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Titanosaurs



There are only two titanosaurs skulls known that are verifiably 
titanosaur, right? I'm not sure I want to include *Nemegtosaurus* and 
*Quaesitosaurus* in that main grouping, for their skulls look too much 
like diplodocids than they do the one skull belonging to 
*Antarctosaurus*. The skull of *Argentinosaurus*, on the other hand, is 
actually quite similar, and makes me suspect that titanosaurs were 
related closely to the diplodocids, or at least, since they show some 
macronarian details in the skull (the mandible, especially) came from 
about the split of diplodocid from macronarian, as in the following 
clade:

o = ancestrous cetiosaur
|
*Shunosaurus*
|
*Euhelopus* and kin
|               | |
Macronaria      | *Mamenchisaurus*
|               |               |
Camarasaurids   Titanosaurids   Diplodocids
&               &               &
Brachiosaurids  Saltasaurines   Dicraeosaurids

If this clade is acurate, or close to the truth, than titanosaurs are 
basal diplodocids stemming from advanced "euhelopodids", who actually 
share features with the later branches as do the "genasaurs" like 
*Heterodontosaurus* and *Lesothosaurus,* who each gave rise to a major 
branch of Ornithschia = Marginocephalia and Thyreophora, respectively.

And, if so, then the ancestor to the brachs and camaros would be 
*Omeisaurus*, to the diplodocids would be *Mamenchisaurus*, and to the 
titanosaurs a form based on *Euhelopus* with a specialized set of teeth 
later adapted by the diplodocids -- or the titanosaurs derived from 
*Mamenchisaurus* as well, but diverged early on, thus retaining their 
"basal macronarian" status yet having "diplodocid" features as the 
peg-shaped teeth, the scapula's shape being similar between 
*Neuquenosaurus* and *Diplodocus* and even *Apatosaurus,* plus the 
pelvis is more like diplodocids than camarasaurs or brachiosaurs.

How *Nemegtosaurus* and *Quaesitosaurus* fit in, I don't know, but as 
for *Opisthocoelicaudia*, a possible derived "euhelopodid" status is not 
out of the question, closer to camarasaurids than to titanosaurs. I, for 
one, do not believe *Nemegtosaurus* and *Opisthocoelicaudia* are 
synonymous.

Yet titanosaur remains are so incomplete as to assert that no definable 
profile on even _one_ is possible. How can this be, when we have 
complete "euhelopodid," camarasaur, diplodocid, and mostly complete 
brachiosaur skeletons? Was it the Southern Hemisphere? All the other 
families are largely confined to the Laurasian continents, even back 
then. But Australian *Rhoetosaurus* (?), South American multitudes, 
Indomadagascarian (India and Madagascar as a sub- continent) 
*Titanosaurus,* and a lack of African (which I don't believe, and you 
can bet I'm holding my breath) parts. British, European, and Asian 
remains are suspect anyway.

The general concensus is this, then: diplodocid-like with osteodermal 
armor, short tails, long- and possibly even-legged, and a deep or long 
skull on a medium to long neck help upright.

All titanosaurs need to be studied in one paper or a series, to be 
compared to each other in one study to formulate a basic interpretation 
of them all. That is, to define the Titanosauridae, Titanosauroidea, 
Titanosauria, and Titanosauriformes, plus the "Andesauridae," 
"Saltasaurinae," and "Nemegtosauridae."

Until then (or a response, which ever comes first),

Jaime A. Headden

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