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Re: North by Northwest (was Polar Sauropods )



At 10:37 AM 12/4/98 -0600, Roger Stephenson wrote:
>In Dr. Gangloff's presentation he cited several localities where dinosaur
fossils are abundant.

[snip]

>The following is a listing of dinosaur species positively identified;

Whoa, baby...  Be careful, compilers of lists.  Some of the taxa on the list
can only be identified by a few key (often cranial) bones at the moment.
Some of the forms listed are not in fact "positively identified", but
instead represent common conventions in field identifications. In particular:

>A. Hadrosaurs
>    Kritosaurus - teeth only

I would be interested in how _Kritosaurus_ teeth were recognized to be
diagnostic relative to all other primitive hadrosaurines.  See Horner's 1992
monograph on the cranial morphology of _Prosaurolophus_ (Museum of the
Rockies Occasional Paper No. 2) on the taxonomic problems concerning
_Kritosaurus_.

>D. Thropods
>    1. Tyrannosaurids
>          Albertosaurus - numerous teeth and rare bones

Ugh.  Something that will be corrected in most future faunal assemblage
lists, if I have anything to say about it.  It has been standard operating
procedure for about twenty eight years now to label any mid-sized
tyrannosaurid bones "_Albertosaurus_", and any mid-sized tyrannosaurine
teeth "_Albertosaurus_".  However, the characteristics which identify
_Albertosaurus_ from other tyrannosaurines (_Daspletosaurus_, _Gorgosaurus_,
_Tyrannosaurus_) are cranial, not dental or postcranial.

Mid-sized tyrannosaurid bones could be from young individuals of the really
big forms, or even from aublysodontines.

At present, _Albertosaurus_ is only positively reported from the Horseshoe
Canyon Formation of Alberta.

>    2. Troodontid
>          Troodon - isolated teeth and fragmented skull
>    3. Dromaeosaurids
>          Dromaeosaurus - isolated teeth
>          Saurornitholestes - isolated teeh and vertebra

All three of the above are known from the Judith River, it is true, and can
be distinguished on the basis of their teeth within this unit.  However,
some people have taken the Currie et al. Judith River theropod tooth paper
in _Dinosaur Systematics_ and extrapolated beyond the known sample...  If
this unit (or these units) being studied are outside the Judithian, it might
be safer to regard them as troodontid cf. _Troodon_, dromaeosaurine cf.
_Dromaeosaurus_, and velociraptorine cf. _Saurornitholestes_, at least at
present.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661