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Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveries)
--- Denver Fowler <email@example.com> wrote:
> Do you really mean T.rex here, or just
> be careful as the two should not be considered as
> meaning exactly the same thing. (this is a long and
> winding road, but hopefully it should all make sense
> in the end)
Brochu said TMM 41436-1 was T. rex or a close
relative. The latter is probably true given the age of
the Javelina and the relatively small size of TMM
41436-1. (Carpenter also mentioned a short face
compared to T. rex.)It must have been a smaller
ancestor of T. rex. I once suggested the small size of
Javelina tyrannosaurs indicated an earlier age for
that unit. No wonder its tyrannosaurs were rather rare
and Alamosaurus so common. They hadn't yet evolved the
size necessary to take on the titanosaurs in an
environment dominated by them.
> Material assigned to the dustbin taxon 'Alamosaurus'
> may or may not represent a single genus or species.
> Thus, the occurrence of titanosaurs in the late
> cretaceous of southern North America does not
> necessarily imply the deposits are the same age.
True. Williamson denied that titanosaur material was
from the De na zin, but IIRC sauropod remains are
known from the Campanian Ft Crittendon and the Aguja.
> fact, 'Alamosaurus' is probably a very bad choice
> a biomarker since the holotype material bears no
> Let's say for argument's sake that all 'Alamosaurus'
> material is contemporaneous. The best 'Alamosaurus'
> material derives from the TX Javelina Fm, dated as
> 69Ma, give or take, which thus predates the classic
> Lancian faunas of the north.
I suspected the Javelina was older than the
Lance/Hell Creek, for reasons above and the lack of a
K-T impact signature.
> Let's look at a near identical case: Torosaurus
> The collapsing of T.utahensis and T.latus into just
> T.latus (thereby creating another monospecific
> merely implies a single lineage of Torosaurus, not
> that all Torosaurus material is contemporaneous. The
> slight variation seen between T.latus and
> might not be enough to warrant a different species,
> but there are differences, probably representing a
> small number of accumulated changes between (and
> during) North Horn and Lance Fm time. For southern
> faunas, all other published dinosaur material
> comparable to Lance Fm taxa is indeterminate (e.g.
> farke ?2002?, or Sullivan/Lucas ?2004?), although
> specimens may change this.
> T.rex from the Lance/Hell Creek represents the last
> occurrence of a tyrannosaurid in the fossil record.
> Tyrannosaurus from the south represents the second
The Javelina may be older than the Lance but what
about the McRae? A T. rex sized tyrannosaur was found
>This is exactly the same for the ceratopsians,
> most notably Torosaurus, but also probably
> Triceratops, and might be the same for hadrosaurs
> ankylosaurs pending study of new material. The
> in the south is the presence of titanosaurs.
> What 'age' is the Alamosaurus fauna?
> If the Javelina is around 69ma, and the
> alamosaurus-bearing formations are indeed the same
> age, then Alamosaurus faunas represent not a
> but a pre-Lancian age. Inappropriate assignment of a
> 'Lancian' age to the Alamosaurus fauna might be seen
> to imply contemporaneity with the Lance Fm, which is
> incorrect. What we are actually now seeing is the
> extension of T.rex down to 69ma,
I doubt it. TMM 41436-1 is apparently not T. rex and
the McRae and Naashoibito are probably Lancian. IIRC
Williamson cited Essodon as further evidence for a
Lancian age for the Naashoibito.
> not the cementation
> of the Alamosaurus fauna up to the K-T boundary.
> is an important distinction to make, as it serves to
> illustrate that sauropods, lambeosaurines, and
> centrosaurines all seem to disappear from the north
> American record before the lancian.
Centrosaurines, yes. Lambeosaurines and nodosaurs
may have disappeared by late Lancian time. Maybe not
titanosaurs, although they do seem less common in the
apparent Lancian age SW units than in the Javelina.
> So what does this mean? Well <I would argue>, it
> suggests that we see alot finer stratigraphic
> resolution in the North American late-K dinosaur
> record than is currently recognised, and this has
> important implications for dinosaur diversity (turn
> down). The classic 'judithian' 'edmontonian' and
> 'lancian' mammal-based faunas are either separated
> gaps, or could arguably be split further by the use
> dinosaurian taxa (primarily ceratopsian and
> hadrosaurid), and the fact that very few
> dinosaur-bearing horizons are actually
> contemporaneous. Read the Kirtlandian paper by
> Sullivan & Lucas. It makes alot of sense.
> back to work...
> > should be noted that Tarbosaurus, probably closest
> > to
> > the ancestry of T. rex, is abundantly preserved in
> > the
> > Nemegt formation, which had a fair number of
> > titanosaurs. That suggests titanosaurs did
> > tyrannosaur evolution. Tyrannosaurus may have
> > evolved
> > larger size to overcome titanosaurs in far inland
> > environments, then spread to the lowlands.
> > Btw, ankylosaurids may have been present in the
> > Leptoceratops habitats but they were hardly among
> > the
> > dominant taxa there. AFAIK only two A.
> > specimens are known from the Scollard.
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