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Ditto for squirrels.
 >
 > But there was next to nil quartz sand in the Solnhofen carbonate
 banks.  It
 > was mostly a limey mud.  Carbonates, especially as mud, would have
 very low
 > Mohs hardness.

True enough, but it also provides less purchase for movement,
and so promotes slipping and the like. [Lime mud is notoriously
slippery].  This might 'compensate' for the lack of hardness
(if Archi even spent much time on such a treacherous surface).

 > This is probably true for Sinornis' lineage.  However, almost all
 other
 > Mesozoic birds (Icthyornis, Hesperornis, Patagopteryx, the
 > Enatornithoformes, etc.) are demonstrably nonarboreal.

These are all very specialized forms, anatomically speaking,
so they are hardly likely to be characteristic of the earliest
birds.

[The fossil record of birds is deomnstrably worse than of any
other boney organism, excpet perhaps small theropods].

 > Thus, Sinornis shows
 > that birds were capable of evolving arboreal forms, but is
 phylogenetically
 > distant from the common ancestor of modern perchers/tree dwellers.

Probably, but so were the aquatic forms you listed!

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.