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Re: Ah ha! That's where therizinosaurs came from

 Contra Dececchi & Larsson (2011), small maniraptorans didn't need to
 be highly arboreal in order to climb vegetation, or to be capable of
 "trees-down" aerial descents.

So far, so good...

 Has anyone considered that the reason
 why certain non-avialan paravians had gliding adaptations was
 *because* of their poor arboreal abilities?

I don't understand that. All I can imagine are adaptations to _parachuting_ if they were capable of climbing up but not down.

Arms that cannot be lifted above horizontal do look more suitable for gliding than for flapping and maybe even for climbing, the lack of tertials in *Archaeopteryx* is the outright opposite of what I'd expect of a glider or of an animal with recent gliding ancestry. And while this wouldn't be too detrimental in a parachuter (as shown by the "flying" frogs), asymmetric, lift-generating feathers don't fit parachuting well.

> Never mind nest robbers. It now seems that the flightless
> paleognaths became flightless in the early Paleocene on the
> continents as if they were islands -- due to the lack of big
> predators after the K-Pg mass extinction.

 Agreed. And not just palaeognaths. Several basal neognath lineages
 also spawned large, flightless birds at around the same time -
 dromornithids, gastornithids (diatrymids),


 sylviornithids. This
 last one (_Sylviornis_) was found only on New Caledonia, and became
 extinct relatively recently. But like the ratites, dromornithids
 and gastornithids, the superficially ratite-like _Sylviornis_ appears
 to represent a faily ancient flightless lineage.

Oh yeah... I had forgotten that *Sylviornis* is not an overgrown megapode anymore.