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RE: Fwd: Aw: RE: Arboreal Theropods: The prize at the bottom of the cracker jack box
Tim Williams wrote:
>But to argue that this feature was not
>required for roosting in non-bird maniraptorans strikes me as special
>pleading. (_Hypsilophodon_ was once regarded as an arboreal biped
>based on similar flimsy evidence.)
I can't argue that basal paravian anatomy clearly indicates roosting in
elevated sites. But I can prove that some non-flying maniraptorans with no
halluces are obligate tree roosters, even in some of the tallest tree canopies
in the world (Marbled Murrelet hatchlings). Other non - flying maniraptorans
with small, elevated (reaching only to the distal ends of the metatarsus), and
partially or un - reversed, halluces, are facultative tree roosters (Crested
Penguin, Snares Islands). Thus, for you to reframe your argument to exclude
bird maniraptorans, itself, seems to me to be special pleading.
Instead, my speculation relies on their phylogenetic position (directly below
avialans), and their shift to extremely small body sizes.
>The "roosting" hypothesis also holds that "proto-wings" were used by
>maniraptorans to return to earth after roosting. I like the notion
>that "proto-wings" are tied to terrestriality (in this case, returning
>to ground-level) rather than specialized arboreal behavior (for which
>non-bird maniraptorans were clearly not adapted).
>not only do we lack evidence for roosting in non-bird maniraptorans,
>but we have evidence for *not* roosting.
That is a very good point. Yet, among many extant bird families some members
may roost on the ground while others roost in trees. But I agree that wings
probably didn't start out for parachuting. I always liked Hopp and Orsen's
(Feathered Dragons, 2004) hypothesis that they evolved for brooding ground
nests full of eggs and hatchlings. In the roosting hypothesis the possession of
wings by maniraptorans exapted the much smaller basal paravians when they tried
to scramble up to roosts, by aiding in balance and some minor aerodynamic