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



> > A more recent paper dealt with this.  TMM 41436-1
> is
> > probably _T. rex_.
> 
> 
>   He said or a close relative. We shouldn't ignore
> the
> earlier study, which noted that TMM 41436-1 does not
> closely resemble any T. rex maxilla, in addition to
> being far smaller. 69 Ma seems too old to be T. rex.
> That was probably the heyday of Tarbosaurus.

Time is not a control on taxonomy. Neither is
geography. If the alamosaurus-associated tyrannosaur
material is not assignable to any species with
confidence then it is at best, Tyrannosaurus sp., or
possibly Tyrannosauridae sp.

If you have monospecific genera, the temptation is to
drop all similar material into the single species,
then all sorts of incorrect assumptions get made. As I
stated before, this is what has happened all along
with the Tyrannosaurus and Torosaurus material form
the alamosaurus faunas. They are distinct from the
Lancian taxa, yet perhaps not distinct enough to
warrant individual species status. 

The trick is to resist the urge to pigeonhole all
specimens into taxa until you can be certain what that
taxon is. Brochu's assertion about the material is
correct.


> > >It must have been a smaller ancestor of T. rex.
> > 
> > Why "must"?
> 
>   It does appear closely related, but different and
> smaller, and older. The appearance of an apparent T.
> rex ancestor in a titanosaur dominated environment
> just prior to the Lancian and T. rex virtually
> clinches Starkov's case.It now does appear that T.
> rex
> evolved in response to titanosaurs.The Javelina was
> roughly coeval with the top of unit 4, where
> Albertosaurus was still the top predator in an
> environment lacking titanosaurs.It was also coeval
> with the Nemegt, where Tarbosaurus, fairly close to
> the ancestry of Tyrannosaurus, may have preyed on
> titanosaurs.
> 
>


Really, is there a need to have tarbosaurus come all
the way over from asia when we have perfectly good
tyrannosaur ancestors in the US already? Currie et al,
2003, place daspletosaurus, alioramus, and tarbosaurus
as the sister group to tyrannosaurus and nanotyrannus
(a juve, lets face it). daspletosaurus is present in
the Kirtland, underlying the Naashoibito, and is a
pretty big animal, if you think size is really a
measure of anything.


  
> 
>  I was only referring to Javelina titanosaurs,
> which,
> according to Lehman, made up about 70% of Javelina
> dinosaur specimens-even before more recent
> discoveries- whereas they were about 20% of
> Naashoibito dinosaurs, suggesting a decline by the
> time of the Lancian and T. rex, which could more
> effectively cull them.

nah, this isn't true. We shouldn't cling to the idea
that the Naashoibito is the same age as the Lance (see
how awkward this is? extending the term lancian to
include pre-lance fm strata is a dumb idea). There is
no evidence that the naashoibito is k-t boundary. If
anything, there is very good evidence that it is at
least very close if not contemporanaeus with thre
Javelina.

Oh, and Alamosaurus is by far and away the most common
animal in the Naashoibito. Lehman got his stratigraphy
confused (see various works by Sullivan et al);
understandable in many respects... but if you spend
long enough jumping across the basal conglomerate that
separates the underlying Kirtland and Naashoibito,
then you can figure out where in the section you are.



> 
>  
> > >They hadn't yet evolved the size necessary to
> take
> > on the titanosaurs in an
> > >environment dominated by them.
> > 
> > Even the largest of titanosaurs were small when
> they
> > were young. 
> 
>   But they probably derived protection from parents
> or
> other adult herd members.

this isn't demonstrable, and anyway there is no
evidence linking tiny little sauropod hatchlings as
staying with the adult herd, if indeed there were
herds.


> 
> 
> > BTW, it's 
> > my personal opinion that theropod predators
> > (including tyrannosaurs) 
> > typically targeted the smaller or weaker members
> of
> > a sauropod herd anyway, 
> > and avoided the larger and stronger individuals. 
> 
>  Maybe. But, as Starkov noted, there is a
> correlation
> between the rise of the largest sauropods and
> largest 
> theropods, suggesting the latter became bigger to
> overcome more massive prey.

this makes the assumption that adult tyrannosaurs
attacked adult titanosaurs which is rather unlikely. 


> 
> 
> 
> 
> > This would be more in 
> > keeping with the behavior of modern predators.
> 
>  I don't think they are quite as large in relation
> to
> prey as the biggest theropods.
> 
>  Tim
>  
>  
> 
> 
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