the evolution of flight requires that clawed hands be abandoned for climbing until they were optimised for flight, which obviously couldnât be realistically imagined in any scenario.
And the âWrapping it all upâ paragraph embodies all the fallacies. Iâll refrain from commenting on: âFor previous articles on non-standard phylogenetic hypotheses see...â.
Presumably they don't need to. Adding that ability might have a cost, in terms of extra mobility in the joint, which needs extra ligaments etc to support it. Apes need to sprawl since they rely on legs to move, but birds don't need to sprawl to move now they don't have a long bony tail to support in flight.
Actually, there is a photo of a modern bird standing on reeds in a sprawling position.
John Jackson: I hope you have forgiven me for my nasty comments a while back. Again, no one here should be adressed like that, I apoligize.
"Actually, there is a photo of a modern bird standing on reeds in a sprawling posistion."
You see, this bird (I forgot its name) has secondarily regained the ability to sprawl its legs. Basal birds had a fully erect stance. Why did birds lose the ability to sprawl their legs in the first place? It's such a good posture for climbing that said modern bird has gained it back! (BTW, thanks for the response, but the question was intended for George Olshevsky, who doesn't seem to want to answer it, despite its being asked three times already by David Marjanovic.)
I am very sorry for those rude comments of mine (the "idiot" ones). However, that still doesn't change the fact that this John Jackson dude needs to leave the Tet Zoo and never come back. There's got to be some other blog out there somewhere that will adopt him and give him a warm, loving home in which to live.
Perhaps the same one that took in Peter Mahilda. (Does ol' Pete have a blog home right now? He doesn't appear to be bombarding us Tet Zooers anymore.)
That's Mihalda, not "Mahilda".
I have only one thing to say in response to John Jackson. BCF is completely unsatisfactory and at odds with the evidence.
Beautifuly said, Darren. Let's all just leave it at that.
@ #21, aka Brian Beatty
Yes, and it's tragic that I can't even spell my last name right... ;)
A few brief comments to J.Jackson's long post:
(1) Any claim that "trees-down" is preferable to "ground-up" because the former is "easier" is certainly teleological. It is teleological because it implies that evolution has a choice. In fact, evolution can only act on what is available. If a terrestrial theropod is engaged in incipient aerial activities (e.g. for climbing dunes, catching flying insects, whatever), and further refinements of aerial behavior are favored, evolution is not going to say "Hang on, this aerial behavior would be so much better if you were arboreal".
I don't disagree that "ground-up" is more biophysically challenging than "trees-down" (because gravity can be used to build airspeed, instead of acting in opposition). However, in the final analysis, this means absolutely nothing. If it is biophysically feasible for a terrestrial animal to evolve flight, then "ground-up" scenarios cannot be removed from consideration. Just because somebody deems them "unlikely" (in his/her opinion) is not a reason.
(2) Longisquama's dorsal structures have nothing to do with feathers. There is no evidence that there are homologous, and plenty of evidence that they are *not* homologous.
(3) BCF is not a "hypothesis" - and it is certainly not a "theory"! It is a historical-narrative scenario. Others have called it a "just-so" story. What is required is for BCF to be broken down into explicit hypotheses. This way, BCF can be tested - which is the first step in the construction of a hypothesis.
As it stands, BCF is directly contradicted by phylogenetic analysis. This is because (as Darren stated) the character distribution required by BCF (especially having arboreal/aerial characters at every major branching point) is at odds with the character distribution posited by phylogenetic analysis. Yes, this is 'cladistics'. Sorry, but there are good reasons (scientifically speaking) why people use this method, even if you don't like it.
T.Ford @56
Sorry Tracy, I'm at a loss. I have no idea what you're on about. But it's nice to know I'm not the only one.
Actually, there is a photo of a modern bird standing on reeds in a sprawling position.<<
Are you sure its 'sprawling'? Our old Parakeets could 'sprawl'. They'd have one foot on the bar and the other on a swing. But I think the sprawling is at the knee jonit and not actually sprawling. I wish I could have made an x-ray to make sure.
David:
T. Williams' original response was not to me but to Michael Erickson who, by his own admission, was not entirely clear on the rationale behind the use of phylogenetic nomenclature. And this whole current Linnaean-vs-phylogenetic-nomenclature debate really is quite confusing, to put it mildly. Whoever is trying to present its basics should avoid ambiguous language and explain things very carefully.
T. Williams:
I'd say that in most cases, it's very practical* indeed. At least for those who only work with extant taxa (that would be the the vast majority of biologists) and not with Mesozoic dinosaurs. That dinosaur phylogeny you listed is really of little or no practical consequence to, for example, an ecologist or a biogeographer.
