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ABOUT THE REVERSED HALLUX AND...
T. Michael Keesey wrote, >- The only group known to have reversed
halluces (_Avialae_) also appears to
have hyperextendable second pedal digits (at least primitively).<
Hey, wait a minute! Here is a situation where we might best have a look
at the track record.
For example (and there are many), have at look at pages 167 through 173
in TRIASSIC LIFE OF THE CONNECTICUT VALLEY (REVISED) by Richard Swann Lull,
Ph.D., Sc.D,, being Bulletin No. 81, State Geological and Natural History
Survey of the State of Connecticut. Every ichnospecies of Anchisauripus
illustrated (including the trackways of A. sillimani and A. hitchcocki)
shows the mark of a very reversed hallux. The reversal is not quite 180
degrees, and varies from roughly 147 to 158 degrees in those examples
As Swan assures us, the Anchisauripus ichnogenus is unquestionably
Other ichnospecies with a very reversed hallux are illustrated in the
publication, but that well-known example should suffice to make the point
that it is NOT true that the only group known to have a reversed hallux also
have hyperextendable second pedal digits (at least primitively).
The Anchisauripus ichnogenus trackmaker (thought to be the theropod
genus Anchisaurus) has left a clear record of 'four on the floor'.
Specifically, digits II, III, and IV were each firmly on the ground (every
phalanx of each), while it was only the tip (claw) of digit I that touched
the ground, with the proximal end of that digit evidently elevated well
above the ground.
One might conclude that, to use a pun, the Anchisaurus hallux was
'getting around to perching' :), if it wasn't being used for that already.
In this context, note that the tip of the hallux mark extends as far from
the place on the footprint that would be just beneath its location of
origin, as about 70% to 100% of the length of digit II, excluding the digit
II claw mark! (And I'm only talking about its as-seen-from-above length,
which would be appreciably shorter than its actual length.) With that much
reversal and length, one might conclude that digit I is 'coming' (into
usefulness) instead of 'going' (vestigial).
O.K., the ichnological evidence regarding the pes morphology of
Anchisaurus might be variously interpreted, but it should give us food for
thought, lest we jump to unwarranted 'bare bones' (Pun intended.)
Also, I have collected some theropod footprints from the Early
Cretaceous of Maryland with the impression of a very reversed hallux,
including tracks by both non-avian theropods and those of seeming avians,
and none of the specific ones I'm referring to show any signs of a
specialized digit II.
Paleoichnologists might well declare, "Blessed is the substrate that
retains a long memory of those which trod upon it!" :)
"You know my method. It is founded upon the observance of trifles." --
Sherlock Holmes in The Boscombe Valley Mystery