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Re: Moa-Tinamou Clade Found Within Ratites



Ronald Orenstein <ron.orenstein@rogers.com> wrote:

> Rails are probably the best example - seemingly weak flyers that have 
> nonetheless established themselves widely on oceanic islands and have evolved 
> flightlessness
> multiple times (even on islands with mammalian predators, such as Tasmania 
> and New Guinea).


And that's another important aspect about loss of flight in birds: it
can happen in an environment that contains terrestrial predators
(including mammals).  These birds evolve ways of eluding or escaping
predators on the ground *before* becoming flightless.

This is the case for the various neornithean lineages that became
flightless in the early Cenozoic, all of which evolved in a
continental setting in environments where mammal predators were on the
prowl.  Not just the multiple ratite lineages, but birds like
gastornithids and dromornithids as well.

This theme goes back to the Mesozoic.  The flightless bird
_Patagopteryx_ co-existed with terrestrial predators (noasaurids,
crocodilians, snakes) despite being small (chicken-sized) and rather
slow on its feet.  The Ibero-Armorican (Ibero-Occitan) island of the
large (ostrich-sized?) flightless bird _Gargantauavis_ contained
predators (dromaeosaurids, abelisaurids, crocodilians, azhdarchids) as
well - although it's not clear if its ancestors lost flight before
after the emergence of this big island.

In recent times a lot of island-dwelling flightless birds have gone
extinct not so much because of the presence of predators per se, but
because of new/alien predators that were introduced into the
environment (usually humans or animals brought by humans).





Cheers
Tim