note to admins: jazzns invited other people to participate. i'm not sure if i'd like pick up much of this thread, but points have been raised about theropod/avian evolution, which is an interest of mine. i'd like to clear up a misunderstanding or two here.
For instance, in reptile/bird evolution, they note that the furcula (wishbone) is only present in therapod dinosaurs and avian. While that's true, and its certainly something to make note of, lets not get carried away. Why? Because the rest of the anatomy doesn't match up at all. Its a false cladogram, IMO.
in your opinion. shall i list off all the other features known only in birds and theropod dinosaurs? the morphology is strongly homologous.
How did this come about? Probably because no other suitable candidates for avian progenitors exist. Nothing else makes any remote sense.
and this particular idea makes so much sense that even a child can recognize the similarities. take a kid to the museum, show him a t-rex. ask him what the feet look like.
if you actually spend enough time looking at theropod dinosaur skeletons and fossil bird skeletons, and modern bird skeletons, you really begin to lose sight of what's what. i can't even tell you what's a dinosaur-but-not-a-bird, and what's a dinosaur-and-a-bird anymore. because when i see a bird on the hand rail of the stairs on the way to class i think "velociraptor." and when i see a velociraptor i think "bird."
As a result, misinterpretations of anatomy allowed for an over-simplification about convergent evolution.
i'll admit, there is a lot of oversimplification going on here. the path to birds is so incredibly complex and detailed in the fossil record that it's hard to say what exactly happened. and the definitions of "dinosaur" and "bird" are seeming more and more arbitrary to me by the day. for instance, did you know that it's now thought that archaeopteryx was a basal deinonychosaur? it has the hyper-extendible second toe, and every other hallmark of deinonychosaurs. that would mean that dinosaurs like velociraptor evolved from birds like archaeopteryx. and this actually makes a lot of sense, if you look at the skeletons.
and it just gets really complicated when you get into "opposite birds" in the cretaceous. there seems to be a lot of "evo-devo" and convergance going on in the fossil record.
I'm saying you must come to grips with that notion if there is no intermediary between Archy and birds, since Archy was far more bird than he was reptile.
archaeopteryx was a dinosaur. that chicken you had for dinner a few nights ago was also a dinosaur. archaeopteryx isn't really that much more distant from reptiles as any other dinosaur. the first dinosaurs were bipedal, laterally flattened, agile little theropods. the fact that the were bipedal means that they did not require the ground for warmth -- so they were likely warm blooded. since they were warm blooded and small, they likely had a form of insulation: feathers. these are all actually natural and logical steps for ground-dwelling animals. nothing hopeful or monstrous here -- each addition benefits.
what makes archaeopteryx less reptile than say, eoraptor? or coelophysis? the essential differences that make him a bird are really far, far more subtle. in every major way, he is a relatively average dinosaur. and after archaeopteryx, we have a whole slew of intermediates that become more and more bird like. we have enough even that it seems that "birds" as generally accepted in the fossil record, might by polyphyletic (even if today's aren't).
Its not just the wings that presents the problem. We have a completely different pulmonary, integumentary, cardiovascular, etc, system that makes a mountain out of your mole hill. If Archy is indeed an intermediate, he surely must have been an intermediate in between a series of intermediates. There is no way that one day a reptile just popped out Archy, and, voila, the first avian.
that problem is well before archaeopteryx. go raise this objection with the lagosuchids and the earliest theropods. because crocodilian respiration simply does not work with bipedal running (heck, it barely works with crocodilian running). and we know from dinosaurs with pneumatized bones that avian respiration was alive and well on the ground.
no reptile just popped out archie. a dinosaur popped him out. a dinosaur with pneumatic bones, avian repsiration, warm blood, and feathers.
