Re: Noasaurids strike back

["Jaime A. Headden" <qilongia@yahoo.com>]

I would like to point out a few mechanical problems with the idea that the
*Noasaurus* phalanges could hyperflex, as Mickey Mortimer appears to
consider they can. The non-ungual phalanx in *Noasaurus,* PVL 4061, lacks
the ventral "heel" of the proximal articular surface, as in
dromaeosaurids, some troodontids, and of course, the one and only phalanx
known for *Ligabueino* (MACN-N 42); instead, this phalanx in *Noasaurus*
possesses almost _no_ heel but a strip of bone that inserted between the
ginglymoidal condyles of the preceeding phalanx, and had a prominent
rounded articulation for fitting over the dorsal and ventral portions of
that phalanx -- any rotation at that joint would have been relatively
limited and probably only as much as it would take to walk with ... were
it pedal in nature. The ungual, unlike those in dromaeosaurids or
troodontids, possesses _very_ distinct upper and lower lips on the
proximal surface that virtually locks it onto the preceeding phalanx,
which by shape would appear to be the one previously described.
Hyperflexion could not occur in *Noasaurus* if the _only known_ digit was
the digit supposed to do the hyperflexion. Also by extension, the second
metatarsal of hyperflexing theropods usually has an expanded distal
condyle that exposes further on the dorsal surface than it does in other
theropods, to allow the digit to "freeze" in the hyperflexed position,
with a deeper dorsal "pit" or extensor depression than in non-hyperflexing
theropods or in the other metatarsals, to be exact; these features are
lacking in the known metatarsal of *Noasaurus,* which may be the fourth as
well as the second, and which exposes the non-ginglymoidal distal condyle
further flexorly/ventrally than extensorly/dorsally.

  Other evidence offered is the apparently more primitive *Ligabueino,*
which has a single known phalanx that has a distinct set of grooves in the
proximal end that would show a tight articulation with the preceeding
phalanx, and a longer ventral extension of the proximal articular surface
than the dorsal, leading Mickey Mortimer to characterize this as a
"proximoventral heel." In this way, the characterization is fitting given
the nature of the distal end of the phalanx in which the articular
condyles are more prominent above the dorsal half than below the ventral
half of the phalanx is split longitudinally and parallel to the ventral
surface. Unlike hyperflexing dromaeosaurids or troodontids, however, the
lateral ligamental pits are no located further dorsally than at the
mid-point (they are midway between the dorsal and ventral surfaces).
Another feature of the ligament pits is that in dromaeosaurids and some
troodontids, at least, these face dorsally and the dorsal surface of the
phalanx is much narrower than the ventral surface by less than 80%, but
this feature is unknown in *Ligabueino* based on the only published
illustrations, of which the description is non-enlightening. Whithout a
metatarsal or other phalanges (or for that matter, articulation) this
phalanx is largely uninterpretable, and using a large ungual-phalanx ratio
as in *Noasaurus* to support referral of the digit to the foot, or even
referring the phalanx in *Ligabueino* to the foot, would seem highly
suspect at this point. Rather, this phalanx should be treated as an
anomalous phalanx and not neccessarily applying to the pes, nor does the
data for it being hyperflexing very strong, though likely based on the
total data.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


        
                
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