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Re: Vegavis gen. nov. - new anseriform in today's Nature




On Thu, 27 Jan 2005, David Marjanovic wrote:

> This may all hold for *Genyornis*, but most other known dromornithids are
> simply older than Australia's oldest grasslands. *Bullockornis*, for
> example, lived in an ordinary tropical rainforest.

Grasses in the Miocene..._Bullockornis_ in the Miocene.
Re: "ordinary tropical rainforest".  This quote is from _Magnifiscent
Mihirungs_, by PF Murray and P Vickers-Rich, (2004) talking about popular
paleontological misconceptions: The vast majority of Australia's
vertebrate fauna evolved in, and were adaptive responses to, scleromorphic
woodlands that grew in any precipitation regime...it is about time we
retired this old rainforest flag." (don't have page number--quate is under
fig. 215).

Several factors relate to why Australia.  Any continental ground-nesting
bird has to either hide or defend.  If it hides it must have an effective
concealing medium (e.g., grass for ostriches).  If it relies on defense it
depends upon how potent the predator regime is.  However, potency in this
resoect does not depend on size necessarily.  Predators of Australia
before the Miocene were, in any case, smaller than their ancestors.
Murray and Vickers-Rich note that egg shells have not been found at most
sites where predators are abundant.  They conclude that nesting sites were
remote from these haunts.  This would make sense.  They also propose
_colonial nesting_ based upon large shell finds, but hedge bt saying these
might be due to fidelity.  In either case, concealment may not have been
primary if predator density/potency was low enough.