I'm curious to know where to place pterosaurs in the evolution of theropods and avian.
in other words, "nowhere." if you look at birds wings, vs pterosaur wings, they are completely different. theropods (including birds) have three digits, pterosaurs have the standard five. in birds, the wing is formed by a fusing of those three digits into a carpometacarpus, and the wing is made from feathers. in pterosaurs, the leading edge of the entire flying surface is a single elongated digit.
see, theropods and birds:
Especially when considering that the majority of theropods stood well over 10 feet tall, while Archy is about the size of a chicken.
entirely not true. the vast majority of theropods found have been rather small, light, and fast ones. from the earliest days of the dinosaurs, that has been the theropod model. coelphysis, and compsagnathus, and eoraptor. deinonychus and velociraptor and troodon. and archaeopteryx. you're just more familiar with the big guys because they sell more museum and movie tickets -- t. rex (which was a truly unusual dinosaur), allosaurus, megalosaurus, etc. the smaller ones are the ones we see all the advancements in, too. the first feathers, etc. even in various lineages, it seems they all started with smaller ancestors. tyrannosaurids even started small.
Kind of strange that a megalithic-sized creature could, by happenstance, produce such diminutive progeny. I realize that some classified theropods are of small stature, but we see those earlier in geologic record.
no, we have them all the way through the cretaceous. we just tend to call the cretaceous ones (and everything after) "birds."
But where does it leave Pterosaurs which are said to have existed in the late Triassic period? It seems that flight has come about much longer than avian have been around, according to evolution. I'm curious to gather your input.
winged insects were around in the pennsylvanian, some 40 million years before either of them. it easy to mistake pterosaurs for birds, i guess, because they're both archosaurian sauropsids. but really, to anyone who knows what they're talking about, your argument makes about as much sense as "where do insects fit in?"
For a forelimb in a distant relative to become a fully functional wing in a preceding generation, there surely would have to have been innumerable gradations in between.
you are aware of the fact that, according to bone structure, birds only developed bony wings quite recently? most of the cretaceous and tertiary birds have fully-formed hands. the essential difference is that in a wing -- a carpometacarpus -- the digits are fused. in hands, they are free. some birds today are even still born with free digits.
the wing, in terms of flight surface, is made of feathers. where would you like to see the transition? theropod arm-length shows the trend adequately enough.
But more simply, you can't hang it all up on by looking at the feet of theropods because their feet are similar.
it's not simply the feet. a bird's entire skeleton is perfectly homologous to a theropod dinosaur's skeleton. to argue that they are not related is to argue for convergent evolution to the point of miracle. it's like getting caught plagiarizing on your bio term paper, and arguing to your professor that even though your essay is word-for-word exactly the same as your source (except for a few synonyms), you didn't actually copy it. it's just coincidence that you and some well known biologist wrote exactly the same paper, and yours is all original material.
the response from the professor would be "yeah, right. you fail."
Dodson isn't alone in the criticism. Alan Feduccia, a leading ornithologist, routinely asserts that there are many problems in the theory,
i've never heard of dobson, but if anyone could be considered the "laughing stock of paleontology" it's alan feduccia. i'm serious -- go find a paleontology newsgroup, mention his name, and watch yourself get laughed off the board. he's a nut, a crackpot, and someone who knows absolutely nothing about biology outside of birds, and next to nothing about paleontology. paleontolgists like to say to him "that's great; you study birds. so do i. in fact, i study everything you study, plus an additional 120 million years worth of information."
but perhaps you should look up feduccia's claims -- even he cannot deny that maniraptorian dinosaurs are basically primitive flightless birds. he contends that things like velociraptor mongoliensis aren't, in fact, dinosaurs. let me put this another way. to feduccia, the connection between archaeopteryx, theropod dinosaurs, and modern birds is more obvious than the connection between theropod dinosaurs and every other dinosaur, like sauropods, or ornithsticians. that's really how obvious this connection is: even the cranks accept it, and have to twist data on the other end to support their ideas.
Well, lets go over this because there are quite a few discontinuities. You say they are ground dwelling, which obviously means they are runners. If so, then what selective advantage feathers would have for running underneath the canopy of trees?
there's some debate about ground-up vs. trees-down. but frankly, animals like the velociraptor i mentioned above hunt with their feet. they would jump onto their prey, and use their claws to precisely puncture important arteries in ceratopsians. as a jumping predator, even a little bit of lift is an easily selectable adaptation. it's not full-on-flight, or bust.
there are also a number of other features that come part and parcel with feathers -- warmth, and sexual displays.
Feathers create an awful lot of drag on the ground.
tell that to a ratite. and really -- wouldn't drag be more of a concern in the air?
