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



I was under the impression that the placentals-beat-marsupials argument had 
been pretty well rejected, with evidence that the reverse may have happened on 
Australia. 

Ronald Orenstein 
1825 Shady Creek Court
Mississauga, ON
Canada L5L 3W2

On 2012-06-19, at 9:24 AM, John Bois <mjohn.bois@gmail.com> wrote:

>> Am 18.06.2012 um 17:53 schrieb Brian Lauret:
>> What we consider to be normal weaknesses and behaviour for flightless birds 
>> on islands may not be particularly applicable to flightless birds that 
>> evolve on continents rarer though they may be.
> 
> Two things worth considering:
> 1. Some continental habitats are like islands inasmuch as nesting
> large flightless birds can enjoy low predator density. Highest
> concentration of ostriches occurs in the more arid sections of savanna
> grasslands. Indeed, all continental large flightless birds (except
> Cassowary) depend on expanse of grassland for nesting.
> 
> 2. Not all predators are created equal. A still-open hypothesis is
> that placentals have a predatory edge over marsupials. The latter are
> handicapped by their ontogeny particularly in the sensory and social
> domains, i.e., their brains have less time to develop before basic
> structures must be laid down in order to make trek to pouch. So niches
> that worked before presence of placentals may have been islands
> (excuse the phrase) of low predator ability. Without doubt, thylacines
> were fearsome animals. However, they may not have been as clever at
> hunting down large flightless bird nesting sites as their placental
> counterparts.