Re: Theropod herbivory - parallel evolution or one clade?

[Jeff Hecht <jeff@jeffhecht.com>]

It's easier to climb up a tree than to get back down (ever have to rescue a cat 
from a tree?), and if you eat seeds or fruit, a tree offers pretty good eating. 
All you need is a way back down. Maybe it was easier for feathered theropods 
with arms long enough for climbing up the tree to just spread them out and 
glide back down. That may have been a stable ecological niche which didn't 
require major changes to the theropod body plan. 

At 2:53 PM -0600 11/17/06, Tim Williams wrote:
>Scott Hartman wrote:
>
>>Jeholornis was certainly a seed eater, and I wouldn't be shocked if 
>>Jinfengopteryx was (although I would be suprised if "Jinfengopteryx" is 
>>actually different enough to be separated from Sinovenator).  But niether is 
>>a climber, and Jeholornis was not landing in trees.
>
>I suspect they were all ungainly climbers, but climbed nonetheless.  You have 
>to start somewhere, after all.
>
>These feathered maniraptorans (including _Archaeopteryx_ and other basal 
>birds; microraptorans; maybe _Protarchaeopteryx_; maybe basal troodontids) 
>strike me as animals that were heading up into the vegetation, but didn't want 
>to relinquish their ancestral theropod 'bauplan'.  So they could put up with 
>being poor climbers and/or poor fliers, as long as they were comfortable 
>running on the ground.  Hence the retention of long legs, long tail, and 
>hand-claws.
>
>I don't see these ancestral theropod features as "baggage".  Instead, these 
>feathered maniraptorans wanted to hang onto their theropod roots rather than 
>commit themselves to the 'new-fangled' advanced avian (ornithoracean) bauplan, 
>with its forward-shifted center of mass and the complete re-modeling of the 
>pelvic limb that it required.  It's all a trade-off.
>
>It's all a Just-So Story, I know.  But avian evolution has traditionally been 
>viewed as a headlong rush to abandon all 'reptilian' characters in favor of 
>birdy characters.  To me, this doesn't do justice to the success of the 
>ancestral theropod bodyplan.  The presence of long-bony-tailed birds in the 
>Early Cretaceous, and even close to the end of the Cretaceous (_Rahonavis_), 
>tells me they were doing something right.
>

-- 
Jeff Hecht, science & technology writer
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