Titanosaurs: the Ducks, Dogs, and Horses of the Cretaceous

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

Okay, everybody knows the old saying, "if it looks like a duck, quacks
like a duck..." then it's a Titanosaur.

  Unfortunately, titanosaur anatomy is expansive, and within the single
group, much development and evolution has occured. Look at the camarasaur
like skull of *Malawaisaurus*, the diplodocid-like skull of
*Rapetosaurus*, and the brachiosaur-like skulls of some of the later,
"higher" titanosaurs to be described. You've seen the skulls, of course.

  Okay, so titanosaurs are wierd. There are three general classes of them.
The most basal look like camarasaurs. Well, duh ... think about it. Unless
one thinks that titanosaurs went *poof!* and there they were, titanosaurs
developed from _something_. The most basal animal will look like the
closest sister group, invariably; this has led people to presume that
basal animals might belong to polyphyletic assemblages of some basal
radiation, or to groups of similar form, but more primitive. Remember
Thecodontia?

  The postcrania in titanosaurs does not change much, but when it does, it
is typically in the axial skeleton. The cervical anatomy is different in
*Malawisaurus*, *Rapetosaurus*, *Saltasaurus*, and *Titanosaurus
colberti*, but still incorporate a few constants, including the internal
somphospondylous nature, expanded and "simple" surfaced neural spines
without fossae in the sides. This progresses into the dorsal verts. The
pleurocoels of all camarasauromorphs are simple and relatively not divided
until the higher brachiosaurids, such as *Brachiosaurus* and
*Sauroposeidon*. Caudal anatomy is much more plastic in titanosaurs,
including wide caudals in *Pelligrinisaurus*, fused chevrons and caudals
in *Phuwiangosaurus* and *Opisthocoelicaudia*, and attenuated and low in
the saltasaurines....

  If one thing that titanosaurs have taught me, it's that there are few
constants within the group. There are almost no constant cranial features
in titanosaurs. Even teeth change in evolution. What are truly consistent
within titanosaurs are the appendicular and specific caudal features,
pretty much not much to do with how procoelous they are, etc.... For
instance, the manus and the ulna are distinctive, the pelvis, and the
scapula are distinctive, but largely it's in the ulna and the coracoid.
For all these, except the cervical vertebral neural bifidy and the caudal
vertebral opsithocoely, *Opisthocoelous* is a classic titanosaur.

  One does not find just one bone, and say that no matter what else is
attached to this and what it looks like, that bone belongs to a so-and-so
group of dinosaurs. One does not ignore parts of an animal, in other
words, to favor distinctive other parts.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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