Re: Lack of Running Giant Theropod Tracks

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

On Fri, Dec 3rd, 2010 at 1:06 PM, Augusto Haro <augustoharo@gmail.com> wrote:

> 2010/12/2 Sim Koning <simkoning@msn.com>:
> >
> >  Adult tyrannosaurs, although slower, would have been able to kill 
> > ceratopsids and 
ankylosaurs,
> animals that the juveniles may have been too weak and blade-toothed to 
> exploit. However, 
making a
> living by attacking something that is not only your own size, but also able 
> to kill you as easily
> as you could kill it, may not have made for a very survivable lifestyle.
> 
> This does not seem easy to infer. For example, the weaponry of a rat
> or squirrel (their incisors) make them probably very dangerous for a
> similarly sized predator, yet many weasels make a living mostly of
> eating these similarly sized rodents...

Indeed; many carnivores regularly take on potentially dangerous prey. Lions 
will target Cape 
buffalo, even though they could look for easier prey if safety was their 
primary concern. Yet 
experienced lions still target such dangerous prey, because the potential gain 
from killing such a 
large creature often outweighs the increased risk. I think the key word there 
is 'experienced' 
though.

Recent studies in sub-adult Great White sharks suggest that their jaw bones 
aren't strong enough 
for them to tackle large mammalian prey properly until they reach about 3m in 
length:

http://www.abc.net.au/science/articles/2010/12/02/3083105.htm

This doesn't stop them from attempting such attacks; however they tend to abort 
after just one 
exploratory bite. The danger to the shark isn't from the prey harming them in 
defense, but in the 
shark's jaw muscles breaking its own jaw in the attempt to feed. I imagine a 
juvenile tyrannosaurid 
might suffer a similar fate trying to subdue a well-armoured thyreophoran, 
whereas a much older 
individual may have had the necessary equipment to power through that armour. 
The potential 
dangerousness of the prey may have been a secondary concern.

Also keep in mind that people tend to think of the huge 12m tyrannosaurs as 
'adults', and anything 
smaller as 'sub-adults'. If tyrannosaurs continued to grow throughout their 
lifetime, as modern 
crocs do, then they may well have reached sexual maturity (ie. 'adulthood') at 
much smaller sizes. 
The 12m long behemoths may have just been unusually long-lived individuals, 
rather than 
representative of the normal adult state.

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