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Re: Re: propaganda of the majority



>
>>Actually, it was Ostrom who proposed the "insect net" theory, and he has
>>never strongly endorsed it.  He just wanted to get yet another idea out
>>there for people to consider.
>
>What do you make of this "insect net theory". Do you find it plausible?
>Can you suggest any other evolutionary advantage other than insect
>capture which would lead to the evolution of flight feathers in a 
>cursorial biped?
>

Proto-flight feathers might aid a predator which pounces on its prey.

>---
>>[Padian quote deleted]
>>These comments miss the main argument of the cursorial hypothesis: the fact
>>the birds alone among flying/gliding vertebrates have forelimbs highly
>>transformed for flight, but hindlimbs still wholly adapted for terrestrial
>>locomotion.  Bats, pterosaurs, flying lizards, flying frogs, flying
>>"lemurs", etc., all have wing/patagia on their hindlimbs, whereas birds
>>(including Archaeopteryx) have fully erect legs.
>
>I don't find this convincing evidence for a cursorial hypothesis. For one 
>thing, bipedalism and occupying the same niches could lead to convergent 
>forms in the hindlimbs of birds and late Cretaceous theropods. 

(the Spectre of Seeley rises again)
Actually, the hindlimbs of birds resemble those of Late Triassic to Late
Cretaceous theropods.  Also, I wouldn't think that birds and theropods
shared niches.  In any case, it might have been more accurate for me to say
that the hindlimbs of birds supported the bipedal ancestry of birds, since
it could be argued that birds descended from arboreal bipeds.  However, the
evidence argues strongly against birds being descended from arboreal
quadrupeds, as all known flying/gliding vertebrates descended from those use
the hindlimb in the "wing" strucgture.

>
>---
>>>With respect to the dinosaurian origin of birds, Feduccia says:
>>>
>>>"If Archaeopteryx lived in trees, it means that it evolved not from
>>>dinosaurs as most paleontologists currently believe, but from some
>>>tree-dwelling reptile, since dinosaurs lived on land and not in trees".
>
>>It's good to know that Alan knows the whole of dinosaurian diversity, since
>>those of us who work on them still find strange new morphotypes every few
>>years :-)
>
>I think Alan's point here is that there are no documented arboreal
>characters in theropods in the fossil record (other than possibly those 
>of Archaeopteryx if you call it a theropod). Kevin Padian AGREES with 
>Alan on this point. Has anyone documented some arboreal theropod
>characters recently? What leads you to believe Greg Paul may be right
>about small theropods being arboreal?

See discussions elsewhere (including below) on dromaeosaurid foot adaptations.

>
>---
>
>>Hmmm...You might tell me...Do you...ahem...cling onto any study that
>>supports the arboreal hypothesis, even if it is inadequate? :-)
>
>I try not to cling to anything if it's inadequate :-)
>(nice touche' though)
>---
>
>>Actually, Phil Currie is working on sme of these ideas.  An important point
>>with the last comment - Archie's tail is similary rigid, best seen in the
>>newest specimen.  If the rigid tail of dromaeosaurids is reason to reject
>>their arboreality, than it should reject it for Archie.
>
>Aren't dromaeosaurids physically larger than Archie? Presumably, the larger
>the creature the more difficulty it would have maneuvering in the trees with
>a stiff tail. Besides, the rigid tail of dromaeosaurids is not in itself
>a reason to reject their arboreality, it's only one factor. In contrast to
>Archie, dromaeosaurids lack flight feathers, sharp toeclaws that most 
>closely resemble those of modern perching birds(Feduccia), and semi-erect 
>posture (unless Martin's reconstruction is flawed). The reason to reject 
>dromaeosaur arboreality is the lack of _any_ arboreal characters. 

I wouldn't go that far, and in fact the more I look at it, the less I'm
convinced that small maniraptorans can be kept out of the trees (after all,
jaguars and leopards are very good climbers, and are heavier than almost all
dromaeosaurids).  Dromaeosaurids like Velociraptor are fairly small
(probably jackal-coyote mass), and so weight wouldn't be that much of a
deterrent. The data isn't in on how much dromaeosaurid toe claws look like
perching birds, as Feduccia did not examine any dinosaurs in his study.  The
manual and pedal anatomy of Archaeopteryx and dromaeosaurids are very
similar (except for the sickle-claw of the latter, of course).  The posture
of Archie is still a matter of debate, due to the ambiguities in Martin's
reconstruction.  Finally, we don't know that dromaeosaurids (or almost any
other theropod) lacked flight feathers, as none have been found in a
lithographic limestone.  I doubt it myself, but the data isn't there to
argue the point from positive evidence.

>
>You may not agree that the evidence points to arboreal Archie. Fair enough. 
>The evidence cited to support arboreal Archie is surely not unequivocal.
>But if Archie spent so much time running around on the ground, why don't 
>the points of his toeclaws look like a roadrunners(i.e. worn). IMHO, His 
>neat Jurassic manicure job is consistent with the arboreal theory but 
>contradictory to the cursorial theory. 

Actually, it would be interesting to see if Bahamian birds which run on the
beach have significant toe-wear.  Archie's Solnhofen environment wasn't much
like the Southwest, so the effect of substrate on toe-wear should be
checked.  Nevertheless, I will concede that the lack of wear is probably the
best evidence of arboreality in Archie.  However, the sharpness of the
toeclaws of maniraptoran theropods cannot be tesed in the same manner, since
(as mentioned above) none have been found preserved in environments which
would retain the impressions of the horny-part of the claw.

>
>Paul Sereno has provided a good minimum date for an arboreal lifestyle
>in birds. In his paper (Science, around Feb 92?) he suggested that Sinornis
>(Chinese bird) was occupying an arboreal habitat no more than 15 million 
>years after Archie. I don't recall him advocating an arboreal Archie, but
>he presented a very strong case for Sinornis to be arboreal at 135 million 
>years ago. 

Indeed, I (and everyone else I know of, for that matter) agree that Sinornis
was arboreal.

>
>---
>>By the way, I'm not wholly converted one way or the other to
>>cursoriality/arboreality.  Nevertheless, I've had to seek to undo disservice
>>done to the cursorial arguments by rigidly-arboreal theorists.  Hope these
>>comments are useful, and I appologize for their length.
>
>I consider myself more of a "cursorial basher" than "rigidly-arboreal 
>theorist", but I don't think my intellectually honest critique of the
>cursorial theory results in a "disservice" to anything. And I for one
>thank you for your comments and find them useful. Like many others, 
>I'm intrigued by the question of bird origins and enjoy a good debate 
>on the subject.

Fair enough, and I appologize myself for any disserviice.  I, too, enjoy a
good debate - that is the nature of science, after all.  Have any personal
opinions of the origin of tyrannosaurs... (semi-secret :-) ) 

Thomas R. HOLTZ
Vertebrate Paleontologist, Dept. of Geology
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Phone:301-405-4084