[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Scansoriopteryx, a non-dinosaurian bird (?)



I agree with most of what Allan says.  Even if
_Epidendrosaurus_/_Scansoriopteryx_ was an arboreal
"tetrapteryx"-style glider has no impact whatsoever on either (1) the
phylogenetic origin of birds from among theropod dinosaurs, or (2) any
ecomorphological or biomechanical hypothesis that invokes a
non-arboreal origin for avian flight.

However, I disagree that _Epidendrosaurus_/_Scansoriopteryx_ shows any
compelling evidence for being an arboreal glider.  Feduccia & Czerkas
point to the "naturally articulated reversed first toe or hallux and
recurved pedal claws, an adaptation exclusive to arboreal perching
animals."  It's obvious that recurved pedal claws are not "exclusive"
to arboreal animals.  (I mean, FFS.)  Also, the first toe (hallux) is
not reversed - Zhang et al. (2002) made it clear that
_Epidendrosaurus_ does NOT preserve a reversed hallux.  Even if it
did, this is irrelevant anyway, because the preserved orientation of
the hallux is as much taphonomic as "natural".  Reversal of the hallux
is determined largely by the shape of the first metatarsal - twisted
or bent in perching birds, to re-orient the toe backward.

The thing that the foot of _Epidendrosaurus_/_Scansoriopteryx_ does
have in common with perching birds is that the hallux (first toe) is
positioned distally on the foot - it articulates at the same level as
the other toes.  However, there is no evidence that this is a perching
adaptation in particular, nor an arboreal adaptation in general.  This
makes the foot functionally tetradactyl in a locomotory sense, as in
therizinosaurs (where it's achieved by a very different pedal
morphology) and _Patagopteryx_ (an incontrovertibly non-arboreal
bird).

Whatever the whopping super-long finger of
_Epidendrosaurus_/_Scansoriopteryx_ was used for, there is no evidence
that it was a climbing aid.  The long finger invites comparison with
the specialized digit of the aye-aye (_Daubentonia madagascariensis_)
and striped possum (_Dactylopsila trivirgata_), both arboreal mammals
that use their long filiform fingers to probe for prey.  But in these
critters this is accompanied by specialized powerful jaws and anterior
teeth to gnaw through wood - obviously lacking in scanoriopterygids.

The manual unguals of  _Epidendrosaurus_/_Scansoriopteryx_ also appear
to be unsuitable for climbing (or predation), because they are only
weakly curved - as noted by Fowler et al. (2011).

As for the "gliding" abilities - the figures alleged to show the
gliding wings are laughable.  Look at Fig. 4 and you're just as likely
to see the face of Jesus as a "propatagium" and "feathers" in the
slab.

Finally, there is the issue of _Epidendrosaurus_/_Scansoriopteryx_
being based on juvenile material, and so potentially unreliable for
inferring too much with respect to either phylogeny and/or the origin
of flight.

That's enough.  Any more comments and I'll have to read the  Feduccia
& Czerkas paper again, and I REALLY don't want to do that again.  Once
was more than enough.  Jeez, what a rubbish paper.




Cheers

Tim


On Fri, Jul 11, 2014 at 2:44 PM, Mickey Rowe <mickeyprowe@gmail.com> wrote:
> Let's try this again in plain text (freakin' gmail thinking anything
> with an e-mail address should have a link...)
>
> The listprocessor is also not recognizing Allan:
>
> From: edels@msn.com
> To: dinosaur@usc.edu
> Subject: RE: Scansoriopteryx, a non-dinosaurian bird (?)
> Date: Wed, 9 Jul 2014 14:59:04 -0400
>
> All:
>
> If we accept that their paper is correct, in that _Scansoriopteryx_ is
> a 'bird', and does not share most non-volant dinosaurian traits, that
> does NOT mean that _Archaeopteryx_ is not the Ur-bird (or close to the
> split), or that all extant birds are NOT derived from non-volant
> dinosaurs - just that _Scansoriopteryx_ is a similar bird-like,
> non-dinosaurian creature, that lived earlier than _Archaeopteryx_.  It
> could be an evolutionary dead-end (as some have opined about
> _Archaeopteryx_ as well).
>
> _Scansoriopteryx_ may have developed its flight from a trees-down
> scenario, but, even if true, this doesn't mean that the ancestors of
> all modern extant birds did.
>
> This is a logical fallacy - "If A is true, that means that B cannot be
> true", when A and B are separate events, and are linked by only one or
> two correlations.   There is no exclusionary situation described here
> (at least based on the abstract).
>
> They believe that _Scansoriopteryx_ is one of the first birds, and is
> not non-volant dinosaurian, and therefore, all other following birds
> are descended from it -  and therefore, birds are not dinosaurs.  (The
> latter being their goal all-along, apparently).
>
> Personally, it would be interesting to see all the so-called
> non-dinosaurian traits that they have identified in _Scansoriopteryx_.
> :)
>
> I agree with them in that _Scansoriopteryx_ may be a so-called "tetrapteryx".
>
> Also, discovery of a pre-_Archaeopteryx_ bird does not mean that birds
> are not dinosaurs.   _Archaeopteryx_ may well be a strange bird ( :D
> ), in that it retained many non-volant dinosaurian traits, along with
> the volant dinosaur traits.  It may be preserving an older lineage
> that is closer to the origin of volant dinosaurs than the specimens of
> _Archaeopteryx_ currently are.
>
> Just my 2 cents,
>
> Allan Edels