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toes and metatarsals in the Ornithodira



>Thomas_R_HOLTZ@umail.umd.edu
><<Take a look at the feet of Herrerasaurus sometime.  And, while 
>you're at it, the feet of basal lineages within the Ornithischia.  Now, 
>see what the probable foot of the ancestral dinosaur looked like.  
>That's right, Digits I-IV as functional toes, digit V already reduced.  
>For a little outgroup analysis, try the feet of basal pterosaurs and 
>other ornithodirans.>>
>
>    Once again call to "The Dinosauria".  Figures 4-2 B, 15-8 G~L, 15-7 P,
>and 18-2 G; Depicting the pedes of _Herrerasaurus_, 
>_Anchisaurus_, _Sellosaurus_, _Yunnanosaurus_, _Blikanosaurus_, 
>_Riojasaurus_, _Plateosaurus_, and _Segnosaurus_ respectively.  
>As can be seen, the pes of _Herrerasaurus_ bears a long and fairly 
>robust metatarsal V with a fairly large phalange; while the pedes of 
>the various prosauropods and of _Segnosaurus_ bear medium length 
>to short metatarsal V with a very small or non-existant phalange.  
>The pes of _Segnosaurus_ is most similar to the pedes in 
>_Anchisaurus_, _Sellosaurus_, and _Riojasaurus_.  Taking your 
>advice Dr. Holtz, you have proven to me once again that Segnosaurs 
>are not theropods or Herrerasaurs because their feet most resemble 
>the feet of prosauropods.

If you notice, my point was about the whole digit, but not the metatarsals.
I'll address this below.

>    While we're at it, _Segnosaurus'_ pes also strongly resembles
>_Scelidosaurus'_ (fig. 20-3 C), while neither one bears a closer resemblance
>to _Herrerasaurus_ than they do to each other.
>    Basal Pterosaurs have five fully developed digits as do Brontosaurians.

Actually, the former is not true (in the sense of digits used in
locomotion).  In Schleromochlus and later pterosaurs, mtV is short and
robust, and the phalanges (where present) are nonlocomotory.  MtI-IV, on the
other hand (er, foot), are subequal in length and have functioning toes (as
do the feet of many other ornithodirans).

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
Phone:301-405-4084