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Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveries)




--- Tim Williams <twilliams_alpha@hotmail.com> wrote:

> Denver Fowler wrote:


> >this makes the assumption that adult tyrannosaurs
> attacked adult 
> >titanosaurs which is rather unlikely.
> 
> Agreed.  Unless the adult titanosaur was wounded or
> sick.


P. Currie mentioned healed bite marks on sauropod bone
from the Morrison, IIRC, suggesting that even early
theropods attacked sauropods capable of defending
themselves.



 
> I haven't read any of Starkov's stuff, but I'm
> inferring from your statement 
> that he is claiming that the largest sauropods
> co-existed with the largest 
> theropods.  Although it's an intuitively attractive
> idea, I don't believe we 
> have the data to back it up. 

 Giganotosaurus and Argentinosaurus,
Carcharodontosaurus and Paralititan,
Torvosaurus/Epanterias and Brachiosaurus etc. Starkov
mentioned other examples.


> For example,
> _Tyrannosaurus_ was a very large 
> theropod, but _Alamosaurus_ was not that impressive
> by sauropod standards.  

 As others have pointed out, it WAS massive, and
brachiosaur-like IIRC.

> Similarly, the Nemegt sauropods were not
> spectacularly large, and these were 
> the guys who rubbed shoulders with _Tarbosaurus_. 


 Yes, but Tarbosaurus was smaller than T. rex, which
faced bigger sauropods in North America. It is
noteworthy that the most Tyrannosaurus-like taxa c mid
Maastrichtian lived alongside titanosaurs. Of course
the Nemegt had other potential prey besides O.
skarzynskii- Saurolophus for example. But Saurolophus
also existed in upper Edmonton environments lacking
titanosaurs. Albertosaurus remained the top predator
there to c mid Maastrichtian. Based on that, and the
Tyrannosaurus-like TMM 41436-1 in a titanosaur
dominated mid Maastrichtian environment, it appears
that Starkov is right about the origin of T. rex. Like
previous theropod giants, it apparently arose in
response to large sauropods.
 Btw, IIRC a juvenile titanosaur was found not far
below the K-T in the Black Peaks formation overlying
the Javelina, so the "Alamosaurus" fauna may have
persisted to the end. But titanosaurs may not have
been as numerous in the late Maastrichtian as they
were c 69 Ma. T. rex is apparently present in the
McRae and in the North Horn, but "Alamosaurus" is
known from a single limb bone in the former unit
(where Torosaurus seems more common). That's quite a
contrast with the Javelina, and might reflect the
increased culling power of T. rex compared to the
smaller Javelina tyrannosaur.


> All post-Triassic 
> terrestrial Mesozoic habitats were probably home to
> theropods and 
> dinosaurian herbivores of different shapes and
> sizes; but I don't think we 
> can pair up the carnivores and herbivores based on
> size alone.

 Maybe not on size alone but it does seem important. 
 


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