Re: Triassic Sauropods (Cretaceous ones meanwhile)

["David Marjanovic" <david.marjanovic@gmx.at>]

> The known skulls of Late
> Cretaceous sauropods tend to be crushed and/or fragmentary.  The skull of
> _Nemegtosaurus_, like the skull of _Antarctosaurus_, has traditionally
been
> reconstructed with _Diplodocus_ in mind.  However, several researchers
> (Salgado, Calvo among them) have presented a strong case for re-building
the
> skull more along the lines of _Brachiosaurus_ than diplodocids.

> Is the skull of _Nemegtosaurus_ more diplodocid-like or
brachiosaurid-like?
> This appears to lie in the eye of the beholder.

Not entirely.

Paul Upchurch: The phylogenetic relationships of the Nemegtosauridae
(Saurischia, Sauropoda), JVP 19(1): 106 -- 125, March 1999

makes a very good case for (I hope this lines up on your screens)

Sauropoda
 |--Vulcanodon
 `--+--Barapasaurus
      `--Eusauropoda
           |--Euhelopodidae
           |    |--Shunosaurus
           |    `--Euhelopus + Mamenchisaurus + Omeisaurus
           `--+--Patagosaurus
                `--+--Cetiosaurus
                     `--+--Haplocanthosaurus
                          `--Neosauropoda
                                |--Diplodocoidea
                                |    |--Nemegtosauridae (N. +
Quaesitosaurus)
                                |    `--+--Rebbachisaurus
                                |         `--+--Dicraeosauridae
(Amargasaurus + D.)
                                |              `--Diplodocidae (Apatosaurus
+ (Barosaurus + D.))
                                `--Camarasauromorpha (what about
Macronaria?)
                                      |--Camarasaurus
                                      `--Titanosauriformes
                                            |--Brachiosauridae (B. +
Lapparentosaurus)
                                            `--Titanosauroidea
                                                  |--Phuwiangosaurus
                                                  `--+--Andesaurus
                                                       `--+--Malawisaurus

`--Titanosauridae (hm, what about Saltasauridae?)

|--Alamosaurus

`--+--Opisthocoelicaudia

`--Saltasaurus

This paper is incredibly detailed, I'm sure that Upchurch now dreams every
night about details of every known sauropod skull. His character matrices
etc. are impressive.

"ABSTRACT -- The phylogenetic relationships of [...] *Nemegtosaurus* and
*Quaesitosaurus* are controversial. Previous studies have interpreted
nemegtosaurids as members of the Diplodocoidea of Titanosauroidea. The
conflicting character sets, which support these alternative hypotheses, are
examined and critically evaluated [British understatement]. Only two derived
states are unique to nemegtosaurids and one or more titanosauroid taxa. At
least five synapomorphies (e. g., transverse narrowing of the rostral end of
the premaxilla, elongation of the subnarial foramen, and extreme retraction
of the external nares) support the inclusion of the nemegtosaurids within
the Diplodocoidea, but the presence of the plesiomorphic state cannot always
be confirmed in higher titanosauroids. [...] *Antarctosaurus wichmannianus*
[...] is placed within the Diplodocoidea (as the sister-taxon to the
Nemegtosauridae) by the analysis. Several lines of evidence suggest,
however, that the holotype of *A. wichmannianus* is composed of an amalgam
of different sauropod taxa and does not represent a reliable operational
taxonomic unit [hence its exclusion from the above cladogram]. The
distribution of derived states indicates a considerable amount of
convergence between the skulls of diplodocoids and higher titanosauroids.
Contrary to previous suggestions, many of the apomorphic features of the
diplodocoid skull were acquired gradually and do not represent a single
complex character [related to rotation of the quadrate]."

"FIGURE 9.   Cladogrrams [sic] of neosauropod relationships, based on the
revised data matrix. _A_, most parsimonious tree produced by analysis I;
_B_, most parsimonious position of *Antarctosaurus* within the
Titanosauroidea; _C_, most parsimonious position for nemegtosaurids and
*Antarctosaurus* within the Titanosauroidea. [...]

_A_ [same as above cladogram, with (*Antarctosaurus* + (*Nemegtosaurus +
Quaesitosaurus*))] 378 [steps]

_B_
+--Phuwiangosaurus
 `--+--Antarctosaurus
      `--+--Andesaurus
           `--+--Malawisaurus
                `--+--Alamosaurus
                     `--+--Opisthocoelicaudia
                          `--Saltasaurus
380 [steps]

_C_
+--Phuwiangosaurus
 `--+--+--Antarctosaurus
      |     `--+--Nemegtosaurus
      |          `--Quaesitosaurus
      `--+--Andesaurus
           `--+--Malawisaurus
                `--+--Alamosaurus
                     `--+--Opisthocoelicaudia
                           `--Saltasaurus
387 [steps]"

According to this paper, the mandible tip and the braincase of *A.* are
probably from separate taxa.