Re: Picture this time - "titanosauriform" femora

["Jaime A. Headden" <qilongia@yahoo.com>]

Mike Lima (taradosgon@yahoo.com) wrote:

<I cropped several images (mostly from papers) of Diplodocoid and
Titanosauriform femora together into an image highlighting either the presence
or absence of medial deflection and a lateral bulge  and questions.

You can see it at:

http://img294.imageshack.us/img294/6521/femora1nq.jpg>

  Mike, this is a good start, and shows frank testing with a graphical form,
thus cleanly illustrates the question. The reasons usually given are that the
bulge occurs somewhere at or within, but optimizes as a synapomorphy of
Titanosauriformes. The absence of this feature in camarasaurs, for example,
means that Titanosauriformes as a whole can be diagnosed for this feature. What
it does not require is that every titanosaur have this lateral bulge, and it is
certainly possible some taxa (as noted, *Magyarosaurus* could be one of these)
lost this feature, partly as a result of it being a dwarf form, where the
proximally deflected femoral caput and lateral bulge seem related to a
wide-gauge stance, perhaps unneccessary for it's size.

  It is also possible for this feature to be diagnostic even if some other
neosauropods developed it, as in this case those taxa you have noted. Bear in
mind that the diplodocid and dicraeosaurid femora shown do not possess elevated
femoral capiti, though *Limaysaurus* apparently does, and these femoral are
retained at their normal 5-10 degree deflected attitude, while titanosaur
femoral were deflected (everted) more than 10-15 degrees laterally.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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