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



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

> 
> 
> --- 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.

But how big was the sauropod? Saurophaganax and
Torvosaurus were big enough to have a good go at a
medium sized sauropod maybe. 

Anyway, if we're talking about prey etc, Tyrannosaurs
probably preyed on anything they could, including
titanosaurs if they could kill them, and there would
have been more juve/subadult sauropods around than
gigantic adults. At the same time, Alamosaurus faunas
contain all the other usual suspects: hadrosaurs,
ceratopsians etc. Why associate T.rex evolution with
sauropods?

Tyrannosaurs are always present with hadrosaurs, in
both Asia and North America, and usually with
ceratopsians. They are not always present with
titanosaurs. Here's a good question. Where do the
biggest ceratopsians and hadrosaurs occur? with T.rex.


> 
> 
> 
>  
> > 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.

This is true. But it is a misleading statement.
Sauropods are ubiquitous across the globe all through
mesozoic time except (arguably) for North America
between the cenomanian and early maastrichtian (yes
yes, possibly a little earlier even depending on the
AZ and De-na-Zin material). Sauropods invariably
include the largest-bodied constituents of their
faunas. Hence, wherever you get large theropods, there
will be large sauropods, except in N. Am as stated
above.

regarding the largest sauropods... well your
suggestion is that theropods get big specifically to
combat big sauropods, but it is equally probable that
theropods got bigger first, so sauropods had to get
bigger still to maintain any form of immunity as an
adult. All more-or-less unprovable, but it
demonstrates that bodysize evolution pressures could
occur at either end, or in the middle, of a range of
possibilities.

> 
> 
> > 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. 

But the taxon 'most like T.rex': T.rex itself, didn't
live 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. 

JOP, Lehman & Coulson, 2002

>From my understanding, the contact of the Javelina and
Black peaks is every bit as complicated as the
Naashoibito and Kimbeto (and thus should similarly not
be afforded formation status). Admittedly, if the
stratigraphy of this specimen is indeed 150m into the
black peaks, then maybe titanosaurs did survive a bit
later. 

That said, subsequent confusion surrounding the
stratigraphy and palaeontology of the Kirtland,
Naashoibito, and Kimbeto (e.g. Lawson 1976, Lehman,
1981, and subsequent publications) should mean we
proceed with caution when talking about the remarkably
similar Agjua, Javelina, and Black Peaks, although we
do have an ash date for the Javelina, which is nice.




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.

You could fit all the even vaguely diagnostic material
collected from the McRae onto a single (admittedly
large) table. And anyway, you are suggesting here that
the McRae is of the same age as the Lance Fm, simply
because it contains some large Tyrannosaurus sp.
material. Which is not possible to conclude,
especially given the ash date of the javelina: much of
the point about my posts to date.

Anyway, don't confuse what you see in a museum (read
uBer-bias here) to what you see in the field. The
problem with sauropod vertebrae is that, apart from
caudals, they are made of very thin easily destroyed
bone. You see no shortage of 'Alamosaurus' vert
material in the field, very often from dorsals and
cervicals (which are very poorly represented in
collections). Unfortunately these aren't usually worth
collecting as even in those situations when you can
extract the bones without them falling into powder,
they are little more than a lump of centrum.

Removal of such fragile material is facilitated
somewhat by serious use of <shock!> Cyanoacrylate:
simply, the only freely available, affordable (for an
entire sauropod vert) surface consolidant up to the
task.

Anyway, going back to the point: It is alot easier to
collect non-sauropod material, than it is to collect
sauropod material; Which would you rather
extract/carry?: half a dozen t.rex teeth, a solid
torosaurus parietal, or a pretty crappy metre long
sauropod vert in a big plaster jacket that is falling
apart and won't be diagnostic of anything anyway? If
sauropods seem under-represented <in collections>,
it's probably a collecting bias. 

Denver.

> 
> 
> > 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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