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Author Topic:   Archaeopteryx and Dino-Bird Evolution
Mallon
Inactive Member


Message 37 of 200 (286937)
02-15-2006 1:37 PM
Reply to: Message 36 by arachnophilia
01-18-2006 9:40 PM


Ugh!
I wouldn't put too much faith in anything Horner says -- especially as it pertains to T. rex.
And just to add/clafify to some things said earlier in this thread...
- Cladistically speaking, humans are NOT classified as reptiles. We are derived from synapsids (the primitive ones informally known as "mammal-like reptiles"), essentially the sister clade to "reptiles".
- Interesting to note that some dinosaurs (oviraptorids, specifically -- Nomingia, more specifically) had pygostyles.
- It has been argued numerous times now that dromaeosaurids ("raptors") are, in fact, secondarily flightless birds, due to their being more bird-like than Archaeopteryx in some ways.
Just some food for thought.

This message is a reply to:
 Message 36 by arachnophilia, posted 01-18-2006 9:40 PM arachnophilia has replied

Replies to this message:
 Message 38 by Coragyps, posted 02-15-2006 1:41 PM Mallon has not replied
 Message 40 by arachnophilia, posted 02-15-2006 10:26 PM Mallon has replied

  
Mallon
Inactive Member


Message 41 of 200 (287228)
02-16-2006 8:30 AM
Reply to: Message 40 by arachnophilia
02-15-2006 10:26 PM


Re: Ugh!
quote:
well, yes. but the synapsid were reptiles at the time.
They were 'reptiles' under traditional Linnaean classification, which went out of style twenty years ago. The more highly derived "pelycosaurs" were already quite different from other typical reptiles.
quote:
where do we put dinosaurs? are theropod dinosaurs birds, or vice versa?
Birds are definitely theropod dinosaurs, but not all theropod dinosaurs are birds.
quote:
i don't know if i would call velociraptor or dienonychus a flightless bird. i'm also not sure how they are "more bird-like than archaeopteryx" either.
For one thing, Velociraptor has uncinate processes -- a very birdlike feature (though seen in other reptiles as well). Other aspects of the pectoral girdle suggest bird affinities as well. Read any of Greg Paul's two books to learn more. He's the one pushing hardest on this front lately.
quote:
the problem is that it's not just the theropod dinosaurs that have scutes, either. anklysaurs had them. which means that the genetic code for feathers existed before the saurischia/ornithischia divide.
I really don't think that bird 'scutes' (i.e. scutellate tarsi) are at all homologous to the bony scutes in ankylosaur skin, so I don't know how far that argument will get you.
quote:
longisquama is a curious reptile (archosaur? ... ?) that appears to have feathers
I think you'll have a hard time arguing that those structures on Longisquama are real feathers if you look at them in detail. Some have even suggested they're just preserved fern fronds.

This message is a reply to:
 Message 40 by arachnophilia, posted 02-15-2006 10:26 PM arachnophilia has replied

Replies to this message:
 Message 42 by arachnophilia, posted 02-16-2006 9:53 PM Mallon has replied

  
Mallon
Inactive Member


Message 43 of 200 (287562)
02-17-2006 8:49 AM
Reply to: Message 42 by arachnophilia
02-16-2006 9:53 PM


Re: Ugh!
quote:
quite -- i just don't think we can go dashing off calling all theropods "birds" willy-nilly.
I completely agree. But I don't know of anyone who is refering to some theropods as flightless birds without good reason. Note that I don't necessarily subscribe to this idea; just playing devil's advocate.
quote:
the primary feature i look for in calling something "bird" is the clawless, fused digits of a bird wing.
Very well. That's still very much a subjective choice, as I'm sure you will agree. Other scientists might chose another apomorphy by which to identify birds. Still others would rather describe birds based on their relationships to other groups (i.e. stem- or node-based definitions).
quote:
but if it's a feather, it's still kind of strange.
There has certain been much literature on the issue. For the pros, see:
Jones, T.D., J.A. Ruben, L.D. Martin, E.N. Kurochkin, A. Feduccia, P.F.A. Maderson, W.J. Hillenius, N.R. Geist, and V. Alifanov. 2000.
Nonavian feathers in a Late Triassic archosaur. Science 288: 2202-5.
The cons:
R.R. Reisz, H.-D. Sues. The "feathers" of Longisquama. Nature 408:428.
As far as I'm concerned, even if the 'feathers' of Longisquama and birds were one and the same (which I don't think they are), the rest of the skeleton just doesn't compare at all between the two. Longisquama definitely isn't a contender, at least as far as bird ancestry is concerned (which I know isn't what you're contending, arachnophilia).

