RE: Serration variation

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> christopher robert noto
> > Isn't it also possible that differences in serrations deal with
different
> predatory tactics and feeding behaviors (like "slice and dice" versus
> "crush and maul")?  Also, have primitive and derived serration characters
> been described in any kind of detail?  Did serrations evolve basally in
> therepods or did the earliest therepods lack serrations?  Could serrations
> be basal to Dinosauria?   Just a thought,
> if this is true and serrations are basal to Dinosauria, can this tell us
> anything about the tooth structure/history  of non therepod
> dinosaurs?
>
Dissertation, anyone?  (Seriously, this is a good potential topic for some
graduate work!)

A good definitive survey of serration structure has not yet been done,
although some aspects of it (serration density, serration function,
serration shapes in Judithian coelurosaurs, serration scratch marks on
bones, etc.) have been conducted (by Christine Chandler, Bill Abler, Jim
Farlow, Dan Brinkman, Phil Currie, Bob Sloan, Aase Jacobsen, Tony Fiorillo,
and others).

I would expect there to be structural differences between shapes of the
serrations of typical ziphodont teeth (big carnosaurs and _Ceratosaurus_)
vs. tyrannosaurids vs. spinosaurids, etc.

Phylogenetics of serration characters?  As a comprehensive survey of the
diversity of these structures within dinosaurs hasn't been conducted, there
is little on which to base such an analysis.  Yet.  Would be a good topic,
though.

Serrations are present in the earliest theropod/theropod-like dinosaurs
(_Eoraptor_, herrerasaurids).  As serrated ziphodont (blade-like) teeth are
present in pseudosuchians and other archosauriforms primitively, they are
almost certainly present in the common ancestor of all dinosaurs.

However, there are a few complications:
I) Teeth of the immediate outgroups of Dinosauria (_Pseudolagosuchus_,
_Lagosuchus/Marasuchus_, _Lagerpeton_) are not described (or known in some
cases).  Furthermore, I don't know of the tooth character (serrated vs.
non-serrated) in basal pterosaurs.
II) At present, basal sauropodomorphs and basal ornithischians are not known
with serrated teeth.  Instead, both clades show much larger denticles.
Using the cladogram Ornithischia + (Sauropodomorpha + Theropoda), it is very
likely that the ancestral members of Ornithischia and of Sauropodomorpha had
serrated teeth (and in fact were carnivorous or omnivorous), and the
denticulate teeth evolved independantly in these lineages.  However, the
alternative (that the ancestral dinosaur had leaf-shaped teeth with big
denticles, and that theropods reverted to the basal archosauriform ziphodont
tooth) is possible.

Hope this helps.


                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
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