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early birds, etc.



>
>>>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.
>
>I think that most theropods could have gone right up a tree and probably
>get up as fast as almost anything given their comparative athleticism.
>But this is a non sequitor. Just because Mark Spitz can swim well doesn't 
>mean he shares a niche with the manatee. Basic survival skills like swimming 
>or climbing are things that most vertebrates can do to some level. The 
>question of what lifestyle theropods are adapted for leads most scientists 
>to a conclusion of theropods being highly adapted to a terrestrial 
>environment.

Adaptations for terrestriality and arboreality are not mutually exclusive.
The modern felids (from wild cats and ocelats upt to jaguars and leopards)
work very well both on the ground and up in trees.

>None of the arboreal characters Sereno cites for Sinornis
>have been described for any theropod.

Nor are they found in Archaeopteryx.

>
>As far as physical size goes, I was referring more to the body length, not 
>the mass:

For most aspects of biology, mass is the most important measure of size.
However, I agree that length is probably a better measure

>       - Sinornis      < 1'

Sinornis is quite a bit smaller - between finch and cardinal, approximately.

>       - Archie        < 3'
>       - Dromaeosaur     6'
>       - Troodon         6'
>       - Velociraptor   10'
>       - Deinonychus    10'

Hold on there.  Velociraptor is not, has never been, nor ever will be
(probably) 10' long.  It was a small animval, 6' for a large individual.  As
most of you know, the animal called "Velociraptor" in Jurassic Park is
actually Deinonychus (they actually use the trivial name "antirrhopus" in
the text).  Although Greg Paul did synonymize the two genera, most people
who work on theropods would agree that that's going a bit too far (although
we also agree that Velociraptor and Deinonychus are members of the subfamily
Velociraptorinae).

>
>I'll restate it by saying that it's easier to navigate through trees with
>a one foot broomstick out your butt than it is with a 3 foot broomstick.
>--- 

It depends how deep the forest is - in a less dense region, the "broomstick"
would be a useful counter-balance (antirrhopus).

>>
>>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.
>
>I would suspect that beach runners exhibit a similar wear since quartz 
>registers 7 on the Mohs scale no matter if it's in the desert or on a beach.

But there was next to nil quartz sand in the Solnhofen carbonate banks.  It
was mostly a limey mud.  Carbonates, especially as mud, would have very low
Mohs hardness.

>---
>>Indeed, I (and everyone else I know of, for that matter) agree that Sinornis
>>was arboreal.
>
>We have a consensus! Seems like everyone agrees that birds were arboreal
>by no later than 135 million years ago. I predict that this date will be
>pushed back even farther in future studies.
> 

This is probably true for Sinornis' lineage.  However, almost all other
Mesozoic birds (Icthyornis, Hesperornis, Patagopteryx, the
Enatornithoformes, etc.) are demonstrably nonarboreal.  Thus, Sinornis shows
that birds were capable of evolving arboreal forms, but is phylogenetically
distant from the common ancestor of modern perchers/tree dwellers.

>>---
>[deleted]
>>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 :-) ) 
>
>I do, but they will have to wait for SVP ;-)
>
>

See you there.

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