Re: Microraptor also ate fish

[Tim Williams <tijawi@gmail.com>]

Gregory S. Paul <GSP1954@aol.com> wrote:

> -- Velociraptor does not have a flattened central finger to firmly anchor
> the more important distal primaries that microraptors do. The presence of
> flight features in large derived dromaeosaurs is the same pattern seen in
> secondarily flightless birds. It has never been shown that these features 
> evolved
> before flight, they are very probably the result of flight.


I'm not convinced that the flattened central finger evolved as a
flight-related feature.  Then again, I'm not convinced that it's not.
For theropod taxa at the non-flight --> flight transition, it's
difficult to sort novel characters that evolved for powered flight
from pre-existing characters that were exapted for powered flight.


> -- The big dromaeosaurs did not have arm muscles as proportionally large as
> those of microraptors because the former have smaller arms (the humerus is
> half the length of the body in microraptors, much less so in Velociraptor)
> with smaller muscles. Only the Jehol dromaeosaurs have arms large enough to
> be muscled well enough for powered flight (maybe juveniles of big
> dromaeosaurs had some flight ability, would be nice to have some skeletons to 
> see what
> is going on with them).


The forelimbs of _Microraptor_ are actually not that long.  The
humerus/femur ratio is around 0.8, and the manus/femur ratio is only a
bit higher than 1.  Lower than _Archaeopteryx_ (h/f = 1.1-1.2; m/f =
1.4-1.6) and even _Anchiornis_ (h/f = 1.04; m/f = 1.6).  The ratios of
_Microraptor_ are actually very close to those of the indisputably
non-volant and non-arboreal basal troodontid _Eosinopteryx_.


> -- MY understanding is that the Jehol flora was conifer dominated and
> closed canopied, so there were mainly high canopies rather than cycad type 
> fronds
> to fly up into.


Yes, that's my understanding too.  But I'd bet that the seeds
preserved inside _Jeholornis_ came from some kind of cycadophyte, not
a conifer or angiosperm.  (Maybe the things inside _Jingengopteryx_
too.)  I'd also bet that many small maniraptorans were eating
cycadophyte fructifications, and needed some way to get up (and down).


> -- Keratin sheathes are never preserved in large dromaeosaurs, but the
> chance that they were as curved as those of microraptors is zero. All small
> terrestrial theropods and Mesozoic with preserved toe claw sheaths are low
> curvature, and no known bird incl raptors that spends much time walking and
> hunting on the ground has such strongly curved toe claws. The central toe 
> claws
> of Veloci and Deino would have been fairly flat and probably tip worn, like
> those of ratites and secretary birds


This strikes me as circular reasoning.  Without knowing the claw
curvatures of large dromaeosaurs, we can't say whether these extreme
curvatures in _Microraptor_ were exceptional or not.


> -- Again, no bird that moves much on the ground has strongly curved toe
> claws, they are always flattened. No known exception. The strongly curved toe
> claws of microraptors mean they were not habitual ground walkers. The big
> foot feathers would not be good for that either. Could do it if they needed 
> to,
> but they were not adapted for it.


The idea that the big metatarsal feathers prevented or impeded
terrestrial locomotion is a total crock.  They certainly would have
impeded running, but that wouldn't be a problem if you're in an
environment where running wasn't really an option anyway.

Yes, large hindwings could get snagged in ground vegetation.  But this
would be no less of a problem in a canopy - where the animal is
*surrounded* by vegetation.






Cheers

Tim