Re: ARCTOMETATARSALY

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 05:44 PM 4/1/98 EST, Tetanurae
><<3) The enantiornithine foot, with mt's II-IV fused along full length
>   without pinching or adduction of mtIII.>>
>
>How is this an arctometatarsus?  Maybe Tom can clarify this, but doesn't an
>arctometatarsus require MT III to be pinched?

Yes, arctometatarsality *requires* that mt III is pinched between mts II and
IV, is reduced in thickness proximally, and consequently is less exposed on
the dorsal surface of the metatarsus than II or IV.

Enantiornithine feet are not arctometatarsalian at all.

><<4) Apparently, the alvarezsaurid foot may be a variation on types 1 or 
>   3, or its own type, with mtIII adducted _and_ fused proximally and
>   distally, mtIII appearing only in posterior and distal aspects,
>   totally occluded from proximal and dorsal except at the plantar
>   end.>>
>
>MT III is not just adducted, but it is reduced proximally, like a true
>arctomet pes.  I believe it is so reduced in _Parvicursor_ that it does not
>even reach the tarsus proximally.  

In _Patagonykus_, mt III is not greatly compressed between mts II and IV on
the proximal surface, and is indeed similar to the condition in dromaeosaurs
or oviraptorids.

In _Parvicursor_ and _Mononykus_ (and maybe _Shuvuuia_? Is the foot known?)
mt III is *entirely* pinched out of the proximal region: there is not even a
proximal solid splint.  This "hyperarctomet" condition is also found in the
_Avimimus_ foot.  All that is present of mt III in these forms is the distal
wedge.

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