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Author Topic:   Theropods and Birds showing a change in kinds
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 46 of 150 (544890)
01-29-2010 6:19 AM
Reply to: Message 38 by slevesque
01-29-2010 2:33 AM


Feathers as novel features
The issue, for my part at least, I can't speak for every creationists out there, is if there is any evidence of the transitional phases between scales and feathers. Both are very different both on the surface and at the microcospic level I believe, and this type of evidence would be much more compelling for me then a dinosaur with complete feathers.
It is true that scales and feathers are very different structures, and this is why most people who study this don't believe that feathers evolved from scales.
There is evidence, however, of the type of structure feathers are believed to have evolved from, and Sinosauropteryx is one of the dinosaurs we find it in. The ginger structures being discussed aren't true feathers - they lack the barbs, barbules and hooklets of real feathers, which are only found in birds and maniraptoran dinosaurs so far (Sinosauropteryx is a compsognathid, a different type of theropod). These are much simpler, hollow filaments, which were probably the ancestors of true feathers.

This message is a reply to:
 Message 38 by slevesque, posted 01-29-2010 2:33 AM slevesque has replied

Replies to this message:
 Message 51 by slevesque, posted 01-29-2010 4:07 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 63 of 150 (545312)
02-03-2010 5:22 AM
Reply to: Message 51 by slevesque
01-29-2010 4:07 PM


Re: Feathers as novel features
quote:
Ok, but don't these 'ginger structures' come from a previous structure in therapods ? If this wasn't scales, what was it ?
Good question, and one I'm not sure I'm qualified to answer. Thing is, they might not have needed much of a previous structure to come from. Before any of these structures were discovered in theropods, Richard Prum, one of the world's experts on feathers, had proposed a model of feather evolution based on how they developed in the embryology of modern birds. What he predicted as 'Stage 1' in this evolution was an undifferentiated, hollow cylinder of beta-keratin. That is pretty much what we seem to have discovered in theropods. The question then becomes, how much of an ancestral structure do you need in order to evolve hollow, undifferentiated filaments of a protein already present in your skin? It could be that only a small genetic change was needed to produce these things, and once there they worked as rudimentary insulation until they could be refined for display purposes and, later, flight (I'm guessing here, though).
After much rummaging, I finally managed to find an open-access copy of Prum's 1999 article - Development and Evolutionary Origin of Feathers (JOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 285:291—306 (1999)). I haven't had time to read it yet, but I'll have a look and see if I can get back to you with more details.
-----------------------------------------------------------------------
You mentioned in another post that birds have been around longer then theropods, but this isn't right. The earliest theoropd we've found may be Eoraptor, which is from rocks between the border of the Middle and Late Triassic, right back at the times of the earliest dinosaurs. Not everyone agrees this is a theropod, with some arguing it's a more primitive dinosaur. By the end of the Triassic, though, we have dinosaurs like the Coelophysoids, which everybody agrees are theropods. The oldest Coelophysoid we've found so far comes from the late Triassic of New Mexico, estimated at about 215 million years ago.
The oldest birds we've discovered are still, as far as I can tell, Archaeopteryx and others from about the same time period. These all come from the late Jurassic, more than 50 million years after the early coelophysoids. Nothing's been discovered to suggest that birds predate theropod dinosaurs yet.

This message is a reply to:
 Message 51 by slevesque, posted 01-29-2010 4:07 PM slevesque has replied

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 Message 64 by RAZD, posted 02-03-2010 7:41 AM caffeine has not replied
 Message 67 by slevesque, posted 02-03-2010 3:10 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 77 of 150 (545542)
02-04-2010 7:19 AM
Reply to: Message 67 by slevesque
02-03-2010 3:10 PM