* Whether it's 'right' is another matter entirely.
To put it another way: There are plenty of things you can say are wrong with the Linnaean nomenclature. But it being 'impractical' is not one of them. The very fact that this system has, at least until recently, been in universal use across all of biology for over 250 years should amply illustrate that a ranked classification system must have at least some practical value. If that was not the case, it would have been replaced with something else long before Gauthier & De Queiroz came along.
I suppose that one could argue that Linnean ranks are 'useful' IF your only concern is book-keeping or classification. Fact is - and as has been argued here a few times before (examples: here and here) - they are downright misleading and should be avoided at all costs, predominantly because they are based around the idea of equivalency and are actually regarded as 'real' (=quantifiable) by some workers. You know: people regard 'Order' Squamata as somehow similar in diversity and content to 'Order' Gaviiformes. Or, they count the number of 'Families' or 'Orders' and think that they have gotten some handle on actual biodiversity.
I cannot see that there are any advantages to maintaining Linnean ranks, and fortunately the vast majority of biologists agree with me.
While I do agree with you, Darren, I don't think I'd be so quick to say that the "vast majority" of biologists do. On the other hand, I'd probably say that too many biologists haven't really given the matter a great deal of thought - "if it was good enough for Cuvier..."
Hi Chris. You're right: perhaps what I should have said was 'the vast majority of systematists'. In fact, are there any publishing systematists who champion the continued use of ranks? I mean, except Mike Benton?
I would say that Allain Dubois is probably the most prolific champion of ranks that I'm aware of at the moment. I reviewed one of his papers back in December, if you feel like a good skull-caving. I'm sure that there are more, but I can't think of them off the top of my head. I think most working systematists who are of the "you can take my paraphyla when you prise them from my cold, dead fingers" field of view* are usually big fans of ranks.
*Sadly, considering the average age of most working systematists, the day of said prising is in many cases probably not too far away.
Oops, just in case I made any inadvertent implications, I didn't mean to say that Dubois is a fan of paraphyla. I don't know what his attitudes are in that respect.
First of all, Tracy: please put "<blockquote>" in front of everything you cite, and "</blockquote>" behind it (without the quotation marks obviously).
Actually about 30 million years -- Archie: 150 Ma ago, Microraptor: about 120 or a bit less).
Of course this could be the case. We just have no evidence that this actually was the case, and we have no other reason to suspect it happened either (evolving flight isn't that easy, or it wouldn't have happened only 4 times in total).
Yes, but only once, and into a niche that the birds had left empty...
As far as I know, he doesn't like them, but I don't know how far he goes with that. He's slowly... very slowly, though... warming up to the PhyloCode as his misunderstandings about it disappear one by one and as his proposals to amend the ICZN (by including the higher ranks, by requiring a definition that contains one diagnostic character, and many more) get rejected one by one.
I have to go, more later.
That's too bad, as amendments like that would go a long way to fixing the most commonly cited problem with ranks (lack of standardization).
Darren:
Be careful with what you call 'facts' here! Nomenclature is not, and can not be, science. Biological nomenclature - like any other nomenclature - is a set of conventions, and the point and purpose of having one is to facilitate communication between biologists from different fields. Thus, this is not a scientific dispute and the question of who has the 'facts' on his side is moot.
(Actually, Iâd go so far as to say that this nomenclatural kerfuffle is ultimately a question of personal preference. And peopleâs preferences differ. Mine happen to be different from yours, or David MarjanoviÄâs, regarding this particular issue.)
Of course, a nomenclatural system ought to be as universally used as possible. It is not desirable to have a situation where some biological sub-disciplines/individual biologists use a rank-free system, and others use a ranked system. For my part, I support majority rule in this instance. If there is a sea change in opinion in favour of the use of phylogenetic nomenclature, across all of biology; well, then I, too, will follow suit and I wonât oppose it for the sake of opposing. The greater good and all that. But as long as adherents of the Linnaean nomenclatural system still are in the overall majority - as Iâm fairly certain that they are - I am in no hurry to leave that camp.
This holds for running as well as for jumping and landing.
You know, in 1990 or so Nicholas Hotton III suggested that mammals are superior to dinosaurs (â¦it was one of the last such claims in the entire scientific literatureâ¦) because cursorial mammals retain more mobility at the hip than dinosaurs, so they can avoid damage to the ankle by positioning the leg differently when they hit uneven ground. What he overlooked is that dinosaur ankles cannot be damaged without breaking bone: they're solid hinges, unlike the complicated ankles of even cursorial mammals that are composed of many bones that can slide past each other.
