Re: "Heel to Toe"

["Ray Stanford" <dinotracker@earthlink.net>]

Mickey Mortimer said:

----- Original Message -----
From: Mickey Mortimer <mickey_mortimer@email.msn.com>
To: <dinosaur@usc.edu>
Sent: Wednesday, February 02, 2000 12:16 AM
Subject: Re: "Heel to Toe":



Quadrupedal dinosaurs also had a digitigrade stance.  In the case of
sauropods and stegosaurs, for instance, the foot appears plantigrade because
there is a large fleshy pad underneath the metatarsus.  Actually, the
metatarsus is lifted off the ground and the dinosaur is thus digitigrade.
Other quadrupedal dinosaurs with more "normal" feet (prosauropods,
Scelidosaurus, ankylosaurs, iguanodonts, hadrosaurs, neoceratopsians) had
digitigrade feet just like their bipedal counterparts.  Also, I don't think
"heel-walking" was very common among bipedal dinosaurs, it is simply known
from a few tracks.

    --------

    My (Ray's) response: In a sense you are right, but I don't think you and
I are using the same definitions of the term "digitigrade".  In my terms,
when the metatarsals are supported on a fleshy pad (as you correctly point
out) they are in fact plantigrade or, perhaps more realistically,
QUASI-plantigrade.  Why?  Because the metatarsals are not ELEVALED by
muscular action, and are basically supported on fleshy pad(s) that transfer
pressure to the ground, and, thus, the animal is clearly, unquestionably
walking on more than his toes (thus, NOT digitigrade, which, of course,
refers to walking or standing ON THE TOES ALONE).

    Also, I have collected in the Early Cretaceous of Maryland two pes
prints that Martin Lockley and others others who have examined them feel may
very possibly having been made by Nodosaurs.  One is a pes/manus set,
produced by a very small animal (pes print only 25 mm across), while the
other, a solitary pes print, is, in contrast, 28 cm across and essentially
identical to the aforementioned tiny pes print, except that it has much more
detail of the PAD STRUCTURE(s) that produced the imprint. And, yes, the
metatarsals appear to have been somewhat elevated, but not (judging from the
bone-through-pad pressure patterns) elevated very much.  I think that
sometimes examination of impressions left by an animal's actual foot can
show us that things were a bit different from what might have been concluded
by study of bone structure and deduced juxtapositions, alone.

    Another on-list respondant, archosaur@usa.net, has wondered whether
there was actual plantigrade progression at all.  The answer is an
unquestionable YES.  In fact the legendary "man tracks" from the Paluxy
River bed in Texas are clearly the result of a bipedal dinosaur which had
lowered its feet into plantigrade (metatarsals down) positions, thereby
increasing the area of contact with a very soft walking surface and gaining
added support against sinking so deeply.  In the instance I have in mind, we
can clearly observe that as the dinosaur proceeded plantigrade UP-SLOPE, the
metatarsals were gradually elevated (as the surface became firmer) into,
finally, the normal digitigrade progression.  I can also conceive of a
dinosaur deliberately LOWERING ITS VISIBLE PROFILE (by lowering into
plantigrade pogression) while, say, trying to sneak away from some perceived
threat.

    Those of us engaged directly in track studies know that the older books
are wrong in suggesting that plantigrade progression is exceedingly rare.
Yes, it is of course vastly less frequent than examples of digitigrade
progression, but from examining both the track evidence here (from the Early
Cretaceous of Maryland) and much of the available literature, it is clear
that on a world-wide scale, examples are surprisingly abundant.  There are
in fact some nice examples of plantigrade impressions that can be seen right
in my living-room museum. In one case the animal seems to have been
progressing at a moderate speed in plantigrade fashion, while turning!

    At this point in my track studies, it seems that plantigrade foot
positions may occur more frequently in certain ornithopod populations, than
in theropod populations, yet that tentative observation may be biased by
limited sampling or by local paleo-environmental factors.  I should admit,
however, that the most beautifully detailed plantigrade track I have ever
found (or ever seen depicted for that matter) is very possibly that of a
theropod.

    And now, I must progress, plantigrade, to bed.  If there are boo-boos in
this, it is because the time is 2:08 AM, locally, of course.  :)

    Ray Stanford