Re: Feathers as novel features
I think the main logic in his discours is this: if feathers are so perfectly optimized for flight, why would anyone suggest they in fact evolved for endothermy (for which they are a sub-optimal structure, both in efficiency and in production cost)
Not all feathers are optimised for flight, though. There are a plethora of different types of feather - different species have different feathers, and the same species have different feathers on different parts of their body and at different stages in their life. Only a minority of these are the asymmetrical, pennaceous feathers perfectly suited for flight. Most birds begin life covered with fluffed-up downy feathers which aren't at all aerodynamic, but trap air quite well to insulate the little baby bird.
All the functions which people suggest as the ancestral functions of feathers - display, insulation, water resistance etc., are all performed by feathers in modern birds. What's more, if we're thinking evolutionarily, the ancestors of feathers must have been simpler than their current forms - it's silly to suggest the incredibly complex feathers in the tail of a falcon could have sprung up out of nothing. You can simplify the design of a feather considerably, right down to the basic sort of filaments we're looking at in dinosaurs like Sinosauropteryx, and still be left with something that might work as an imperfect insulator, or that could be used for sexual displays. What you're not left with is much of a flight feather.
[qs]I had this information from prof. John Ruben of OSU (who was involved in the previous research who held that birds do not descend from dinosaurs):[qs] Okay, I found the same quote in this article. He doesn't, however, back up the claim anywhere I can find, and despite all my rummaging on the internet, nowhere can I find mention anywhere of a Triassic bird fossil. This includes all the articles I looked at by and about the OSU researchers - were there really such support for this claim, I think they might have mentioned it.
It's possible that he means birds appear in the fossil record before maniraptoran theropods, which are the specific clade of theropods birds are supposed to have evolved from. These are the dinosaurs in which we find true, indisputable feathers; and some of which may have been able to fly (artist's impression from wikipedia below just because I like it).
Let's be clear what's being said here though. Most biologist believe birds to be maniraptoran, coelurosaurian theropods. The earliest fossil theropods predate birds in the fossil record by at least 60 million years. The earliest known coelurosaurian theropod, Eshanosaurus, dates from about 196 million years ago - almost 50 million years before Archaeopteryx. Some dispute that this is really a coelurosaur, and the earliest unquestioned examples come from about the same time or just a bit before Archaeopteryx. Thing is, by this time they're already quite diverse, so they must have already been around for a while.
Even if we discount all the possible but dubious coelurosaurian and maniraptoran fossils that predate Archaeopteryx, we have a huge variety appearing alongside the birds in the late Jurassic and early Cretaceous. If we reject their common theropod ancestor, then we're forced to argue instead that a structure as complex as the feather evolved not just once, but twice, in basically the same form, at about the same time. This stretches credulity a bit.
To RAZD: I'll get back to you, still working on understanding feather follicles.

This message is a reply to:
 Message 67 by slevesque, posted 02-03-2010 3:10 PM slevesque has replied

Replies to this message:
 Message 90 by slevesque, posted 02-04-2010 3:40 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 106 of 150 (545780)
02-05-2010 9:49 AM
Reply to: Message 90 by slevesque
02-04-2010 3:40 PM