Come on! We're talking about r-selected animals here! Your sample contains too many big mammals, which are all K-selected.
Don't cut yourself with Ockham's Razor.
What? Where? How?
Yes. In the meantime, you simply apply the principle of parsimony.
Really, I don't get it. You harp on and on on one part of the scientific method -- falsification --, yet you completely ignore the other part -- parsimony! Why?
Excuse me. BCF says Ornithischia started in the trees. Why don't Pisanosaurus, Eocursor and/or the heterodontosaurids possess any trace of (however vestigial) adaptations to climbing???
You seem not to have read any of the papers that came out on it in the last 10 years.
Where did you get the claim from that the teeth evolve fastest? Mammals? Cichlids? LOL. Only someone utterly unfamiliar with dinosaurs could make such a claim.
There are dromaeosaurine teeth all the way down to Guimarota (Kimmeridgian), and "velociraptorine" ( = plesiomorphic dromaeosaurid-sensu-lato) teeth go down to at least the same time (Morrison, Guimarota), possibly even the Middle Jurassic (in Scotland and Russia).
And how do troodontids have a "relatively unspecialised body"? What about the metatarsus and the short arms?
Aaah, cladistics with three characters! How⦠refreshing.
Well, duh. Everything and its opposite is consistent with BCF in this respect, because Cope's Rule is bullshit.
<headdesk>
One word: exaptation. Look it up.
PAR-SI-MO-NYYY!!!
Protoavis is a chimera consisting of drepanosaurid and theropod material among many others. The forelimb material is badly crushed; from Chatterjee's own photos (1999) you can see that the "quill knobs" are bogus.
You have it backward. Being able to sprawl is normal. Why did the ancestors of the birds ever lose it? Remember that BCF says the ancestors of the birds all the way down to the lizard-shaped animals at the base of Archosauromorpha were arboreal. Why would a lizard-shaped climbing animal, or any still climbing descendant of such an animal, ever lose the ability to sprawl?
BAD explains this easily: it's an adaptation to running that occurred in the earliest dinosauromorphs. When birds became arboreal (several times independently), they were stuck with this architecture.
I'm talking about climbing, arboreal birds.
Yes, there are a few passerines that have regained the ability. Why are they the glaring exception rather than the rule? Why can't all birds (except maybe for the most highly cursorial ones) sprawl?
========================================
Body stratotypes also had some practical value, but they've still been replaced by boundary stratotypes because these have even more practical value.
As for outright problems with rank-based nomenclature, I mentioned a big one about 2/3 down the length of comment 43.
The ones I mentioned wouldn't solve a single problem about ranks. They'd solve two other problems about the ICZN:
1) The ranks above the family group are currently not regulated except for spelling; priority does not apply, and there are no types. This is how Microsauria lost Hylonomus and Cotylosauria lost Empedocles (junior synonym of Diadectes).
2) Regulated taxon names are defined by type and rank, but the ranks aren't defined, so you can split and lump as you like (only the type has to stay inside). Making a diagnostic character part of the definition would restrict that.
Now that I am all cleared up (through everyone's responses to me, and through much more personal research) on how cladistics works and how useful it is, I will say that Darren is 100% RIGHT. We should not maintain Linnaean ranks. They are worthless and downrght misleading. Figuratively speaking, they should die.
David Marjanovic wrote:
Hotton said that? Are you sure? He was the first to propose the concept of the "endothermocentric fallacy" (i.e. warm-blooded = better), and has shown, on at least two separate occasions, why mammals should not be viewed as the pinnacles of evolution. I find it hard to believe that after doing all that, he would go off and say that mammals were "better" than dinosaurs.
By chance are you referring to his 94 Dino Fest paper (Why Dinosaurs Were Not Mammals)? He gave a mention of the different ankle designs between both groups, but there was no mention of superiority.
Possibly -- in which case I'm confusing him with the guy who actually made the proposal.
It's been a long time, and I only read it once. It was in a book, that much I'm sure about...
could be Alan Charig.
======================
The Center for North American Herpetology (that is, Joseph T. Collins) has decided to restrict the term "reptiles" to Squamata or Lepidosauria (hard to tell) and now talks all the time about "amphibians, turtles, reptiles, and crocodylians of North America" or "reptiles and turtles of Kansas".
How useful is it really to lump turtles, lepidosaurs and crocodylians together? Let alone to treat this grouping as somehow an equal to the birds?
