Re: Triassic Sauropods

["Tim Williams" <twilliams_alpha@hotmail.com>]

Matt Bonnan wrote:

> However, the
> titanosaurid-like femoral morphology would make me lean towards a
> titanosaurid interpretation, or at least something in the 
> brachiosaurid-type lineage.
>
> As far as this material being an example of an early titanosaur from the
> Late Triassic or Early Jurassic, I would have my doubts.

Just a clarification: the term I used was "titanosauriform".  
Titanosauriformes = Brachiosauridae + Titanosauria.  If the sauropod 
material from the Isalo Group of Madagascar belings to some type of 
brachiosaurid (or at least shows "brachiosaurid" features") then it is 
probably basal titanosauriform.

> As Mickey Mortimer
> pointed out, the locality of the _Isanosaurus_ is not from the Isalo
> Formation in Madagascar but in Thailand instead.  This means the date for
> the Isalo Formation is probably not Late Triassic.

Actually, I was not referring at all to _Isanosaurus_ from Thailand.  I was 
referring to the Isalo Group of Madagascar.  (No, I'm not confusing the 
two.)

A Late Triassic age for the Isalo Group is given in :

Flynn, J.J. et al. (1999).  A Triassic fauna from Madagascar, including 
early dinosaurs.  Science 286 (5440): 763-765.

Abstract: "The discovery of a Middle to Late Triassic (apprx 225 to 230 
million years old) terrestrial vertebrate fauna from Madagascar is reported. 
This fauna documents a temporal interval not well represented by continental 
vertebrate assemblages elsewhere in the world. It contains two new 
prosauropod dinosaurs, representing some of the earliest dinosaur 
occurrences known globally. This assemblage provides information about the 
poorly understood transition to the dinosaur-dominated faunas."

_Lapparentosaurus_ and "_Bothriospondylus_" are not from the same site that 
yielded the "new prosauropods" (Isalo II, given as Middle Triassic), but 
from a slightly younger site, which may correspond to latest Triassic.

> I would like to see more complete material before drawing an "early
> titanosaur" conclusion for _Bothriospondylus_ and _Lapparentosaurus_.

Early *titanosaur* is probably out of the question, to be sure.  But early 
*titanosauriform* is more in line with what Argentine researchers have 
suggested for _Lapparentosaurus_.


Tim



------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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