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RE: Rapetosaurus stuff



Various Rapeto-replies:
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Joao S. Lopes Filho
>
> But a faunal interchange between North and South America is necessary to
> explain the marsupials, ungulates, hadrosaurs, avisaurs. Alamosaurs is
> closer to South titanosaurs or to Asian titanosaurs?

According to their analysis, Alamosaurus is a basal member of a clade also
containing the Indian Titanosaurus colberti, South American Neuquensaurus
and Saltasaurus, and Asian Opisthocoelicaudia.  However, I would REALLY like
to see this analysis rerun by combining the Opisthocoelicaudia and
Nemegtosaurus data in the matrix, and seeing how it changes the results.

> If titanosaurs lived in Asia, where did they come from? How a Gondwanan
> group could reach Asia? Via Africa?Via some South Asian block coming from
> Australasia?

Previous studies have suggested that the Thai dinosaur Phuwiangosaurus is a
titanosaur, possibly close to the nemegtosaurs.

Furthermore, if titanosaurs are (as they seem to be) the sister group to
brachiosaurs, then the titanosaur lineage arose prior to the divergence of
northern and southern faunas.  Thus, titanosaurs could have had a global
distribution PRIOR to the Late Cretaceous, so migrations need not be
invoked.

(However, in finer detail, the biogeography can be studied by checking the
position of the various titanosaurs in their phylogeny).

> If the Angaran side of Asiamerican fauna had a kind of
> Gondwanan element, this could be the same way Gondwanan dromeosaurs reach
> Asia, since it being found a lot of interesting dromeosaurs in Argentina,
> many of them close to the birds .

By that comment I am assuming you are referring to Unenlagia, since the
other possible dromaeosaur of Argentina named so far, Megaraptor, is not
particularly bird-like.  More importantly, the dromaeosaurid lineage (if not
full-fledged classic dromaeosaurids) would go back at least to the Late
Jurassic.

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> christopher robert noto
>
>
> Has anyone considered the possibility that climate had anything to do with
> Alamosaurus remaining in southern NA?  I refer to an oldie but goodie:
>
> Lehman, T.M. 1987. Late Maastrichtian Paleoenvironments and Dinosaur
> Biogeography in the Western Interior of North America. Palaeogeography,
> Palaeoclimatology, Palaeoecology, 60: 189-217.
>
> In looking at various basins, the local geology, tectonic history, and
> their faunal constituents, Lehman suggests that the changes that occur in
> fauna from North to South (from a ceratopsian/hadrosaur to more
> titanosaurid dominated fauna as one moves southward).  Too often I
> think that we forget that dinosaurs were affected by climatic
> conditions and these may have affected their distribution.

Lehman has updated his work, most recently in:

Lehman, T.M. 2001. Late Cretaceous Dinosaur Provinciality.  in Tanke, D.H. &
K. Carpenter (eds.) Mesozoic Vertebrate Life.  pp. 310-328.

Lehman looks at Judithian (updating his 1997 paper in DinoFest), adds the
Edmontonian, and the Lancian (updating the 1987 paper).

For the Judthian, he finds a southern Kritosaurus-Parasaurolophus fauna (in
both upland and lowlan), a northern lowland Corythosaurus-Centrosaurus
fauna, and a northern upland Maiasaura-Einiosaurus fauna.  The Edmontonian
(admittedly more poorly studied) includes survivial of a
Kritosaurus-Parasaurolophus fauan in the south, an upland
Pachyrhinosaurus-Edmontosaurus fauna in the Montana-Alberta border region,
and an Anchiceratops-Saurolophus fauna further north in Alberta.  His
updated Lancian biogeography consists of a southern-to-central
Alamosaurus-Quetzalcoatlus fauna (known most from uplands), a central and
northern, mostly-lowland Triceratops-Edmontosaurus fauna, and a northern
uplands Leptoceratops-Triceratops fauna.  His new maps incorporate the
position of the Sevier and later Laramide orogenies in the western Interior
at each interval.

Lehman discusses both Asian and South American origins for Alamosaurus, but
further suggests the possibility that Alamosaurus is the survivor of North
American titanosaurs (as new work shows that titanosaurs were present in the
mid-Cretaceous of the U.S.).

One curious thing about North American Campano-Maastrichtian titanosaurs:
their teeth are not showing up in well-studied units like the Two Medicine,
Judith River Group, Horseshoe Canyon, and Hell Creek.  This does seem to
show that they weren't there.  On the other hand, if the Dinosaur Park
Formation therizinosaur frontal described by Currie in the 1980s IS a
therizinosaur, then those guys were hanging out in the Judith River Group
without leaving a tooth record (as far as has been reported).

Fun stuff.  And, although I forgot to mention this yesterday, congrats to
Drs. Curry Rogers, Forster, and the rest of the Madagascan expeditions for
yet another very cool discovery!

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796