But mammalian hair is far less costly and easier to facilitate heat than feathers
the earliest feathers were (essentially) hair.
which Feduccia says is uniquely optimal for flight.
feduccia has apparently never heard of our other flying archosaurs, the pterosaurs, which did not have feathers (they had mammalian-like hair). the largest animal to ever fly was the queztalcoatlus -- a pterosaur. you ever seen a bird with a 40-60 foot wingspan? "optimal" my ass.
That's not the problem. The problem is that Crocodiles are placed before birds on the chain.
no, "crocodilians." not modern crocodiles. crocodiles very much like modern crocs were around in the mesozoic, but the paleozoic ones, i promise, were quite different. the family that crocodiles comes from diverges slightly lower than dinosaurs, but very close to the same time. birds diverge from dinosaurs.
if you think that's counter-intuitive, mammals diverge slightly lower than reptiles.
If that's the case, then when did they diverge, since the bones of avian are hollow?
pneumatized (hollow) bones are first seen in ground-based theropod dinosaurs -- the only other archosaurs they're seen in are pterosaurs, and then only in the wings (which are not homologous -- it's convergent, because light bones makes sense).
Where exactly do beaks, which is cartilaginous, btw, come in?
beaks are made of a horny keratin bill over bone. where do they come in? glad you asked -- dinosaurs. oviraptors have beaks, and all ceratopsians have beaks. (oviraptors are homologous, ceratopsians are not.) the important point about beaks being made of keratin is that feathers are made of keratin.
When did the vascular system completely alter? When did the pulmonary system completely alter?
i should point out that i was mistaken above. that's what i get for firing off posts late at night, without thinking too clearly. crocodilian respiration does work on two legs; in fact, it works better on two legs. it's a not-so-well-known fact that crocodiles won't chase prey (or threats) on land. they are ambush-predators, and can't maintain speed for a long time. part of that is due to their respiration. because they are rib-breathers, their side-to-side gait means that they cannot breath while running.
the up-and-down gait of a dinosaur means that they can, and the motion actually helps respiration.
the change from a one-stroke to two-stroke respiration system appears to have happened in stages, first with the development of air-sacs (which function like a diaphragm in some modern lizards) in theropod dinosaurs, and then with an extension of the bronchial tubes. you may be interested in this post and this post of mine, from two years ago. you'll find the thread ended shortly after those posts.
For every superficial similarity that exists between theropods and avian, there are vast differences in the far more important inner-contrivances of each specie.
i think "superficial" and "vast" are arbitrarily defined by you. for instance, the fact that theropod dinosaurs and birds are the only two groups of animals ever discovered that use their bones as part of their respiratory system. "superficial" similarity, right? dinosaurs have rear-facing halluxes, birds have them opposed. "vast" difference, right?
how about this. you name something about birds, and i'll name the dinosaur that has it.
The weakness of such an argument, focusing on the fact that both theropod's and avian have tridactyl forelimbs, is not nearly enough to suggest ancestry.
no, that was not the argument. the argument was that theropod and avian limbs -- which happen to be homologous -- are very obviously different then pterosaur wings. they don't even have the same number of fingers, and the structure is entirely different. basically, "pterosaurs aren't birds" was the point.
the homology of theropod and avian limbs is well known. some birds are even still born with nearly intact theropod hands -- a point creationists like to try to play to their advantage. the similarity isn't superficial. they are the same. and even so, the carpometacrapus is a recent development. by far, most post-cretaceous birds fond lack it -- they have diminutive, exagerated dinosaurian hands.
Why? Because not only is that completely subjective, but its cherry picking superficial similarities when it ignores much larger and neccessary ones in order to support the theory.
which larger and neccessary (dis)similarities? it seems that every time you bring up something that's "different," and i say "sorry, dinosaurian feature" or "exactly homologous to a dinosaurian feature." you write it off as trivial. you know what? it really is entirely trivial -- birds are dinosaurs. the differences are so minute that they simply do not matter. find me something that's not trivial, and actually is different:
But, if we were to focus on such a similarity, we should also note the difference in the number of digits between birds and dinosaurs. Where did this disparity come from if they are in fact so similar?
That is besides the fact that feduccia still recognizes that birds evolved from thecodontia. So NJ is using the authority of someone who is simply arguing that birds evolved differently, not that they didn't evolve.
what the hell is feduccia arguing, anyways? does he even know anymore?