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Re: Microraptor hanqingi, new species from China.



Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> Much like how the IVPP team insists on calling theropod manual digits 
> I-II-III II-III-IV, despite the fact the rest of the theropod community is
> unconvinced by their arguments.  Though as the hangingi paper (who wants to 
> bet it's just another M. zhaoianus?) is authored by BANDits and ABSRDists, we 
> really shouldn't expect them to read counterarguments to their positions 
> anyway.


They do more than just fail to acknowledge counter-arguments.  In some
cases they actually misquote contrary evidence to give the impression
that it actually supports their own arguments.  For example, the
authors make this bold assertion regarding the purported arboreal
adaptations of _Microraptor_:


"The morphology of the foot indicates an arboreal habitat; the hallux
is posteriorly
positioned (Xu et al., 2000; O’Connor et al., 2011) and capable of
opposing the other
toes;"


Wrong.  The two studies cited (Xu et al., 2000; O’Connor et al., 2011)
clearly state that the hallux of _Microraptor_ is *distally*
positioned, not *posteriorly* positioned.  This is a big difference.
The pedal digit I of _Microraptor_ has migrated distally, such that
the hallux is lower on the foot compared to the ancestral theropod
position.  (This is also seen to varying degrees in other
dromaeosaurids; Fowler et al. [2011] interpret the more distal hallux
of _Deinonychus_ as a predatory adaptation, not a perching
adaptation.)  Having a distally positioned hallux puts this toe closer
to the level of the other three toes; it does not in itself confer a
perching/grasping foot.


Neither Xu et al. (2000) or O’Connor et al. (2011) claim that the
hallux of _Microraptor_ was positioned posteriorly (i.e., reversed)
such that it could effectively oppose the other three digits (i.e.,
reversed digit I opposes digit III, for an anisodactyl perching foot).
 In _Deinonychus_, digit I is somewhat medially directed such that it
might have acted in opposition to digit IV (Fowler et al., 2011).
This was likely true for _Microraptor_, but this is a very different
pedal configuration to that required for perching.


Gong et al. also take liberties with Middleton's work on hallucal
orientation.  Also from the _M. hanqini_ paper:


"Middleton (2003) examined the holotype of _Microraptor zhaoianus_ and confirmed
that metatarsal I lies in a position behind the tarsometarsus but
considered this a nonperching
foot since he could not see if the metatarsal was twisted."


This is not really what Middleton said.  Middleton merely borrows a
quote from Xu et al. (2000) ("Pedal digit I is preserved on the
posterior surface of metatarsals II-IV").  In _Microraptor_, as in
_Archaeopteryx_, the posterior position of the hallux is a
preservational artifact, rather than reflecting a reversed position in
life.  Middleton goes on to say: "I find no compelling reason to
assign a perching morphology to the foot of _Microraptor_ without more
definitive skeletal material".  Well, further material fails to find
any evidence of a perching foot in _Microraptor_: the shaft of
metatarsal I is straight, with no torsion or bending.  Gong et al.
actually concede this last point, but nevertheless go on to say:


"Although one of us (Martin, 1991) was the first to point out that
modern perching birds
had a twisted metacarpal I [sic] , we do not expect to find this
condition in the progenitors of
perching birds and suspect these animals were using a variety of
perching mechanisms."


Based on what comes later in the paper, Gong et al. seem to be saying
that a perching foot was achieved by way of the enlarged second toe:


"It [the second toe] may have opposed the claw on the
first digit (reduced but with an enlarged claw sheath) and perhaps
also the fourth digit
which is able to swing laterally and is often preserved in that
position in the specimens so
that the foot could firmly grip branches."


No evidence is offered in support of this interpretation.  The gross
morphology of the _Microraptor_ foot actually weighs against perching
abilities of any kind.  Although the first toe of _Microraptor_ has
shifted distally (not "posteriorly") it is still fairly short, and
definitely non-reversed; the ungual phalanx of digit I does not
protrude any further distally than metatarsal III.  It is highly
doubtful that the hallux could "firmly grip branches."  Having the
second and fourth toes capable of opposing one another is also pure
speculation.  As "perching mechanisms" go, the pedal morphology of
_Microraptor_ is woefully inappropriate for perching.


Of course, the broad theme of the Gong et al. paper is to reconstruct
_Microraptor_ as a colugo-like arboreal glider.  So the authors have
to find some way to convince others (and themselves) that this critter
was adept at moving around in trees.  Most of the claimed "arboreal"
adaptations have been dealt with by Dececchi and Larsson (2011).
Personally, although I think that there was some parachuting or
gliding behavior involved in the evolution of avian flight, I'm
unconvinced that winged paravians like _Microraptor_ or
_Archaeopteryx_ glided from tree to tree in the manner of colugos or
flying squirrels.  The scenario I favor is that these particular
paravians (and their close relatives, the direct ancestors of birds)
climbed only occasionally, such as to obtain food, and used their
wings to get them back to earth safely.  (This might also explain the
subarctometarsalian pes of _Microraptor_, evolved as a shock-absorber
during landings... but I don't want to push this idea too far without
evidence.)  In any case, _Microraptor_ and _Archaeopteryx_ do not fit
any definition of "arboreal".







Cheers

Tim