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Meaning of the term "arctometatarsalian"

>To all:
>I am way behind on my terminology ...   What is an arctometatarsalian?

I'll handle this one, shall I?  :-)

Artcus (L.): tight, narrow, compressed, channeled

Arctometatarsalian refers to the unusual structure of the metatarsus (long
bones of the foot) common to ornithomimids, tyrannosaurids, troodontids,
elmisaurids, avimimids, and Mononykus.  In most theropods, the third
(middle) bone is basically cylindrical, and sometimes moderately
compressed.  In the arctometatasalian condition, mt3 is compressed into a
thin bony splint on top, and forms a wedge-like shape at the bottom.  This
condition is believed to be associated with enhanced running ability, in a
paper by, hmmm, let's see...  Oh, yeah.  Me.

P.S.  Confusingly, it also refers to the clade Arctometatarsalia, composed
of ornithomimids, troodontids, tyrannosaurids, and possibly the other
pinched-foot forms.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661