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




--- Denver Fowler <df9465@yahoo.co.uk> wrote:


> 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.

 But adults may have protected them. In any event
there is evidence that tyrannosaurs were fairly
audacious. Healed bite wounds are known in Triceratops
and ankylosaurs as well as in hadrosaurs. 



> At the same time, Alamosaurus
> faunas
> contain all the other usual suspects: hadrosaurs,
> ceratopsians etc. Why associate T.rex evolution with
> sauropods?


 Because the closest relatives of T. rex c mid
Maastrichtian lived alongside titanosaurs, whereas
contemporary Edmonton faunas which lacked them had
Albetosaurus.

> 
> 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.


  The most massive hadrosaurs may have been giant
lambeosaurs from the Campanian El Gallo and elsewhere.
IIRC an Anatotitan has been found which is as large as
Shantungosaurus, but the latter apparently faced
Tarbosaurus.

  
> > > 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.

 Starkov cited a number of examples, at least one from
the Cenozoic, where herbivores got bigger first. 


> 
> > 
> > 
> > > 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.

 It could well have, given the McRae specimen. After
evolving in titanosaur environments, Tyrannosaurus
apparently spread to the lowlands, causing escalation,
and some extinction.

> 
> 
> 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.


 But the McRae has a tyrannosaur big enough to be of
Lancian age-a lower jaw which looks like it's from T.
rex- whereas the Javelina apparently has just a
smaller relative, consistent with an older age.












> 
> 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
> 
=== message truncated ===



                
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