Nova-"The Four-Winged Dinosaur"

[Bikewer]

Nice Nova episode airing tonight on speculations about the evolution of flight, concerning the "four-winged" microraptor found fairly recently in China.

Nice interplay (and argument) between the competing schools of thought.

[MrQhuest]

http://www.pbs.org/wgbh/nova/microraptor/fossils.html

Missed the article, but from what I can tell, the animal did not have 2 sets of wings, but a feathered set of hind limbs.
When I saw 'four-winged dinosaur,' I read that as two sets of wings and one set of legs. A six limbed dinosaur/bird would have been a major deviation from the evolutionary record. Specialized hind legs however, is possible, even expected.
Nifty fossils though.

MrQhuest

[Tumblehome]

Yes, "four wings" isn't accurate. I saw the show last night, and it concluded that these creatures didn't actually fly, but were gliders since they lacked the shoulder configuration to flap their wings. Feathers on their legs helped them to glide farther, and by lowering their legs, the feathers acted as a brake to slow their speed before landing. Today's birds do that by flapping their wings differently so there's no need for feathers on their legs.

If the creature was just a glider, though, it makes you wonder how it got up into a tree in the first place.

[Charlie Monoxide]

Wow, great fossils. I hope to catch this Nova re-run.

Lord knows we found another "gap" for the creationists/ID'ers to exploit ...

Charlie (gaps, like David Letterman's teeth) Monoxide

[BenBurch]

I think a feathery Sugar Glider is the right visualization.

[bluecollarscientist]

Nice interplay (and argument) between the competing schools of thought.

I'm glad they depicted the controversy, but I was disappointed that the Kansas group's hypothesis and methodology was so weak. Martin et al looked a little buffoonish to me. I almost got the impression that their views were aired primarily to have a controversy to make the show a bit more dramatic, or something. I found a few of Martin's claims puzzling, and had some good answers from some paleo specialists commenting on my blog.

Despite this disappointment - which amounts to "forget these Kansas people, stick with China and AMNH" - I thought the documentary was really good. Nova rarely disappoints.

If the creature was just a glider, though, it makes you wonder how it got up into a tree in the first place.

Uh - really? How do non-flying animals get up into trees these days?

[Hokulele]

Uh - really? How do non-flying animals get up into trees these days?


Sit on an acorn and wait?

[Tumblehome]

Uh - really? How do non-flying animals get up into trees these days?


Non-flying animals have four feet with claws to help them climb trees. It seems to me that it would be more difficult for a two-legged bird to climb a tree, keeping in mind that this is much bigger than a nut hatch, and has long feathers on its legs that might hinder its climbing ability.

The Nova doc showed a bird going up a steep incline by half-running, half-flapping its wings, but the microraptor supposedly couldn't flap its wings. Is it plausible that it just jumped onto a tree trunk and walked up on its two legs?

[shadron]

Well, for one thing, this is a fossil, so I presume that in the long run its locomotion wasn't ideal for its environment, else we'd have them dive bombing us today. This is a transitional animal, not a solid niche dweller, yet.

Secondly, squirrels (even flying squirrels) have no problem even with the tail and the skin flaps hanging between the legs. All an animal of that size needs to climb vertically is claws (which this indisputably had) and a beak to assist (with teeth, no less), and trees (or reasonable facsimiles) with loose "bark". Bats climb things, albeit somewhat clumsily.

I imagine it would be a bear climbing backwards with the feathers, but squirrels don't do that either.

[ImaginalDisc]

Well, for one thing, this is a fossil, so I presume that in the long run its locomotion wasn't ideal for its environment, else we'd have them dive bombing us today. This is a transitional animal, not a solid niche dweller, yet.

This is not consistent with Evolution. The organism must have had (even a small) competitive advantage in its habitat. Perhaps it was a specialist in eating something that other organisms either could not consume or could not access. Perhaps it lived in some isolated area with few competitors. Perhaps it climbed poorly, but managed to glide between trees in the canopy relatively well, making it more adept at evading predators than its competitors. The fact is that if an organism is less than competitive in all ways in its habitat, it dies off in the twinkling of an eye, geologically speaking.

Evolution doesn't seek goals, and has no patience for weakness in a "transitional form" while it waits for the organism to evolve into something splendid.

[skeptigirl]

Here's my latest pondering the Universe question and answer seeling, for what it's worth.

