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Re: Lack of Running Giant Theropod Tracks

On Nov 28, 2010, at 1:49 PM, Don Ohmes wrote:

>> So if there was a drop off in speed (loss of the ability to run) when a 
>> carnosaurs/tyrannosaurs reached giant sizes, I'm left wondering why having 
>> your prey options limited to the most dangerous herbivores in your ecosystem 
>> would have been an advantage.
> Again, I assume you mean sauropods. I am flabbergasted every time this 
> comes up on list, and I mean nothing personal in this. Everybody seems 
> to agree w/ you, but can offer nothing to defend this intuition become 
> an institution.
> Try a thought experiment -- drop down on all fours and become a 
> sauropod. Your neck is now as long as your torso, and as big around as 
> your finger, or maybe something a little more sensitive. How big is your 
> head? Really, really, small...

While a thought experiment such as this may seem intuitive, the reality is that 
large vertebrate predators in modern systems rarely attack prey many times 
larger than themselves, unless the predator is a powered flyer or a pack hunter 
(yes, we can find a long list of one-off anecdotes and the like that show the 
occasional exception, but they are rare).  Regardless of mobility, potential 
vulnerable anatomy, and other factors that we might expect to be major 
determinants, the observation is that size matters a great deal.  The patterns 
are different for some invertebrates (especially r-selected arthropods and 
mollusks), but for terrestrial vertebrate predators, even very well-armed taxa 
rarely make a meal of animals much larger than themselves hunting solo.  

In terms of surprise, I find myself personally surprised at the continued focus 
on predation of adults, given that our current knowledge of dinosaur 
reproduction strongly implies that there was a vast biomass of juveniles 
present for many species.


--Mike H.

Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181