Basal tetanurines (was RE: Ruben Strikes Back)

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

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> ekaterina amalitzkaya
>
> In Sereno's Science review he makes an interesting statement that the
> ancestral tetanuran might have been a large bodied predator.

Actually, others (such as myself) have been saying the same for a few years.

> If we accept
> this a size compression occurred only along the coelurosaurid
> line and may
> be this was the selective force for the origin of
> feathers/insulation. And
> in Gouldian wording flight may almost be an exaptation or a
> spandrel. Do the
> experts uniformly support a size compression along the
> coelurosaurid line or
> is just an artefact of sampling.

Very difficult to tell.  All the best known basal tetanurines are fairly big
animals (_Megalosaurus_, spinosaurids, _Torvosaurus_, _Piatnitzkysaurus_,
_Eustreptospondylus_), basal carnosaurs are fairly big (_Cryolophosaurus_,
_Monolophosaurus_, sinraptorids), and at least some basal coelurosaurs
(_Dryptosaurus_, _Deltadromeus_) are, too.

However, there are small forms (such as _Iliosuchus_ and the late lamented
_Podokesaurus_) who cannot be firmly assigned to either Ceratosauria or
Tetanurae.  They could concievably be  small basal tetanurines.  Also, some
basal coelurosaurs (_Ornitholestes_, _Proceratosaurus_, _Coelurus_) are
smaller animals (although not as small as, among others, compsognathids).

> Are the tyrannosaurs secondarily
> re-enlarged then?

Almost certainly!  Basal tyrannosaurids are fairly big for coelurosaurs, and
almost all recent studies put them among Maniraptoriformes: the primitive
members of most of the other maniraptoriform clades are small forms.

> Would forms like Deltadromeus represent the primitive large
> bodied state of
> coelurosaurs?

May well be.

>If the contraction is for real may be the coelurosaurs
> emerged from an island dwarf population that swept the world (just a
> speculation).

Actually, there is a guy who works on bats at the university who suggested
the same thing to me...  However, it would be extraordinarily difficult to
test at present.


                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
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796