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RE: Martin 2004 critique
Mickey Mortimer wrote:
"Protarchaeopteryx has typically avian teeth and there is no reason to
doubt that it is avian." I suppose if maniraptorans are birds in Martin's
mind, that's true enough.
The long primaries of Caudipteryx are said to "so greatly reduce the
usefulness of the hand for grasping that it must imply derivation from an
arboreal flyer/glider." Someone hasn't read Gishlick (2001) I see.
Martin may be on to something here. Allthough it is possible (and maybe
even likely) that the hands could support both a wing *and* continue to be
used as a prey-catching instrument, these dual purposes must have had an
uneasy relationship. Those big feathers sticking out of the wrist and manus
could have interfered with prey capture by the hands, and those same
feathers could get damaged (or bloodied) by struggling prey.
According to Gishlick (2001), the manus lost most of its grasping and raking
ability by the eumaniraptoran stage, courtesy of the great length and
reduced mobility of the manual phalanges. Gishlick proposed that
dromaeosaurids like _Deinonychus_ and _Velociraptor_ siezed and held prey in
a two-handed fashion. This is consistent with the hypothesis that the
larger dromaeosaurids targeted prey of larger or comparable size to
themselves (e.g., tenontosaurs or protoceratopsians). But I find it
different to imagine the usefulness of long, immobile hands in the smaller
maniraptorans. Maybe it is the result of an "arboreal flyer/glider" stage?
"An arboreal stage is further supported by a reflexed hallux on the foot in
all of these forms." Someone hasn't read Middleton's work either.
I can forgive Martin in this case. So far, only a small portion of
Middleton's thesis work has been published:
Middleton K.M. (2001) The morphological basis of hallucal orientation in
extant birds. J. Morphol. 250: 51-60.
Middleton's work on hallucal orientation in fossil birds and non-avian
theropods is also extremely interesting, and I'm looking forward to seeing
it published. According to Middleton's thesis, the notion that basal birds
(such as _Archaeopteryx_) and certain non-avian theropods (such as
_Microraptor_) have a reversed (=opposable) hallux is based on two
assumptions: (1) the preserved orientation of the hallux in a fossil
reflects its orientation of the hallux in life; (2) an elongated and/or
distally-positioned hallux implies that the hallux was reversed. Neither
assumption is supported by the morphology or articulation of the first
metatarsal in these taxa. A true 'perching pes' did not evolve until fairly
late in avialan evolution, well above _Archaeopteryx_.