Re: Taxonomic Status

["Jaime A. Headden" <qilongia@yahoo.com>]

Ivan Kwan (t_rexkwan@hotmail.com) wrote:

<Just what is Antarctosaurus? Is it a titanosaur, or is it (as i read  
somewhere else) a
diplodocimorph?>

  It's both. Or rather, the holotype of the type species, *A. wichmannianus* 
von Huene, 1927, from
the Allen Fm. near Roca (same region and strata as *Quilmesaurus*), appears to 
be a
diplodocimorph, and possibly allied with *Nigersaurus*. The skull is especially 
similar to several
diplodocimorphs, but is not as "rotated" so that the braincase faces ventrally 
at the rear. The
mandible is especially diagnostic. A second species, *A. septentrionalis* von 
Huene, 1932, was
removed as a titanosaurid called *Jainosaurus,* named for Sohan Jain, and was 
an Indian
titanosaur, and similar to both *Argyrosaurus* and *Titanosaurus.* A third 
species, *A. giganteus*
von Huene, 1929, is also a titanosaur, from the Neuquén Fm.. Obviously, *A. 
giganteus* is not
*Antarctosaurus.* Other titanosaur material referred to *Antarctosaurus* looks 
like nemegtosaur
material (see Curry-Rogers & Forster, 2001).

<By the way, did Titanosaur heads vary that much? I know that sauropod skulls 
are exceedingly
rare, but I have seen many restorations of them with squarish, camarasaur-like 
heads, while the
recent finds of Rapetosaurus and Nemegtosaurus seem to show otherwise. What is 
the consensus,
folks? Did some titanosaur families have square heads while others had slender 
skulls? Or did all
of them convergently evolve a nice diplodocid-like head?>

  Titanosaur heads did indeed vary, but the simple answer, I think, is not 
transformation from a
boxy skull to an elongated skull, as supported by analyses with *Malawisaurus*, 
as the
plesiomorphic condition is that of a brachiosaur-type skull, which persists 
into the
Titanosauroidea and Titanosauridae, with some titanosauroids (nemegtosaurs) 
having a more
diplodocoid-style skull, but the basal forms having a much more square skull 
from the lateral.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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