RE: Femora of Titanosauriformes: What am I looking for?

[Mike Taylor <mike@indexdata.com>]

Mike Lima writes:
 > Thank you for the help.
 > 
 > But I do have one last question on the subject? Is the
 > lateral bulge characteristic restricted to
 > Titanosauriformes or just maintained by all
 > Titanosauriformes? I.e. all titanosauriform femora
 > I've seen have this trait, but the Dicraeosaurus mount
 > at the Humboldt Museum possesses has quite a bit of a
 > swelling on the lateral margin of its femur (as does
 > the femur figured in "The Dinosauria" to about the
 > same degree as Magyarosaurus) and isn't straight like
 > that of Limaysaurus or Diplodocus. 

Sorry for the late reply ... catching up on some old messages.

The lateral bulge on the femur of titanosauriform sauropods
(i.e. brachiosaurs, titanosaurs and the descendants of their most
recent common ancestor) was first proposed as a synapomorphy of that
clade by Salgado et al. (1997) and seems to have been followed in most
subsequent analyses.  "Synapomorphy" means that it's a novel character
seen in basal members and many derived members, but not in other
sauropods immediately outside that clade; so, no, you shouldn't be
seeing it in diplodocoids such as _Dicraeosaurus_ (nor in
camarasaurs).

However, as is so often the case, there's a plenty of variation and
randomness in this character.  In particular, the lateral bulge that
Salgado et al. (1997: figure 10) illustrated so convincingly using the
femur of _B. brancai_ is not really apparent at all in the femur of
_B. altithorax_ -- see Riggs 1904: plate LXXIV.  It is more prominent
in, for example, the femur of _Apatosaurus louisae_ CM3018 -- see
Gilmore 1936: fig 21.  All in all, I don't think it's the most
convincing character.

(Interestingly, had Salgado et al. coded the two brachiosaurus species
as separate OTUs, then this character would have provided some support
for their otherwise unsupported assertion in the companion paper
Salgado and Calvo 1997 that _B. brancai_ is closer to titanosaurs than
it is to _B. altithorax_.)

Hope this helps.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "I want to create an omelet that expresses the meaninglessness
         of existence, and instead they taste like cheese" -- Marty Smith,
         "The Jean-Paul Sartre Cookbook"


References
----------

Gilmore, C. W.  1936.  Osteology of _Apatosaurus_ with special
reference to specimens in the Carnegie Museum.  Memoirs of the
Carnegie Museum 11: 175-300.

Riggs, Elmer S., 1904, Structure and relationships of opisthocoelian
dinosaurs.  Part II, the Brachiosauridae: Field Columbian Museum,
Geological Series 2, 6, pp. 229-247, plus plates LXXI-LXXV.

Salgado, Leonardo, and Jorge Orlando Calvo.  1997.  Evolution of
titanosaurid sauropods. II: the cranial evidence.  Ameghiniana
34:33-48.

Salgado L, Coria RA, Calvo JO. 1997. Evolution of titanosaurid
sauropods. I: Phylogenetic analysis based on the postcranial
evidence. Ameghiniana 34: 3-32.