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

David Marjanovic <david.marjanovic@gmx.at> wrote:

> When crown-group birds (other than penguins and plotopterids!) become
> flightless, their forelimbs become useless (except sometimes for activities
> like display that require very little muscle power), so the bones that
> anchor their muscles atrophy.

_Xenicibis xympithecus_, the flightless ibis of Jamaica, also shows no
such profound atrophication.  Here long forelimbs were retained as a
weapon.  The furcula, coracoid and sternum were all well developed,
and the club-shaped hands were capable of delivering a hefty blow.

Because there are a great many birds that employ their wings as
weapons, it is perhaps not surprising that certain flightless birds
retained wings for this purpose, along with a substantial degree of
muscle power.  In the Rodrigues solitaire (_Pezophaps solitaria_) the
wings are truncated, but nevertheless equipped with a terminal 'knob'
as a weapon.  _Xenicibis_ appears to be exceptional (among birds) in
that the forelimb became highly specialized as a weapon.  I wonder if
this was the case for certain non-avian theropods too.