This message is a reply to:
 Message 42 by arachnophilia, posted 02-16-2006 9:53 PM arachnophilia has replied

Replies to this message:
 Message 44 by arachnophilia, posted 02-21-2006 1:28 AM Mallon has replied

  
Mallon
Inactive Member


Message 45 of 200 (289124)
02-21-2006 11:34 AM
Reply to: Message 44 by arachnophilia
02-21-2006 1:28 AM


Re: more on longisquama
quote:
as it stands, i think i will still contend that birds and dromeosaurids share a common ancestor, but are not closely related enough to put in the same clasification as "birds." the dromeosaurid line did not produce modern birds, if memory serves.
You're right in saying the dromaeosaurid line did not produce birds. It is commonly argued that the deinonychosaurs (dromaeosaurids + troodontids) are the sister taxon to the birds.
But maybe after reading Paul's book, you will change your mind. That book is terribly out of date, mind you. I'm just impressed that you were able to pick up PDW at a used book store -- that thing is very hard to come by.
quote:
from what i've heard, feduccia's theories are not well regarded in the paleontology community. i've heard some even claim that he is intellectually dishonest, or that he is ignorant of dinosaurian biology and anatomy.
Is it any wonder creationists continually cite him for support?
quote:
he alleges that birds evolved from other thecodonts, not theropod dinosaurs, and that the dromeosaurid likeness is just convergant evolution.
I think he has even changed his tune now and argues that neither birds NOR deinonychosaurs are theropods, but evolved instead from a drepanosaurid-like ancestor. There was a paper on this recently...
quote:
unfortunately, i can't get the article at just this second
If memory serves me, the Reisz paper is available on his lab website for download.

This message is a reply to:
 Message 44 by arachnophilia, posted 02-21-2006 1:28 AM arachnophilia has replied

Replies to this message:
 Message 46 by arachnophilia, posted 02-21-2006 6:52 PM Mallon has replied
 Message 48 by arachnophilia, posted 02-21-2006 7:12 PM Mallon has not replied
 Message 54 by arachnophilia, posted 02-22-2006 9:07 PM Mallon has replied

  
Mallon
Inactive Member


Message 47 of 200 (289337)
02-21-2006 7:01 PM
Reply to: Message 46 by arachnophilia
02-21-2006 6:52 PM


Re: drepanosaurs? is feduccia nuts?
quote:
ok, that just makes my brain hurt. how are deinonychosaurs NOT theropods?
If you ever find out, let me know! The answer is beyond fathom.

This message is a reply to:
 Message 46 by arachnophilia, posted 02-21-2006 6:52 PM arachnophilia has not replied

  
Mallon
Inactive Member


Message 57 of 200 (289733)
02-23-2006 9:41 AM
Reply to: Message 54 by arachnophilia
02-22-2006 9:07 PM


Re: speaking of velociraptors
quote:
now, i don't mean to call you on this to be rude or anything
It's not rude at all. I always appreciate it when someone points out my mistakes. I invite it on my site.
quote:
a recent study showed that velociraptor claws would have been poor slicing blades.
Yes, I'm familiar with the study. Just haven't really had the chance to update it on my website. In fact, to be honest, I forgot that I had written anything that implied the contrary of the study's findings. There's probably lots more on my site that is out of date (including my bio). I need to do a major content update.
Otherwise, I agree with everything you say. Except the bit out Velociraptor having brightly coloured feathers to get the prey's attention. If you're a predator, I think the last thing you want to do is to get your prey's attention (that's what made those WWD shows such a tragedy -- the big theropods would run up to their prey, roaring all the while and scaring them away).

This message is a reply to:
 Message 54 by arachnophilia, posted 02-22-2006 9:07 PM arachnophilia has replied

Replies to this message:
 Message 58 by arachnophilia, posted 02-23-2006 3:52 PM Mallon has not replied

  
Mallon
Inactive Member


Message 62 of 200 (289902)
02-23-2006 8:43 PM
Reply to: Message 61 by DBlevins
02-23-2006 5:27 PM


Re: Question for Arach or anyone
Yes, most do, I believe.

This message is a reply to:
 Message 61 by DBlevins, posted 02-23-2006 5:27 PM DBlevins has not replied

  
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