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



Tim Williams <tijawi@gmail.com> 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.

The three taxa of steamer ducks (_Tachyeres pteneres_,
_leucocephalus_, and _brachypterus_) also come to mind as flightless
birds with well-developed pectoral muscles and non-atrophied wings
(Livezey & Humphrey 1986). Interestingly, they use them both for
fighting and for locomotion.


References:

Livezey BC, Humphrey PS 1986 Flightlessness in steamer-ducks
(Anatidae: _Tachyeres_): its morphological bases and probable
evolution. Evolution 40(3): 540-58
-- 
David Černý