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Re: cause of Gigantism in sauropods



Yes, elephant-lion is rare.

But Cape buffalo are a *major* part of lion diet, IIRC more than half of some 
lion populations' diet (Lake Manyara National Park is one, I think <60% Cape 
buffalo) and that's something like 3-4x the lion's mass; especially since 
lionesses do most of the hunting, and they're often like 120kg animals, not 
200kg. *Allosaurus amplexus* or *Saurophaganax* were larger in comparison to 
*Diplodocus carnegii*. 

And what were *Allosaurus amplexus* and *Saurophaganax* --doing-- if they 
weren't specialist sauropod, possibly big-sauropod, killers? Everything else 
*A. fragilis* was quite big enough to deal with.

But yes, the real titans were probably safe most of the time barring really 
hungry / desperate theropods. Still, the idea you sometimes see that 'adult 
sauropods were basically immune to predation' needs, at the least, 
qualification.

William Miller

----- Original Message -----
From: "Michael Habib" <MHabib@Chatham.edu>
To: vultur-10@neo.tamu.edu
Cc: "dinosaur" <dinosaur@usc.edu>
Sent: Monday, February 7, 2011 12:11:46 PM GMT -06:00 US/Canada Central
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).  

Cheers,

--Mike


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