Ecology perhaps, but you can't do biogeography without a good phylogeny; and if you want to talk about phylogeny, rank-based nomenclature is not the easiest choice.
Michael:
If you think phylogenetic nomenclature should be used instead of the traditional Linnaean one, fine. That's not an unreasonable opinion (although it's not one that I myself hold). But form your opinions, whatever they may be, for the right reasons. Rejecting the Linnaean system because you think cladistics is incompatible with it is not a good reason. It's not a good reason because it isn't correct. Cladistics* is only a method to reconstruct relationships, and it is compatible with both ranked and rank-free nomenclatural systems.
* It may be noted here that the journal Cladistics has published many papers over the last few years that explicitly oppose the use of phylogenetic nomenclature. So no, the use of cladistic methods and rank-free nomenclature don't automatically go hand in hand.
Also, another not-so-good reason to hold a particular opinion is because some Really Cool Guy holds it too. Science is not hero worship. Find things out and think for yourself, and then form your opinion. And remember that reasonable people can reasonably disagree about things.
One more piece of advice: hyperbole - even if it's only in jest - usually does more harm than good. Especially in internet discussions where nuance easily gets lost and people are particularly prone to misunderstand each other. Use it only with great caution.
(Every single one of them based on crass misunderstandings by people who evidently never read the whole PhyloCode, even though it's much shorter and much more readable than the ICZN or the ICBN. But I digress.)
Linnean taxonomy has an important function: it keeps people out of trouble who would otherwise be bothering phylogeneticists. If taxonomists could be persuaded to stop re-assigning species to random new genera in a futile attempt to try to make genera monophyletic, everybody could be happy. The taxonomists could go wild naming families, subfamilies, suborders, superfamilies, and what-have-you, and shuffling species in and out of them, and the rest of us could ignore them entirely. It's when their antics leak into the binomena that they cause confusion.
Millions of people spent their early adulthood committing to memory the thousands of binomena they need for their work. Changes to those names only cause communication problems, without providing any benefit. Many people are starting to rebel, and continue using the "old" binomena , which still work as well as ever.
Dartian: Nearly everything you said and/or assumed about me and about how and why I form my opinions is wrong. I could sit here and defend myself until Kingdom come, but I think I'll wait for when I really need to. All I'll say is that just because you change your mind after talking things over with others and rethinking the evidence at hand doesn't mean you're not thinking for yourself. I am a VERY independently thinking person.
"Ergo, there is no 'wing problem'."
You do not understand the functional, mechanical morphology of the evolution of bird flight. WAIR uses modern birds with growing wings and the instinct to use them. This has nothing to do with the origin of bird flight.
"Finally, the 'wing problem' argues that the standard model provides no obvious explanation for the evolution of the avian wing, and that the wing most likely evolved in an arboreal setting among dingo-birds."
Birds are not arboreal, they may nest on them, but they do not live in them. Arboreal animals like sloths, koalas, monkeys, squirrels and lizards feed in the trees where they live, birds do not! If birds fed in the trees they lived in, what do they need wings for!?
Knowing the how and why flight evolved will explain which species did it. BSF, BAND, BAD, are irrelevant concepts for the evolution of bird flight!
Birds did not evolve flight from any impossible tree-down or ground-up scenarios, they did it by "bank-jumping plunge-diving" (BJPD.) This explains how they became airborne, what they succeeded in doing and how they survived failure. Ergo, natural selection for adaptations that work!
protoart@gmail.com
I have no particular interest in the question of the origins of bird flight, so I won't comment on that, but I will on this:
Say what?! No birds are arboreal and no birds feed in trees? In what meaningful sense of the word 'live' do woodpeckers not live in the trees? Most of them certainly feed there.
And in addition to woodpeckers there are plenty of other bird species too that spend most of their time in trees, and also feed there. Some even climb tree trunks and branches. (If you don't believe me, I suggest you grab yourself a pair of binoculars and go to the nearest park or patch of forest, and observe for yourself.) You need to define what, exactly, you mean with 'arboreal'.
From Wiktionary: arboreal 1. of, relating to, or resembling a tree.
Most birds do not relate to trees. The red-footed booby has webbed feet and nests 'on', not 'in', a tree and certainly doesn't feed there.
I took my binoculars outside, just now, and saw sparrows nesting under roof tiles. Ergo, they are apartment dwellers.
The mindset that birds are arboreal afflicts those that propose birds flight evolved "tree-down." Suicide is a bad mutation.
