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Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveries)
--- Denver Fowler <email@example.com> wrote:
> 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
> drop all similar material into the single species,
> then all sorts of incorrect assumptions get made. As
> 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.
TMM 41436-1 is probably a different taxon, but the
McRae tyrannosaur specimen is big enough to be rex.
> The trick is to resist the urge to pigeonhole all
> specimens into taxa until you can be certain what
> taxon is. Brochu's assertion about the material is
> > > >It must have been a smaller ancestor of T. rex.
> > >
> > > Why "must"?
> > It does appear closely related, but different
> > smaller, and older. The appearance of an apparent
> > 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
> > 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
> > 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
> 2003, place daspletosaurus, alioramus, and
> as the sister group to tyrannosaurus and
> (a juve, lets face it). daspletosaurus is present in
> the Kirtland,
The de na zin is of Campanian age. The Nemegt and
Tarbosaurus are temporally closer to T. rex and
migration across the Bering was obviously possible at
the time e.g. Saurolophus. Moreover Tarbosaurus is
said to have features in common with T. rex which are
currently unknown in Daspletosaurus. Maybe TMM41436-1
is more closely related to T. rex, but it's just a
>underlying the Naashoibito, and is a
> pretty big animal
Not as big as Tarbosaurus.
> > 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
> how awkward this is? extending the term lancian to
> include pre-lance fm strata is a dumb idea). There
> 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
I knew that the K-T boundary isn't known in most/all
of these SW units. So Williamson is wrong about the
age of the Naashoibito? He based a Lancian age on T.
rex like teeth and Essonodon IIRC.
> Oh, and Alamosaurus is by far and away the most
> animal in the Naashoibito. Lehman got his
> confused (see various works by Sullivan et al);
> understandable in many respects... but if you spend
> long enough jumping across the basal conglomerate
> separates the underlying Kirtland and Naashoibito,
> then you can figure out where in the section you
> > > >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
> > 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
> > > 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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