Re: Defining Characteristics of the Titanosaurids

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Patrick Johnson wrote-

> I think that one thing I have straight is that all titanosaurids have
caudal vertebrae whose form puts them
> apart from other sauropods. (I seem to find the shape of the caudal
vertebrae well described in the book
> Dinosaurs of Utah by Frank DeCourten, University of Utah Press, 1998. But
this is only in reference to
> Alamosaurus.)

Because Titanosaurus is thought by many to be indeterminate (Wilson and
Upchurch, 2003), the ICZN does not allow a family level name to be based on
it.  The group equivalent to the classic Titanosauridae is now called
Titanosauria.  Procoelous proximal caudal centra are one synapomorphy of
titanosaurs.  Others listed by Wilson (2002) in his recent analysis of
sauropod phylogeny include-
- Cervical pneumatopores (pleurocoels) undivided.
- Posterior dorsal neural arches lack hyposphene-hypantrum articulations.
- Anterior and middle caudal centra with ventral longitudinal hollow.
- Absence of forked chevrons.
- Deep haemal canal.
- Crescentic sternal plates.
- Ulnar olecranon process prominent.
- Ischial blade platelike, no emargination distal to pubic peduncle.
- Distal tibia expanded transversely to twice midshaft breadth.
- Osteoderms.
However, it must be noted Wilson did not include the most primitive
titanosaur Andesaurus, nor did he include any non-titanosaur
titanosauriformes except for Brachiosaurus and Euhelopus.  So some of the
above characters probably developed a bit before Titanosauria, and others a
bit after Titanosauria.

> Some of my sources claim that all titanosaurids were armored. But I have
come to the conclusion that this
> can only be said for certain in the case of Saltosaurus.
> Am I right or wrong about this?

Some titanosaurs (Agustinia, Ampelosaurus, Lirainosaurus, Magyarosaurus,
Malawisaurus, Mendozasaurus, Neuquensaurus, Saltasaurus) were armored, while
others (Alamosaurus, Epachthosaurus, Isisaurus, Opisthocoelicaudia,
Rapetosaurus) were not.

Mickey Mortimer