Re: New Dinosaur from Argentina (DINOSAUR digest 1320)

["Steve Brusatte" <dinoland@mailcity.com>]

On Sun, 12 Mar 2000 10:32:48   DRosent288 wrote:
>I think there was on sauropod that may have shared its environment with T. 
>Rex:
>Alamosaurus sanjuanensis.
>

Yeah, I think that is all that is really known to science now.  I *think* this 
new giant dinosaur from Texas most likely shared its environment with T. rex, 
but it may turn out just to be another species of Alamosaurus.  I don't think 
any technical literature on this new dino will be published for some time.

Back to the discussions on the evolution of large size in theropods.  When 
looking at the environment in Argentina 100 million years ago you do see a few 
large sauropods and a few large theropods.  So, the question that a few members 
on the group has been asking is "did the size of these sauropods push these 
theropods to evolve large sizes?"  When looking at the data from my non-PhD, 
still in high school perspective, this seems to be the most plausable answer.  

BUT: Yes, as somebody pointed out (I recall) T. rex evolved a huge size with 
the only one, single sauropod in its environment, and likely Alamosaurus was 
not its major quarry.  Tyrannosaurs are most often referred to as hunting 
hadrosaurs, for the most part.  So, rex evolved a huge size without a huge 
sauropod.  Does that mean that, indeed, the two huge sauropods (Argentinosaurus 
and possibly the new one from Argentina) had nothing to do with the evolution 
of this new Argentine theropod and Giganotosaurus?

And, number two, in all reality Giganotosaurus and this new theropod would most 
likely not be hunting the adults of the Argentinosaurus species!  Estimates 
have Argentinosaurus at over 100 feet, and I don't know if even a pack of these 
new theropods could take a full grown one of these down!  Instead, they were 
probably hunting the small, weak, and wounded of the Argentinosaur species, 
especially the children (Matt Wedel commented that possibly only 1 out of 500 
sauropod babies would survive until adulthood!).  There would also probably be 
a great deal of scavenging on dead Argentinosaur carcasses.  So, if these large 
theropods were not hunting adults of the sauropod species, why would they need 
to get so big?

This brings me to the question: were two species of large, meat eating 
dinosaurs competing, in an evolutionary sense, to "get the prey," and therefore 
evolved large sizes?  Was it an arms race?  Could Giganotosaurus and the new 
guy have been directly competing?  Well, it seems like Giganotosaurus and the 
new theropod were separated by a few million years, so this is probably not the 
case either.

Was there possibly another large, so far undiscovered theropod, that 
Giganotosaurus or this new guy would have been competing with in life?

Okay, this brings me to the end of my post, which is likely filled with a lot 
of fallacies and evolutionary impossibilities, and so on and so forth.  But, I 
am interested in hearing what some of you other dinosaur groupies have to say 
about this; especially you 'experts.'  

Steve
Dino Land Paleontology
http://www.geocities.com/stegob


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