Arthur:
Cute. But please answer my woodpecker question. If they don't live in trees, then where do they live, according to you?
Some woodpeckers live in tree holes but they don't feed in that tree. Some woodpeckers live in dead trees, poles or cacti.
To say arboreal means to have adaptations that are required to survive there. A fish is an aquatic animal. A bison is terrestrial, etc. Some owls live in tree holes and some burrow in the ground. Are they terrestrial?
Flying squirrels and draco lizards are arboreal. They have climbing, jumping, gripping, fully adapted forelimbs like their non gliding arboreal cousins. They also have wings but can't evolve flapping and survive in the transition. Which is why I say arboreal animals didn't evolve flight.
Arthur:
That's an understatement; almost* all of the world's about 200 species of woodpecker nest in tree holes (or cactus holes).
* The only exceptions, AFAIK, are a couple of terrestrial(!) woodpecker species that live in treeless areas in Africa and South America, respectively. They nest in holes they escavate in river banks or among rocks.
No, but those woodpeckers then usually feed in another tree.
I don't really see what difference it makes if the tree the woodpecker climbs is living or dead, or if what it's climbing is actually a saguaro cactus. The point is that the woodpecker gets up the trunk by climbing - not flying.
Woodpeckers have plenty of such adaptations. Check out, for example, this old Tet Zoo post, and look up the references therein. (By the way, Darren: there are - again! - active spambot links at the end of that post's comment section.)
First, a nitpick: the burrowing owl Speotyto cunicularia doesn't burrow holes itself, it moves into abandoned rodent burrows. As for your specific question: I certainly would call this owl terrestrial. Seriously, what else would one call it?
Actually, I get the impression that your personal criteria for what's 'arboreal' and what's 'terrestrial' are excessively strict and quite non-mainstream. Do you consider the booby you mentioned earlier 'marine/aquatic' or not?
Well, you might actually end up being correct with that last part. I'd like to repeat that the evolution of bird flight is not a topic that I have any specific - as opposed to casual - interest in. And your BJPD hypothesis, as far as I understand it, at least seems to be original, I got to admit. (I'll leave it to others to discuss its scientific merits.) But I don't think you should support your hypothesis by using arguments that require resorting to semantics (e.g., having to quibble over what 'arboreal' means), or that are demonstrably untrue (e.g., claiming that birds don't feed in trees, while in truth, many do).
I've run this past you several times. Birds don't feed in the tree where they nest. They want isolation and no competitors or predators around. They do feed in other trees which they reach by flying not by climbing. Ergo, they are not arboreal.
Arthur:
What has that do with being arboreal? Are you suggesting that a woodpecker (or a nuthatch, or a treecreeper, or a sittella, or some other trunk-climbing and trunk-foraging bird) doesn't qualify as 'arboreal' because it doesn't spend its entire life - from birth to death and everything in between - in the same tree?
By that logic, very few, or possibly no vertebrate species would meet the criteria of 'arboreal'. None of the animals you mentioned in post #104 would qualify. Squirrels are in no way restricted* to feeding in the same tree where their nest is; they feed freely in other trees (and depending on the species, sometimes even on the ground). Draco lizards don't feed in the same tree where they nest because they don't nest in trees in the first place; they lay their eggs on the ground. Sloths, koalas and monkeys don't have nests at all; they carry their young around, and they are in no way restricted to any one particular tree either. Why are you using stricter criteria for birds than for non-birds?
* This should be self-evident, but I'll say it anyway: any tree-living vertebrate must sooner or later (and usually sooner rather than later) move to a new tree. There are plenty of both short-term and long-term reasons for that: resource depletion, inbreeding avoidance, predator threat, etc. This is equally true for a woodpecker as it is for a koala or a squirrel.
But that is true of pretty much any organism, regardless of what environment it lives in, so I don't really think it is a particularly useful argument here.
Again, what does that really have to do with otherwise being arboreal? Flying is just those birds' method of reaching another tree. Other arboreal animals travel between trees by, e.g., gliding, parachuting, leaping, or descending to the ground. Can you give a non-subjective explanation as to why flying would be so fundamentally different - in this particular ecological context we're discussing - as a way of moving from tree to tree?
Finally, if you think I'm being unreasonable with my objections, I'm not. Remember that it's you who are proposing a novel idea; it's you who need to present your case in a clear and consistent way so that others don't misunderstand you. And to be honest, the way you've presented your definition of 'arboreal' thus far, you are rather giving the impression that you apply different standards to birds and to non-birds.
Why is it that the dinosaur posts always atract the loony bins?