Re: Feathers as novel features
Ever seen baby ostriches covered with downy feathers ? Quite cute right, but now imagine it getting all wet. It will die of hypothermia within minutes if it's mother doesn't heat it up. For a species to be covered by such a structure for endothermy would be extremely maladaptive, to the point of being harmful.
Assuming that this is the case, it might imply merely that plumulaceous, downy feathers were evolved for thermoregulation in a low-humidity environment when getting wet was rarely a problem. Also, simple observation seems to suggest that feathers can't be that poor at insulation. Despite maintaining higher inner temperatures than mammals, even small birds seem to have little problem surviving at the highest latitudes. Snow petrels happily breed right at the sorth pole, and they're less than half a metre long.
And of course, no dinosaurs are found with downy feathers. They are either found with 'dinofuzz' or with true feathers which have a central rachis, etc.
Many dinosaurs have been found with downy feathers — all oviraptoriformes seem to have possessed at least some, and there’s a new taxon reported in Nature last year which not only seems to have possessed downy feathers, but also appears to be a maniraptoran theropod from before Archaeopteryx. (Incidentally, does anyone have access to Nature so that we can confirm this article says what I think it says?).
In fact, the dinofuzz is found not only on therapods, but also on icthyosaurs, pterosaurs and ornithischian dinosaurs. In none of these cases are they related to feathers, and there is nothing to suggest then that this should be the case with therapods.
There is indeed something to link these structures to feathers. Unlike other epidermal coverings, feathers are composed almost entirely of beta-keratins. When the 'dinofuzz' filaments of the theropod Shuvuuia were examined to determine their makeup, it was discovered that, they too, are composed almost entirely of beta-keratins (Schweitzer, M. H. 2001. Evolutionary implications of possible protofeather structures associated with a specimen of Shuvuuia deserti. In Gauthier, J. & Gall, L. F. (eds) New prespectives on the origin and early evolution of birds: proceedings of the international symposium in honor of John H. Ostrom. Peabody Museum of Natural History, Yale University (New Haven), pp. 181-192. - found on Tetrapod Zoology ). One more coincidence if these are believed to be non-homologous structures.
If it turns out that the possible filaments found in ornithischian dinosaurs and pterosaurs are, in fact, the same things as found in theropods, this might simply suggest that beta-keratin filaments are a primitive ornithodiran* trait, originally evolved for insulation and/or display. In this model, it would be the later specialisation of these structures into true feathers in theropod dinosaurs that paved the way for the great evolutionary radiation of birds.
*My new word for the day. Ornithodira is the clade that unites dinosaurs and pterosaurs.
I couldn't tell you. Contacting him directly to ask him might be the onl way of knowing what he meant.
Until we find any support for the claim I'll stop saying it
Okay — to clarify though, everybody agrees that theropods appear in the fossil record long before birds. What’s a matter for dispute still is whether the specific type of theropod birds are believed to have evolved from appear before them.
Convergent evolution can do marvels. Exactly the same sonar structure up down to the genome level in dolphins and bats, for example.
As pointed out upthread - this isn't really true. Bats and dolphins have quite distinct sonar structures. All that's been discovered is that one gene involved in sonar seems to possess the same mutations in the two different animals.
Edited by caffeine, : No reason given.

This message is a reply to:
 Message 90 by slevesque, posted 02-04-2010 3:40 PM slevesque has replied

Replies to this message:
 Message 110 by Dr Adequate, posted 02-05-2010 12:58 PM caffeine has not replied
 Message 123 by slevesque, posted 02-05-2010 5:11 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 107 of 150 (545782)
02-05-2010 9:56 AM
Reply to: Message 102 by Dr Adequate
02-04-2010 9:43 PM


Phylogenetic nitpick
A coelurosaur such as Compsognathus is much closer anatomically to Archaeopteryx than it is to another theropod dinosaur --- T. rex, for example. And Archaeopteryx is much closer anatomically to Compsognathus than it is to, for example, a sparrow (or any other living bird, for that matter).
Tyrannosaurs are coelurosaurs, just slightly more distantly related to birds than compsognathids. A better example would be comparing archaeopteryx to paravian dinosaurs like Velociraptor or Dromaeosaurus; compared with a more distant theropod like Allosaurus.

This message is a reply to:
 Message 102 by Dr Adequate, posted 02-04-2010 9:43 PM Dr Adequate has replied

Replies to this message:
 Message 109 by Dr Adequate, posted 02-05-2010 12:21 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 135 of 150 (545911)
02-06-2010 9:26 AM
Reply to: Message 109 by Dr Adequate
02-05-2010 12:21 PM


Re: Phylogenetic nitpick
=True ... and yet doesn't that make my point even pointier? Which really looks like the odd one out --- Tyrannosaurus, Compsognathus, Archaeopteryx? I have to go with Tyrannosaurus.
So I guess what I should have said is: "A maniraptor such as Compsognathus is much closer anatomically to Archaeopteryx than it is to another coelurosaur --- T. rex, for example."
Wasn't pointing out a problem with your point, just being pedantic with the terminology. To continue a little bit further in that vein, Compsognathus isn't a maniraptoran. Here's the modern understanding of coelurosaur phylogeny (based on Senter (2007), from the wiki page on Coelurosauria:
------Tyrannosauroidea
     |
     |
-----        ------Compsognathidae
     |      |
     |      |
      ------        ------Ornithomimosauria
            |      |
            |      |
             ------
                   |
                   |
                    ------Maniraptora
Your link isn't working for me --- are we thinking of the same article? "A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus"?
Yes, Anchiornis is a pre-Archaeopteryx maniraptor.
Yes, sorry for buggering up the link. I can see this from the abstract, but I was trying to check whether the article claimed that there were preserved impressions of plumulaceous feathers, as google seemed to imply, contra slevesque's claim that no dinosaurs had downy feathers.
Edited by caffeine, : formatting messing up my diagram
Edited by Admin, : Add code dBCode.
Edited by Admin, : Improve diagram.

