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Irritator & Archaeornithoides (was Re: Diagnoses)



At 01:52 PM 5/4/98 -0500, Tim Williams wrote:

>Other authors (informally I believe - I haven't seen anything published) think
>_Irritator_ may be more comfortable in the Spinosauria.

Actually, it IS published: in Charig & Milner's _Baryonyx_ monograph, and in
Kellner's review of Brazilian dinosaurs in 1996.

>< Where does Archaeornithoides fit; 

>Considering the presumed ontogenetic stage of the _Archaeornithoides_
specimen, the 
>jaw material may be of negligible phylogenetic value.

I wouldn't say that, but see Charig & Milner's comments about the alledged
similarities between _Archaeornithoides_, troodontids, and spinosaurs.

I suspect _Archaeornithoides_ will yet prove to be a maniraptoriform of some
sort, but more than that is uncertain at present.

>(Is it true that the specimen
>was originally regarded as a coming from an embryo tarbosaur?)

Yes, but before that it was a lizard.

Here's the story, from my point of view:
In a classic paper on baby dinosaurs, Ken Carpenter mentioned references of
"_Tarbosaurus_ hatchlings (pers. commun. R. Estes)".  Since I was getting
started on tyrannosaur limb morphometrics at the time, I was really hoping
to find out details of these hatchlings, in particular their limb measuremnts.

I contacted Dr. Estes, who sent back to me a few slides of a specimen of a
skull of a small theropod.  It had been in the collections at Warsaw, filed
as an undescribed lizard.  Estes had seen it while examining those
collections (for those on the net who don't know the name, the late, great
Estes was one of the greats in the field of paleo-lizard studies, and one of
the first major cladists in American vertebrate paleontology), and
recognized that it was a dinosaur.

In the time between talking to Carpenter and writing to me, he was less
certain that it was a baby tyrannosaur, but he still considered it a theropod.

I filed the slides away, but since all there was was a skull fragment, it
wasn't very helpful for plotting on limb morphometrics.  Some years later
Elzanowski & Wellnhofer published a description of _Archaeornithoides_, and
I thought it looked very familiar.  I got out my old slides, and there it was...

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661