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



--- Tim Donovan <uwrk2@yahoo.com> wrote:

> 
> 
> --- Denver Fowler <df9465@yahoo.co.uk> 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
> > 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. 
> 
>   TMM 41436-1 is probably a different taxon, but the
> McRae tyrannosaur specimen is big enough to be rex.
>  


Size is not an autapomorphy. There is very limited
material known from the Naashoibito of a large
near-rex size tyrannosaur. The McRae material is
undoubtedly large enough to be t.rex, and may well
belong to that taxon, but size alone is not enough to
assign the species rex (or indeed any species) to this
tyrannosaur material. 

Perhaps you are right: perhaps the McRae material is
T.rex, but we can not tell for sure from the specimen.
this runs circular to my original statement: the
presence of titanosaur material in a given formation
is no guarantee of contemporaneity. And again, if all
the javelina, naashoibito, north horn, and Mcrae
material are indeed contemporanaeous then they are of
pre-lance fm age. And again, if the associated
tyrannosaurids are indeed T. rex then this taxon's
range is thus extended down beneath the base of the
lance fm.

  
>  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
> maxilla.

It is indeterminate material. T.rex is probably a
product of peramorphosis anyway: compounding the
problem in identifying scraps of anything apart from
fully mature adults.

> > 
> > 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.
> 
>   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.

The K-T boundary, is not likely present in the
Naashoibito. Anyway, fossil material is concentrated
in the lower half of the Naashoibito, which is handy
cause the overlying boundary with the Kimbeto sst is
very hard to distinguish, hence they are both members
of the Ojo Alamo Fm.

Williamson's designation of T. rex to teeth from the
Naashoibito does not prove anything. First of all,
tyrannosaurid teeth are notoriously difficult to
assign, even to the genus level, with any great level
of confidence. Furthermore, even if this is T.rex, it
does not indicate a Lance-age assignment to the unit. 

Regarding Essonodon, there is very little material
upon which to base this assertion. I freely admit to
not being a mammal worker, but I am reliably informed
that the acclaimed Essonodon material may not be
exactly the same as the Lance.

And anyway, who cares if it is? The fact remains that
the only hard date we have for any of the southern
faunas is 69ma for the Javelina, and its titanosaurs.
If any taxa are associated with this date then all it
serves to do is drag down T.rex, Essonodon,
torosaurus, Triceratops, and god knows howe many other
taxa down out of an exclusive Lance position.

Likely, the Alamosaurus fauna represents a unit of
time unrepresented in the north (in a similar vein to
how the Kirtland Fm is also a unique time slice). This
is pre-lance fm, and there is no evidence to suggest
fossil material is present in any abundance up to the
K-T boundary, if indeed it exists. North American Late
K stratigraphy is not as simple as it has been painted
so far. Loris Russell acknowledged that gaps existed
in his classic judithian-edmontonian-lancian ages. He
was right. 

>   
> > 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.
> 
> > 
> > 
> > 
> > > 
> > > 
> > > 
> 
=== message truncated ===



                
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