This message is a reply to:
 Message 109 by Dr Adequate, posted 02-05-2010 12:21 PM Dr Adequate has replied

Replies to this message:
 Message 136 by Dr Adequate, posted 02-06-2010 9:12 PM caffeine has replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 139 of 150 (546070)
02-08-2010 4:36 AM
Reply to: Message 136 by Dr Adequate
02-06-2010 9:12 PM


Re: Phylogenetic nitpick
Well it seems like I was speaking as if things are a lot more resolved than they reall are. From UCMP's page on Coelurosauria:
quote:
At this point they (Compsognathus and Ornitholestes) are considered incertae sedis; in other words, we know that they are theropods; and probably coelurosaurs; but we don't know who they are related to or how they fit into the big picture of theropod phylogeny.

This message is a reply to:
 Message 136 by Dr Adequate, posted 02-06-2010 9:12 PM Dr Adequate has not replied

  
caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 140 of 150 (546072)
02-08-2010 5:20 AM
Reply to: Message 123 by slevesque
02-05-2010 5:11 PM


Re: Feathers as novel features
The point is that at one point along the lineage the dinosaurs had only down feathers. Assuming that they evolved in a low-humidity environment is cool, but there isn't a lot of those isn't it. Care to give an example of such an environment ? Because it sounds to me the only place this would fit would be the desert.
There were more deserts in the Late Triassic and Early Jurassic than there are now, as a result of the big supercontinent leaving many regions a long way from the sea. These areas would also be subject to great temperature swings, and a trapped layer of air helps the body to not heat up too quickly in the day as well as not cool down too fast at night. A little bit of reading about down insulation on the web seems to suggest that you're right about it being pretty useless when wet. The consensus also seems to be that it's pretty much the supreme insulator when dry, however.
I can't access the link, but it's important not to mix up down feathers and 'dinofuzz'.
Sorry about the link - this one should work. And don't worry, I'm not getting feathers confused with simpler filaments. From the abstract:
quote:
Furthermore, the extensive feathering of this specimen, particularly the attachment of long pennaceous feathers to the pes, sheds new light on the early evolution of feathers and demonstrates the complex distribution of skeletal and integumentary features close to the dinosaur—bird transition.
This only mentions pennaceous feathers, contour feathers like flight feathers; not the plumulaceous downy ones, but the body of the article seems to talk about these as well. This dinosaur is hardly unique though. Here's the discussion of Caudipteryx and Protoarchaeopteryx from an open-access journal that we can all read:
Two feathered dinosaurs from northeastern China
quote:
Wherever preservation made it possible, we found semi-plumes and downlike feathers around the periphery of the bodies, suggesting that most of the bodies were feather-covered, possibly like Archaeopteryx. Feathers found with Otogornis were also apparently plumulaceous. Plumulaceous and downy feathers cover the bodies of Protarchaeopteryx and Caudipteryx, and possibly that of Sinosauropteryx as well. This suggests that the original function of feathers was insulation.
Isn't beta-keratin a pretty common thing ? (My bio classes are far right now lol)
Reptiles scales contain beta-keratins too, but they're also constructed partly from alpha-keratins. In modern animals, bird feathers are unique in being composed almost entirely of beta-keratin, and this is something they seem to share with the filaments of Shuvuuia.
Edited by caffeine, : tags and typos

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 Message 123 by slevesque, posted 02-05-2010 5:11 PM slevesque has not replied

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