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Gatesy et al.'s footprint paper (excerpts)



Gatesy, S.M., K.M. Middleton, F.A. Jenkins, Jr., and N.H. Shubin. 1999.
Three-dimensional preservation of foot movements in Triassic theropod
dinosaurs. Nature 399:141-144.

<  > = my words


"Dinosaur trackways are common in the Orsted Dal Member of the uppermost
Fleming Fjord Formation (Norian-Rhaetian) <Triassic> of Jameson Land,
East Greenland...............strata consist of......units laid down as
part of a large rift lake system..."

"....Although evidence for slight digital approximation <convergence> at
the end of the stance phase has been reported from shallower <dinosaur>
tracks <from other's research>, the elongate Greenlandic tracks document
complete toe convergence, which is retained as a primitive feature among
birds....."

<apparently, when the non-avian theropod raises it's foot out of the
mud, the toes come together.  When the foot comes back down, the toes
splay-out>


"....the posteromedially oriented hallucal print of some <dinosaur>
tracks <from other's research>, which appears superficially comparable
to the impression of the posteriorly directed hallux of birds, has led
<others> to speculation that undiscovered theropods with a reversed
hallux existed in the early Mesozoic."

"We propose that the Greenlandic trackways could have been created by
ceratosaur feet in which the hallux was slightly abducted and flexed,
but not reversed."

"Equating the hallucal entry furrow with the anatomical orientation of
this digit accounts for the erroneous interpretation of a reversed
hallux among early Mesozoic theropod trackmakers."

"The impressions left by stable metatarsi in deep tracks from the
Greenlandic Triassic are independent evidence that these theropods
powered the early stance phase by femoral retraction, rather than by
knee flexion as in living birds."

<so....the big question now becomes, what did it *look* like when a
theropod walked using it's femur more than the bird-like excusions of
the knee/metatarsal/phalanges?  >

As an aside, I note that in the NEWS AND VIEWS section of the same issue
of _Nature_ (p.103-104), commentator Kevin Padian seemed to play-down
the reversed hallux issue (failing to note that Gatesy et al.'s evidence
argued *against* a reversed hallux in any non-avian dinosaur tracks
previously reported).  He did relate, however, that the hallux seems to
have reacted differently from that of birds when the Greenland theropod
raised it's foot.  In fact, if I weren't such an admirer of Padian's
usual academic rigor, I would think that he actually mis-interpreted
Gatesy et al's conclusions re: the position of the hallux. But I
digress...

All in all, I was quite intrigued by the team's conclusions.  It seems
that researchers now need to rethink the whole issue of the evolution of
the theropodan hallux with a bit more care.  When *did* the hallux
reverse?  Maybe it was in the trees after all.  Padian *still* maintains
that Archaeopteryx was not much of a percher (in spite of possessing a
fully reversed hallux), and that true perching came later  (to quote
Kevin from _Nature_:>

"For instance, in Archaeopteryx, which is the first known bird, the
first toe is fully opposable (that is, it faces the other digits on the
same foot), and in later birds the claws enlarge for perching,
suggesting the start of true arboreality." - Kevin Padian.

<So, if Gatesy et al. are correct, and those earlier-interpreted
"reversed hallux dinosaur tracks" *don't* show a true reversed hallux,
then very late adaptation for perching (ala Martin, Feduccia, Olson) may
be the right scenario after all.  But as we all know, none of the new
findings strictly negates the "ground-up" hypothesis at all.>

                                              <pb>