It's become clear birds evolved from dinos. So, were there multiple ancestral lines or was there a single 'adam and eve' flock of dinos that went on to be the bird branch of the tree of life?

So, I looked into it and found "only the neornithine birds persevered to continue the massive diversification that began in the Cretaceous period". (http://www.ucmp.berkeley.edu/diapsids/archofr.html)

So, the next question I had was similar. How many lines of neornithine birds were there?

Current thought was that there were 3 lines of dinos with bird features.

From the Tree of Life web project (http://www.tolweb.org/Dinosauria/14883)

Ornithischia - Bird-hipped plant-eating dinosaurs
Sauropodomorpha - Long-necked plant-eating dinosaurs

Both those lines died out.

The Theropoda - (Bipedal predatory dinosaurs) evolved into birds.

From Theropoda came Coelurosauria (tyrannosaurs, Oviraptor, Velociraptor, birds, and relatives) and the other branches became extinct.

next came the following branches * Ornitholestes
* Compsognathidae
* Alvarezsauridae
* Ornithomimidae (ostrich-like dinosaurs)
* Therizinosauridae
* Tyrannosauroidea
* Maniraptora
o Oviraptorosauria
o Dromaeosauridae (Velociraptor and relatives)
o Troodontidae
o Aves (birds)

Aves then became

* Archaeopteryx
* Confuciusornithidae
* Enantiornithes
* Euornithes (true birds)
o Patagopteryx
o Hesperornithiformes
o Ichthyornithiformes
o Neornithes (modern birds)

And the neornithes branched into 3 lines of birds we have today.

Then I found my way to EvoWiki and The Neornithine 'Big Bang' (http://wiki.cotch.net/index.php/The_Neornithine_'Big_Bang') page.In light of the evaluation offered within this essay, the author submits a revised scenario to that previously advanced in Avian Phylogeny and Origins.

Originating sometime in the latest Cretaceous, within the Campanian/Maastrichtian interval, the basal neornithines, perhaps derived from forms similar to Apatornis celer and represented by the graculavids and other “transitional shorebirds,” experienced a very modest adaptive radiation within a severely restricted niche, namely, the near-shore environment. The decline of the Hesperornithiformes and Ichthyornithiformes during the later Cretaceous may have facilitated this modest diversification of the “transitional shorebird” lineage, or alternatively, may have been caused by it.

With the events at the KT Boundary (whatever those were), the dominant aviary of the Mesozoic, represented by the spectacularly diverse Enantiornithes and the scattered lineages of archaic ornithurines, were extinguished, leaving the incipient neornithine dynasty to undergo an explosive primary adaptive radiation. Within a period of some ten million years, the base of the neornithine lineage diversified so extensively that almost all extant orders were present by the Lower Eocene, as witnessed by the avifauna of such deposits as the London Clays and Green River Formation of Wyoming. With such a rapid branching of clades from their respective nodes, the ordinal relationships of Neornithes are largely unknowable, and thus we have a m�lange of taxa of uncertain affinity.

The base of Neornithes is something of a hub and spokes, with unresolved branching patterns for multiple orders in what is a thoroughly unpleasant poltyomy.

So I guess we don't yet know how many variations of these Neornithes survived the KT Boundary event. But I think this sounds like there was probably one line of descent that had already began branching into new species at the time of the KT event which survived the devastation. Sort of like having most domestic dogs surviving something that wiped out all the wild canine species and subsequently evolving.

And at least now I have a better idea where Archaeopteryx fits into the dino picture.

And it made it easier to understand what they were talking about on the NOVA program which is summarized on this page (http://www.pbs.org/wgbh/nova/microraptor/producer.html) explaining the controversies about which bird features evolved when.

Journey through time, from birds to dinosaurs (http://www.nhm.org/journey/prehist/birds/home.html)The evolution of the characters that make flight possible - feathers, lightweight bones and joints that could articulate a flapping motion and provide control during flight, probably all came about for different reasons. Once the ability to fly had evolved however, refinements in the efficiency of flight could be further evolved.


BTW, the Microraptor either has a different scientific name or it isn't listed in the Tree of Life Project yet.

[skeptigirl]

EvoWiki: Microraptor (http://wiki.cotch.net/index.php/Microraptor) has the scientific names but those are not on the TOL web project either.

