Notes on Rebbachisaurs and Tehuelchesaurus (longish)

[NJPharris@aol.com]

I recently obtained a copy of the following volume:

Tomida, Yukimitsu, Thomas H. Rich, and Patricia Vickers-Rich, eds.  
_Proceedings of the Second Gondwanan Dinosaur Symposium_.  Tokyo: National 
Science Museum, October, 1999.

The announcement about this volume went out in the latter part of last year.  
I have been reading through the papers and picked up a few tidbits that had 
not been discussed previously on the list.


Bonaparte, Jose F.  "An Armoured Sauropod from the Aptian of Northern 
Patagonia, Argentina".  in Tomida, Rich, and Vickers-Rich, pp. 1-12.

_Agustinia ligabuei_ is an armored sauropod from the Lohan Cura Formation 
(Aptian) of northern Patagonia.  It is based on a left hind limb, fragmentary 
dorsal, sacral, and caudal vertebrae, and some very peculiar osteoderms.  The 
osteoderms lay or stood over the midline of the back.  

The smallest structures are unpaired and leaf-shaped.  The largest are 
divided into two halves, each bearing a long, laterally-pointing spike.  
Other osteoderms are intermediate between the first two types, being 
rectangular in shape, with short laterodorsal projections.  There are eight 
reasonably well preserved osteoderms.  The author hypothesizes that they were 
"capable of being moved by the animal" (1).

The osteoderms apparently sat atop the greatly transversely expanded heads of 
the posterior dorsal and sacral vertebral spines.

One final note.  DGL Corrections # 115 reports that "[t]he dinosaur is 
undoubtedly related to the titanosaurians in some way", and I have seen this 
repeated elsewhere.  However, the author concludes:

"...within a limited range of comparisons, it is possible to admit that, 
based on the morphology of the neural spine, with four laminae at right 
angles, _Agustinia_ is more similar to members of the Rebbachisauridae 
(_Rebbachisaurus garasbae_ and _"Rebbachisaurus" tessonei_) than to those of 
the Titanosauridae...Possibly the presence of such heterogeneous types of 
osteoderms and the notably expanded top of the neural spines may be enough 
characters to propose a new family of Sauropoda, the Agustinidae [sic] nov."

As far as I can tell, there are no discernible features that would place this 
animal farther from _Rebbachisaurus_ than _Nigersaurus_ is, so I would 
instead advocate a provisional referral of _A. ligabuei_ to the 
Rebbachisauridae (everybody's favorite grab-bag of weird-ass Cretaceous 
diplodocimorphs :-)).


Calvo, Jorge O.  "Dinosaurs and Other Vertebrates of the Lake Ezequiel Ramos 
Mexia Area, Neuque'n - Patagonia, Argentina".  in Tomida, Rich, and 
Vickers-Rich, pp. 13-45.

Among MANY other things, Calvo defends the assignment of _R. tessonei_ to the 
genus _Rebbachisaurus_ and the referral of _Rayososaurus agrioensis_ to 
_Rebbachisaurus sp._


Rich, Thomas H., Patricia Vickers-Rich, Olga Gimenez, Rube'n Cu'neo, Pablo 
Puerta, and Raul Vacca.  "A New Sauropod Dinosaur from Chubut Province, 
Argentina".  in Tomida, Rich, and Vickers-Rich, pp. 61-84.

_Tehuelchesaurus benitezii_ [will that have to be changed to _benitezi_, 
George?] is based on a dorsal series and a smattering of ribs and limb 
elements from a single individual from the upper part of the Can~ado'n 
Asfalto Formation (Middle to Late Jurassic) of Chubut Province, Argentina.  
Based on the presence of opisthocoelous dorsal vertebrae with deep 
pseudopleurocoels, a relationship to the Chinese _Omeisaurus tianfuensis_ is 
advocated.

However, the authors refer to both _O. tianfuensis_ and _T. benitezii_ as 
"cetiosaurs" and make no mention at all of any other 
euhelopodids/mamenchisaurids, indicating that they are a little behind the 
times when it comes to sauropod classification.  Not to make light of the 
authors' work, but this seems to be a case of "We were working on 
_Tehuelchesaurus_ when we got a chance to examine _Omeisaurus_, and by golly, 
they looked kinda alike".

I have a feeling that the deep pseudopleurocoels, at least, may simply 
reflect the position of both _O. tianfuensis_ and _T. benitezii_ near the 
base of the neosauropod radiation, more than any special relationship between 
the two.  It will take a decent cladistic analysis of this critter (or at 
least a more inclusive examination of relevant taxa) to convince me that this 
is a South American euhelopod/mamenchisaur.

The girdle and limb elements of _T. benitezii_, BTW, are described as 
"somewhat similar to those referred to _Patagosaurus fariasi_" (62).

Whew.  That's it for now.  I'm tired.  Thanks for reading!

--Nick Pharris