Ameghiniana Round Up, Pt. II

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

The titanic papers...

Salgado, L., R.A. Coria & J.O. Calvo.  1997.  Evolution of titanosaurid
sauropods. I: phylogenetic analysis based on the postcranial evidence.
Ameghiniana 34(1):3-32.

A must for all sauropod workers (or dinosaur workers in general).  One of
several recent (and forthcoming) papers on sauropod phylogenetics.  At least
two nomenclatural conflicts show up in this paper!

The results:
Sauropodomorpha
-Prosauropoda
-Sauropoda
--_Vulcanodon_
--Eusauropoda nov. taxon (note 1)
---_Barapasaurus_
---Neosauropoda
----Diplodocidae (Diplodocoidea of most recent usage)
----Camarasauromorpha nov. taxon (note 2)
-----Camarasauridae
-----Titanosauriformes nov. taxon
------_Brachiosaurus brancai_
------unnamed taxon
-------_Chubutisaurus_
-------Titanosauria (=all descendants of most recent common ancestor of
Andesaurus & Titanosauridae)
--------_Andesaurus_
--------Titanosauridae
---------_Epachtosaurus sciuttoi_
---------_Malawisaurus dixeyi_
---------unnamed clade
----------unnamed advanced titanosaurid clade 1
-----------_Argentinosaurus huinculensis_
-----------unnamed clade
------------_Opisthocelicaudia skarzynskii_
------------"Titanosaurinae indet." (DGM "Serie B" of Powell's dissertation)
----------unnamed advanced titanosaurid clade 2
-----------_Aeolosaurus_
-----------unnamed clade
------------_Alamosaurus sanjuanensis_
------------Saltasaurinae
-------------_Neuquensaurus australis_
-------------_Saltasaurus loricatus_

(Conspicuous by their absence: species of _Antarctosaurus_, species of
_Titanosaurus_, _Argyrosaurus_, and the European titanosaur material).

Note 1: Paul Upchurch (1995. Phil. Trans. Royal Soc. B 349: 365-390) has
already used this name for a more exclusive taxon, namely Euhelopodidae +
Neosauropoda.  Barapasaurus was excluded from this taxon in Upchurch's
usage.  Unfortunately, the authors do not cite Upchurch's work.

Note 2: This taxon, "...the most recent common ancestor of Camarasauridae
and Titanosauriformes and all of its descendants", is seemingly the same
definition as the forthcoming Macronaria Wilson et Sereno 1997(?), mentioned
in Sereno's 1997 paper in Annual Reviews of Earth & Planetary Sciences.

38 characters used.

Some of the main conclusions:

"Andesauridae" is polyphyletic, as the previous "andesaurids" are either
basal titanosaurians (_Andesaurus_), basal titanosaurids (_Epachthosaurus_),
or derived titanosaurids (_Argentinosaurus_).

_Opisthocoelicaudia_ is a derived titanosaurid, with implications in the
next paper.

The presence of osteoderms can only be confidentally recorded in
_Saltasaurus_.  They could be more widespread (in all saltasaurines, all
advanced titanosaurids, etc.), but no positive evidence to support that at
present.

Of Powell's four subfamilies, only Saltasaurinae was supported (though, to
be fair, neither _Argyrosaurus_ nor species of _Antarctosaurus_ were
included, so their validity cannot be examined in this study).
Titanosaurinae, however, is based on basal titanosauriform and basal
titanosaurid characters, and is paraphyletic.

Salgado, L. & J.O. Calvo.  1997.  Evolution of titanosaurid sauropods. II:
the cranial evidence.  Ameghiniana 34(1):33-48.

More evidence that the skulls of titanosaurids were not diplodocid-like (as
restored by Huene) nor extremely-flat (as suggested by Jacobs), but were
instead _Camarasaurus_- (or especially _Brachiosaurus_-) like in form.  The
occulsion of titanosaurid teeth is different from that found in other
sauropod groups, especially diplodocoids.

The authors provide new restorations of the skulls of _Antarctosaurus
wichmannianus_, _Nemegtosaurus_, and _Quaesitosaurus_.  These latter two are
titanosaurians, possibly titanosaurids.  Perhaps (as previously suggested)
_Nemegtosaurus_ is the head of _Opisthocoelicaudia_?

The authors find that "Brachiosauridae" (sensu McIntosh) is polyphyletic.
Some "brachiosaurids" (_"Bothriospondylus" madagascarensis_ &
_Bothriospondylus suffosus_) may be basal sauropods or basal neosauropods,
others are basal titanosauriforms, and some are true titanosaurians.
_Brachiosaurus altithorax_, _Brachiosaurus brancai_, and some of the Wealden
forms are basal titanosauriforms.  The authors note that no unequivocal
synapomorphies unite the American and African "_Brachiosaurus_" species
outside of other basal titanosauriforms: perhaps we should get used to using
_Giraffotitan_ as a valid generic name?

_Janenschia robusta_ seems to include the earliest titanosaurid material,
but the hypodigm of this species is composed of all sauropods that couldn't
be placed in the other Tendaguru sauropod taxa.  More than one taxon may be
present in the material, as McIntosh has also observed.

_Pleurocoelus nanus_ (aka _Astrodon johnstoni_) is found to be the probable
sister taxon to Titanosauria, and some of the Texan material referred to
"_Pleurocoelus_" is titanosaurian.

_Austrosaurus_ sp. (from the Winton Formation of Australia) is a
titanosauriform.

Among the Early Cretaceous English forms, _"Titanosaurus" valdensis_ is the
oldest confirmed titanosaurid, and _Pelorosaurus_ and _Macrurosaurus_ are
titanosauriforms close to Titanosauria.  The authors suggest a European
origin for the Titanosauridae.

Other definite titanosaurids not covered in the first paper: _Aegyptosaurus
baharijensis_ and _Argyrosaurus superbus_.  _Antarctosaurus wichmannianus_
is probably a true titanosaurid more derived than _Malawisaurus_ or
_Pleurocoelus_, and is clearly a titanosaurian at least.

Those are the highlights.  It will be interesting to compare their results
with Wilson & Sereno's paper when it comes out.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661