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Re: Microraptor also ate fish



Jason Brougham <jaseb@amnh.org> wrote:

> And, Dr. Wiliams, you must completely discredit the finding that Suminia
> could climb into trees, because it does not have the exact same
> adaptations of other animals that climb in trees, and therefore any
> comparison is meaningless. Is that correct?


No, I'm not saying that at all.  _Suminia_ has a whole bunch of
putative arboreal characters: "elongate limbs, intrinsic phalangeal
proportions [including extremely elongated penultimate phalanges of
the enlarged manus], a divergent first digit and potentially
prehensile tail".  The vertebral column is also interpreted as being
highly flexible.  These characters are all found in certain extant
arboreal tetrapods, especially therian mammals.


This is a completely different situation to _Microraptor_.  In
_Microraptor_ there are no morphological correlates of arboreality.
Certain characters that have been regarded as arboreal characters
(grasping pes, claw curvature) could equally be interpreted as
predatory characters.  Perhaps they were used for both?


> And, as a thought experiment, if one day we found evidence that the last
> common ancestor of enantiornithines and ornithurines lacked a reversed
> hallux, what would we conclude? If  enantiornithines developed the
> reversed hallux convergently with ornithurines, then they do not have the
> SAME EXACT adaptation either, it is an analog. In the former it is an
> adaptation of a tarsometatarsus that forms in a completely different, some
> say opposite, way from the latter. Therefore they could not be said with
> any confidence to perch, and citing perching ornithurines would have no
> relevance at all, correct?


As it happens, ornithurans and enantiornitheans do appear to have a
somewhat different kind of perching pes, insofar as the morphology of
metatarsal I is concerned.  Nevertheless, the outcome is the same: an
anisodactyl perching pes.  For _Microraptor_ and other dromaeosaurs,
the digital opposition within the pes is quite different.  It may be
incipient for the anisodactyl perching pes (as Fowler &c propose), but
nothing more.


Look, I'm not saying that the adaptations have to be EXACTLY the same.
 I'm not that much of a pedant.  But when it comes to _Microraptor_
(and other small winged maniraptorans such as _Archaeopteryx_) there
are people that seem desperate to put these guys among the tree-tops.
By contrast, I'm arguing for a sober appraisal of the available
evidence.  No special treatment, just because these taxa just happen
to be close to the line that led to birds.







Cheers

Tim