But if you want to get more scientific than my Universe ponderings, EvoWiki has this interesting tidbit.
Dromaeosauridae (http://wiki.cotch.net/index.php/Dromaeosauridae)Dromaeosauridae (sensu Ostrom 1990) is an extinct family of intelligent dinosaurs known as the raptors. The Dromaeosauridae span the cretaceous period.

Common ancestor of Deinonychus + Velociraptor, and all descendant taxa.

Autapomorphies of Dromaeosauridae as outlined by Ostrom in 1990 are no longer reliable in light of new fossil evidence. In particular, the semilunate carpal and sternocostal articulations are probably symplesiomorphic of Paraves.

JGK

[Gravy]

NVM

[CFLarsen]

Um, you've never seen a woodpecker or a nuthatch or any number of other birds climb up, down, and sideways on vertical trees?

Birds don't work in horizontal/vertical frameworks. They work in all three dimensions, far more advanced than humans can fathom.

When you can just go...up, up and away, whenever you want to, your perspective tends to change dramatically.

[skeptigirl]

NVM
???Acronym Definition
NVM National Volcanic Monument
NVM Network Virtual Machine
NVM Network Virtual Memory
NVM Never Mind
NVM Non-Volatile Memory
NVM Nonvolatile Matter

I'm going to guess, nevermind. :)

[Big Les]

I've been going through all my old dinosaur notes and books from my childhood and early teens (1985-92 or thereabouts). I've been catching up over the last month or so on the last ten years I all but missed, so have recently covered much the same ground as you skeptigirl. I picked up a neat little (coffee table) book by Angela Milner called "Dinobirds" that spells it out with nice piccies for slow people like me. :)

It's so cool to see what's been learned in the meantime. Especially all the mentions of a dinosaur-bird link as just a hypothesis, when now, only a fringe of disbelievers (borderline denialists) challenge it.

[shadron]

This is not consistent with Evolution. The organism must have had (even a small) competitive advantage in its habitat. Perhaps it was a specialist in eating something that other organisms either could not consume or could not access. Perhaps it lived in some isolated area with few competitors. Perhaps it climbed poorly, but managed to glide between trees in the canopy relatively well, making it more adept at evading predators than its competitors. The fact is that if an organism is less than competitive in all ways in its habitat, it dies off in the twinkling of an eye, geologically speaking.

Evolution doesn't seek goals, and has no patience for weakness in a "transitional form" while it waits for the organism to evolve into something splendid.

You're absolutely right, but while evolution may not seek to meet a goal, it does indeed find them anyway. When the environment is in stress and changing, evolution follows willy-nilly, always imperfect, trying this and that, always somewhere behind the curve. When the environment becomes stable, evolution causes its charges to radiate into all the niches, weed out genetic weaknesses with greater strictness and become a stable population. This fact is very much apparent to those who do statistical analysis on fossil finds, as some species are very well represented because of large populations and radiation into niches, while those more transitional are scarcer as well.

[GodMark2]

I imagine it would be a bear climbing backwards with the feathers

I first read this and tried to imagine one of our furry ursine friends in a bird suit ascending a tree in reversed posture. I haven't laughed that hard in a while. Thank you. </derail>

[sinclairmcevoy]

Birds don't work in horizontal/vertical frameworks. They work in all three dimensions, far more advanced than humans can fathom.

When you can just go...up, up and away, whenever you want to, your perspective tends to change dramatically.

How many ways can a tree be climbed? Up, down and sideways on a vertical tree seems to sum it up. Am I missing something?

[CFLarsen]

How many ways can a tree be climbed? Up, down and sideways on a vertical tree seems to sum it up. Am I missing something?

That's the bottom of the trunk. Ever been high up in a tree? That will give you a very good idea of what three-dimensional is!

[neutrino_cannon]

Here's my latest pondering the Universe question and answer seeling, for what it's worth.

It's become clear birds evolved from dinos. So, were there multiple ancestral lines or was there a single 'adam and eve' flock of dinos that went on to be the bird branch of the tree of life?


This is a relative sort of question. Feathers only evolved once; or at least, that's the most reasonable guess as it would be fantastically unlikely for something as complex as a feather to evolve in exactly the same way twice under independent circumstances. Whichever lineage first evolved feathers could be considered the "Adam and Eve" flock.

(incidentally, pterosaurs were covered in in insulation that may or may not be homologous with feathers. If it is, feathers, or at least hollow proto-feather filaments may go back a lot further than direct fossil evidence indicates at this time)

But evolution doesn't go in straight lines; it prefers a tangled bush, so in that sense, yes, early bird evolution was terribly, terribly complicated.

