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Re: Island-dwelling dinosaurs (was Re: Gargantuavis neck vertebra)

Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> Unless Cau is right and Balaur is an avialan, in which case it'd be a great 
> example of a secondarily flightless and large island taxon.

I think the most important thing is not whether _Balaur_ was an
avialan ("bird") or not, but whether it was a herbivore or not.

The vast majority of large, flightless, island-dwelling birds are
herbivores.  Very few are carnivores.  _Ornimegalonyx_, the giant
cursorial owl of Cuba is one possible example, but I'm not sure if it
was flightless.  If not, it was close to being flightless.

The issue of gigantism in island-dwelling birds is also quite
complicated for some lineages.  The moa species of New Zealand
includes some giant forms, such as _Dinornis_; but many other moa
species were not especially large by ratite standards.  It's not known
how large the common moa ancestor was, but individual moa species may
have become larger or smaller as part of the moa radiation.

As for _Balaur_, it was presumably a predator based on the morphology
of the hindlimb, including the dual-raptorial-clawed foot.  However,
even if it is an avialan (rather than a velociraptorine, as recovered
by Csiki &c), then it might not have been secondarily flightless,
because this assumes that basal avialans could fly.  There is evidence
that basal avialans such as _Archaeopteryx_ and _Confuciusornis_ were
incapable of powered flight.

_Balaur_ could certainly have evolved from ancestors that were capable
of some form of aerial locomotion (parachuting or gliding, perhaps
with some rudimentary flapping involved).  But this would hold
irrespective of whether _Balaur_ was an avialan or a velociraptorine.