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

[Dann Pigdon <dannj@alphalink.com.au>]

On Wed, Jun 20th, 2012 at 4:50 AM, David Marjanovic <david.marjanovic@gmx.at> 
wrote:

> I'd like to add:
> -- "(except Cassowary)", you write -- yes, what about the cassowaries? 
> How do they (3 species last time I checked) keep their nests from being 
> plundered by goannas too often?

By being complete and utter 'bad-asses' (to use a Holtz-esque phrase). Nothing 
in its right mind 
goes near a male cassowary sitting on eggs. Or with chicks in tow. Or at any 
time really. They'll 
attack anything that dares to look sideways at them.

> -- "Hunt down" isn't a term I'd apply to "nesting sites".
> -- The timing of the extinction of Sparassodonta is not actually known 
> to fit the Great American Interchange, AFAIK. That leaves thylacine vs. 
> dingo as a sample of 1, and even there I have no idea what effect it had 
> that people have been burning much of Australia down every year for some 
> 50,000 years now.

It would seem that most of Australia's large flightless birds were extinct well 
before dingos got into 
the country. Even with dingos-a-plenty for a couple of millennia, emus (and 
cassowaries) are still 
with us though.

Thylacines may not have been any threat at all to the eggs of large flightless 
birds. They 
specialised in eating only soft tissue, and seemed to have avoided tooth 
contact with bone if at all 
possible. The dentition seen in thylacine skulls is generally pristine even in 
very old individuals, with 
little (if any) signs of wear. Attempting to crack open the thick-shelled eggs 
of large flightless birds 
would seem to have been something they'd have avoided. Thylacines may well have 
targetted 
chicks though, and perhaps even adult birds. They certainly had no trouble 
bringing down large 
macropods, so fast-running bipeds with powerful kicks didn't seem to phase them.

One important difference between thylacine and dingo hunting strategies is that 
thylacines seemed 
to have been largely solitary, whereas dingos will hunt in large packs in areas 
capable of 
supporting them. Then again the larger the pack, the larger the area required 
to sustain them, so 
having a concentrated group of ten dingos defending a large territory against 
potential rival 
predators might actually be better for the prey species than having ten 
thylacines patrolling much 
smaller individual territories. Modern ecological studies suggest that rare 
marsupials do better in 
areas where dingos exist than in areas without them, apparently because they 
supress the 
numbers of cats and foxes.

The real question is what impact thylacoleo had on flightless birds. Their 
powerful jaws and 'big-ass' 
shearing teeth (to paraphrase another Holtzism) would seem to make them far 
more likely to 
attempt egg theft than a thylacine. Yet clearly numerous flightless birds 
managed to survive along 
side them for a long time.

Once you throw Megalania into the mix, it would seem that large flightless 
birds are (and were) 
more than capable of dealing with all sorts of nest predators - let alone 
predators willing to target 
the adults themselves. 

-- 
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Dann Pigdon
Spatial Data Analyst               Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj
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