So, I looked into it and found "only the neornithine birds persevered to continue the massive diversification that began in the Cretaceous period". (http://www.ucmp.berkeley.edu/diapsids/archofr.html)

So, the next question I had was similar. How many lines of neornithine birds were there?

"lines of neornithine birds" is something of an artificial, human distinction. If you're asking about higher level avian phylogeny... don't ask that question. Seriously, that way madness lies!

In the past decade or so, there have been a lot of big shakeups in the understanding of bird evolution; not just in terms of dinosaurs->birds, but in how the living varieties of birds are related to each other. Consequentially, one of the big "all the world's birds" books you can find at a library from several years ago will extensively and painstakingly list classification schemes for birds that are considered just plain wrong.

The advance of science, or a sinister plot to sell more bird books?

Current thought was that there were 3 lines of dinos with bird features.

...(cut)...

OK, OK, OK. You may not like this; but it's somewhat more complicated than that. Actually, it's horrifically more complicated than that, and all the details are not yet agreed upon. Life, in all its diversity, really has no obligation to make it simple though, so who are we to complain?

Again, all birds have a single common ancestor. All natural clades do. That single avian ancestor has not been discovered yet, and given the probability that any single organism gets fossilized, probably never will be. The closest approximation to an "urvogel" which is currently described is archaeopteryx. No other fossil has yet unseated archie from the coveted position of most primitive known bird, but the recent ones have done a heck of a lot to fill in the gaps.

In any discussion of bird evolution, it behooves us to say exactly what we mean by "bird". In a modern context, that's pretty obvious; living birds are very, very different from other lineages and there are no messy intermediates to complicate things. Birds have feathers; no other group does. Birds have wings, toothless bills, short, stumpy tail bones, hollow bones, and lay eggs. Some other groups have some of those same traits (turtles have toothless beaks and lay eggs), but they're fairly obviously a shared ancestral trait (eggs), or a similar looking trait that evolved independently in each group (toothless beaks). Thus, once you have figured out that bats are freakishly aberrant mammals, and that penguins and whatnot aren't that different from hummingbirds (flight is not a criterion of birdness), defining what a bird is in not hard work; the Potter Stewart Critereon works beautifully. I know a bird when I see one.

Which is what makes the discovery of fossil birds with teeth (http://www.oceansofkansas.com/Hesperornis/martin60.jpg) and feathered dinosaurs (http://dino.lm.com/images/display.php?id=2004)such a head-throbbing embuggerance to it all. All those neat categories fall to pieces, and Nature herself laughs maniacally at our attempts to confine her work to pigeonholes. Nature is vindictive that way.

So, what do we know about how Life works? We know that all life shares a common ancestor, and that the various lineages branch outwards from it fractal-like, and continue diverging. We know that populations, when facing selection pressure, or simply from being separated from others, will become genotypically and phenotypically different from the others. We finally know that different lineages, once separated beyond, say, a species level, generally cannot recombine, and that convergence can only throw separate lineages down parallel tracks; it cannot make them combine*.

*bacteria are sorta-kinda exempt from this rule on account of plasmids. Everything else isn't.

Living birds have scales on their legs and lay dry eggs, which makes it most reasonable to assume that they had reptilian ancestors. They also have an elevated metabolism, just like mammals, and while this has caused some speculation (http://scienceblogs.com/tetrapodzoology/2008/03/the_stem-haematotherm.php#more), it's a dumb idea. The most recent common ancestor of mammals and birds did not have an elevated metabolism; the two groups evolved it separately.

So, which reptiles? In the fossil record there are, after all, a rather lot of reptiles crawling around, stinking up the place. The fossil record is full of holes, and by the Late Jurassic, when archaeopteryx shows up, replete with feathers and flight, there are no earlier, obvious protobird candidates. It simply isn't satisfying to say that archie was the first bird though; it's too well developed, too different from anything else prior for that to be likely. Its feathers are asymmetrical, its wings are huge. Those sorts of traits don't just sprout overnight. Saying that it was just a glider is silly; nevermind the mind-boggling complexities of aerodynamic biomechanics, archie had way, way, way bigger and more developed wings than any modern canopy glider, and furthermore, was living on an island archepelago where there may not have been any trees. It's simply ludicrous to assert that it wasn't capable of powered flight; although it probably wasn't great at it, by modern standards. Birds (and I'm calling archie a bird because that's what convention dictates) had clearly been evolving for some time before archie was around.

