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Re: cause of Gigantism in sauropods

I've heard that bobcats sometimes take down mule deer. A quick web search turned up this:


-----Original Message----- From: Habib, Michael
Sent: Monday, February 07, 2011 1:11 PM
To: vultur-10@neo.tamu.edu
Cc: dinosaur
Subject: Re: cause of Gigantism in sauropods

On Feb 7, 2011, at 12:45 AM, <vultur-10@neo.tamu.edu> wrote:

So in the Morrison, the sauropod-theropod size gap seems smaller than the elephant-lion one. I see little reason to believe that Saurophaganax or A. maximus could not take down even Giraffatitan or Supersaurus.

Neat comparison with the body mass estimates (thanks for punching the numbers!) but I'm not sure I quite agree with your conclusion. It seems reasonable that something like Saurophaganax could take down something like Giraffatitan under very rare, extreme circumstances, just as living terrestrial macro-predators (or groups of them) very rarely kill much larger animals than themselves. However, I see no reason to expect that such events were common, or even occurred with a high enough frequency for us to seriously consider them as major factors in our reconstructions of Mesozoic ecology. Living terrestrial vertebrate predators rarely take prey even three times their own mass, much less 6-8 times.

The elephant-lion size ratio probably does not represent the ratio at which predation is regular or ecologically important; at best it is a ratio at which a very rare predation event is still barely feasible - and that is for a specific guild of predators and herbivorous mammals. The more important size ratio is the maximum predator:prey mass ratio among *regular* predation events. Phrased as a question: Of those large terrestrial animals that are predated as adults with a high enough frequency for its impact on total population mortality to be measurable, how large are their smallest predators (or total mass of packs, if they are predated by groups)?

I don't know exactly what the answer to that question is, but qualitative observation suggests that the size gap is pretty small. The vast majority of predators, even large ones, mostly take prey smaller than themselves. Even animals like water buffalo, which are a fraction of the size of elephants, are large enough as adults to be predated upon rarely (albeit more often than elephants).



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