This leaves two possibilities; the fossil record forgot to preserve any bird-ancestors, or that the bird ancestors were before the eyes of the paleontologists all along, and they just didn't notice them. The second possibility is more satisfying, and more likely. The sort of small, generalized reptile likely to evolve into birds would simply have been too common to escape fossilization altogether. Futhermore, the sort of fine-grained sediments needed to preserve fine details like feathers are geologically rare, and an early, bird-ancestral reptile might escape detection as such if it wasn't surrounded in a halo of feathers.

So, what's the likely suspect look like? As a general rule; small, generalized animals evolve into more specialized ones. Specialist groups tend to be dead ends, and large animals are usually specialists. We want a small reptile. Birds also share details of the scales, skull, heart and ankle with crocodiles, so whatever the bird ancestor was, it was probably fairly closely related to crocodiles. That still leaves a lot of fossil groups; dinosaurs, rauisuchians, ornithosuchians, simiosaurs, pterosaurs, et cetera. It's pretty much a crap shoot at first glance; pterosaurs were covered in hair or feather like integument, and could fly, but why would a group that evolved complicated membranous wings (http://dinobase.gly.bris.ac.uk/forum/viewtopic.php?id=531) suddenly switch to feathers? Pterosaurs are too specialized to be likely bird ancestors, and they had a few anatomical quirks of their own that birds lack. Simiosaurs had light, birdlike skulls with small teeth and lived in trees (important, since most gliders live in trees as well), but again, they have too many unique traits that birds lack, and their immediate ancestors lack the bird-like traits.

So, using just the Triassic-Jurassic fossil record, you can whittle likely bird ancestors down to dinosaurs, or the crutotarsi, which were some dinosaur-like crocodile relatives, crocodiles, and assorted other archosaurian riffraff.

And, of course, living with the benefits of post 1998 paleontology, we now know that a variety of dinosaurs were wearing feathered coats, but hold the presses; all those dinosaurs with the beautifully preserved feathers come from deposits from after archaeopteryx. Explain that one ya smug Darwinists!

The most plausible explanation is that the lineage of small, two legged, primarily flesh eating dinosaurs called coelurosaurs had been covered in feather the whole time, and the quality of their preservation was such that we just didn't know it. Now, just to forestall any confusion; I'm using "coelurosaur" as a clade, approximately meaning "any animal descended from the last common ancestor of Alex the Parrot and Ornitholestes". The same word had been used to describe all lightweight predatory dinosaurs, but that usage is artificial, and does not describe a clade.

The Coelurosauria includes a lot of animals. Aside from birds, it includes tyrannosaurs (indeed, early Asian tyrannosaurs had feathers, and probably the more familiar late American ones did too), therizinosaurs (http://dino.lm.com/taxa/display.php?name=Therizinosauria) and a lot of other things that you probably wouldn't consider to be particularly birdy. It also includes things like velociraptors, which are manifestly birdy.

The Coelurosauria includes some of the earlier dinosaurs (although none of the earliest), and also some of the very last non-avian dinosaurs. The Coelurosauria does not include the Ornithiscia, a group of dinosaurs who's name means "bird hipped" and which bore beaks. Convergence happens. Scientists mis-name things. Finally, there were plenty of non-avian dinosaurs around at the KT extinction, and scads that didn't contribute to bird evolution in the slightest, including plenty of sauropods, ceratopsids, thyreophorans, and assorted ornithopod riff raff. They were still around for the same reason that apes are still around today; evolution is not necessarily a replacement process.

Microraptor was just what it sounds like; essentially a scaled down velociraptor, and thus not particularly close to being an ancestor of modern birds. It's more like their uncle; a bygone sideline. Although rear-leg airfoils may have been fairly common in ancient birds, they obviously are not now, and neither are teeth, nor bony tails. That's what's wonderful about early bird evolution.

Neornithine, or "modern" birds are obviously quite different from archaeopteryx. They lack teeth. Their skulls have a few less bones as well, particularly in front of the eyes. Thanks to a tendonous pulley, the flight muscles that elevate the wing actually sit below the axis of the wings. They don't have any bones in their tails, excepting a few stumpy ones that anchor their tail feathers.

During the late cretaceous, the final act for most dinosaurs, and indeed most birds, the skies were populated with all sorts of curious intermediates. Particularly, there was one group of birds that lacked the pulley-system of modern birds, but shared, or convergently developed toothless bills and short tails. These are called the enantiornithines (http://en.wikipedia.org/wiki/Enantiornithes), and they were actually quite common. They went extinct at the same time as the dinosaurs for reasons that are by no means clear.

So, while the dinosaur->bird connection is fairly clear, everything else is not. Why did only one group of birds (the neornithines) survive the KT boundry? How diverse were they at the time of the extinction anyhow?

There's reason to believe (http://www.scientificblogging.com/news_releases/the_rocks_versus_clocks_debate_when_did_modern_bir ds_exist)that the most recent living ancestor of all living birds diversified out into all the extant clades of the neornithines sometime in the late cretaceous, which would place it flitting about above the heads of T. rex, triceratops, and sharing the skies with the much more common enantiornithines and the very last of the pterosaurs. Of course, there's also reason to believe that the last common ancestor of all living birds, or at least most living birds, evolved much later than that, say, by ten million years or so. Alas, the fossil record of the paleocene, the period immediately after the extinction of most dinosaurs, just plain sucks, and small, hollow bird bones don't preserve that well anyway.

So the matter is still up in the air, and microraptor is, thankfully, irrelevant to it.

[Big Les]

Neutrino Cannon, you just made my head explode, but I love you for it.

[Round Robin]

[...]Which is what makes the discovery of fossil birds with teeth (http://www.oceansofkansas.com/Hesperornis/martin60.jpg) and feathered dinosaurs (http://dino.lm.com/images/display.php?id=2004)such a head-throbbing embuggerance to it all. All those neat categories fall to pieces, and Nature herself laughs maniacally at our attempts to confine her work to pigeonholes. Nature is vindictive that way.[...]


I just watched the Nova in question last night and had this great thread--and this post in particular--waiting for me. Thanks; and that above quote cracked me up!

[skeptigirl]

Neutrino Cannon, I'll have to read the rest later, but you've started off with a false assumption about what I said. I certainly never said feathers evolved more than once. On the other hand, they could have if the precursors were in the ancestral genes. Fins for example evolved into limbs in marine mammals then back into fins.

[neutrino_cannon]

Neutrino Cannon, I'll have to read the rest later, but you've started off with a false assumption about what I said. I certainly never said feathers evolved more than once. On the other hand, they could have if the precursors were in the ancestral genes. Fins for example evolved into limbs in marine mammals then back into fins.

You asked how many lineages of neornithines made it past the KT boundry. I was clarifying that animals with feather, neornithines, and all other natural clades evolve once. Comparing them to fins is a bit misleading, on a semantic level. Yes, basal tetrapod fins begat therapsid limbs begat mammal legs begat whale and seal fins, but whale and seal fins are not, strictly speaking, the same things. For starters, one is attached to a whale, and the other is part of a seal. They are both modified forelimbs used for propulsion in the water, but there are subtle structural differences, and there's really no reason to think that they represent anything more than convergence.

Everything you said about there being a branch of the neornithines that had already began to diversify after KT is right; although the particulars are not well known at this point, largely due to a crummy paleocene fossil record.

I wouldn't be surprised if many, or even a majority of dinosaurs were covered in some sort of proto-proto feathers though. They were reasonably warm-blooded, it would make sense for them to have some sort of insulation.

[UnrepentantSinner]

Threads like this are why I love this forum. :)

[skeptigirl]

You asked how many lineages of neornithines made it past the KT boundry. I was clarifying that animals with feather, neornithines, and all other natural clades evolve once. Comparing them to fins is a bit misleading, on a semantic level. Yes, basal tetrapod fins begat therapsid limbs begat mammal legs begat whale and seal fins, but whale and seal fins are not, strictly speaking, the same things. For starters, one is attached to a whale, and the other is part of a seal. They are both modified forelimbs used for propulsion in the water, but there are subtle structural differences, and there's really no reason to think that they represent anything more than convergence.

Everything you said about there being a branch of the neornithines that had already began to diversify after KT is right; although the particulars are not well known at this point, largely due to a crummy paleocene fossil record.

I wouldn't be surprised if many, or even a majority of dinosaurs were covered in some sort of proto-proto feathers though. They were reasonably warm-blooded, it would make sense for them to have some sort of insulation.

The question I referred to was where would the neornithines have been at during the KT event. In other words, was it a single species at that time or had the ancestral line already begun to diversify before the KT event. After all, we know it diversified after the event.

As for fins into limbs and back being different than feathers, guess what? There is already experimental evidence you are wrong on that one.

In the Discovery Channel program, Dinosaurs: Return to Life (http://www.discoverychannel.ca/reports/article.aspx?aid=6962) the hypothesis that the genetic instructions remain but are often just switched off was presented. By manipulating chicken embryos with different proteins that would normally trigger the development of a tail, scales in lieu of feathers and forelimbs in lieu of wings, scientists were able to demonstrate that the necessary components for retrograde evolution were still present in the embryo. In other words, scales that became feathers could become scales again. There is no reason to think that feathers could not have evolved, devolved and re-evolved once the genetic mechanisms of development occurred.

[skeptigirl]

Threads like this are why I love this forum. :)Me too.

[neutrino_cannon]

The question I referred to was where would the neornithines have been at during the KT event. In other words, was it a single species at that time or had the ancestral line already begun to diversify before the KT event. After all, we know it diversified after the event.

With all the confusion over the molecular clocks, I think songbirds are the only major group of birds that is widely believed to have diversified long after the KT boundry. There are some fossils from the cretaceous attributed to modern groups of birds; I think it's fairly uncontroversial that shorebirds, seabirds and ratites had already branched by then. What isn't clear now is whether anything else had.

As for fins into limbs and back being different than feathers, guess what? There is already experimental evidence you are wrong on that one.

In the Discovery Channel program, Dinosaurs: Return to Life (http://www.discoverychannel.ca/reports/article.aspx?aid=6962) the hypothesis that the genetic instructions remain but are often just switched off was presented. By manipulating chicken embryos with different proteins that would normally trigger the development of a tail, scales in lieu of feathers and forelimbs in lieu of wings, scientists were able to demonstrate that the necessary components for retrograde evolution were still present in the embryo. In other words, scales that became feathers could become scales again. There is no reason to think that feathers could not have evolved, devolved and re-evolved once the genetic mechanisms of development occurred.

There was also an experiment in making tooth tissues form in embryonic chickens. Assuming that the genes for making something are just "switched off" as opposed to damaged or lost, yes, it's possible for traits to go back and forth like that.

For tetrapod fins though, you're looking at something entirely different. The fins of seals and early tetrapods can be stated, with some certainty not to be the same thing.

There is, for starters, no single gene controlling the "fin-ness" of a limb. Feathers are, as it was explained to me, homologous with scales, and antagonistic to their development. Flip a switch, and you get scaly legs like in a hawk. Flip it back, and you get feathered legs like in an eagle.

With a fin though, you're looking at musculature, and how it's developed and connected. Seal and whale fins don't move in the same way, that's a clue right there. Also, the skeleton is different; early tetrapods had seven fingers, and seals have only five. I doubt that you could get fins by a few genes suddenly reverting to a Devonian condition.

[skeptigirl]

Neutrino you are taking your own wandering from the substance I posted and arguing with yourself.

Let's go back to where this started.

You said, "This is a relative sort of question. Feathers only evolved once".

That doesn't contradict what I posted that you initially misread. I said I wondered how diverse today's bird ancestors were at the time of the KT event.

I said, "So, were there multiple ancestral lines or was there a single 'adam and eve' flock of dinos that went on to be the bird branch of the tree of life? You mistook that to mean ancestral lines outside of the single neornithine ancestral line even though in post #11, I specified all that in great detail complete with references.

Then I suggested features could evolve more than once. Because the mechanism of fins to limbs to fins isn't exactly the same (I'll take your word for it) as from scales to feathers to scales to feathers you then went off arguing that point as if it negated the basic statement I made which was, features can evolve more than once. Even if the example wasn't exact enough of an analogy for you, I cited an additional reference that the genetic blueprint for feathers could be suppressed and later expressed again.

Now you are arguing with yourself that the mechanism for fins evolving twice in marine mammals was new genetic code rather than re-expressed existing genetic code. That's nice, I wouldn't have any idea, I've not looked into it.

I'm happy to read what you have to share on this topic. But just don't do so with the caveat I have gotten something wrong, when you didn't take the time to carefully read what I had posted. If you disagree with something I said, how about addressing the sources I posted in #11 above rather than me. If you think they have something erroneous then by all means let us know.

And yes, the teeth were discussed in the same program I linked to.