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Re: Dilophosaurus Forelimb Bone Maladies



> On Mar 3, 2016, at 4:13 PM, Darius Nau <dariusnau@gmx.at> wrote:
> 
> Note that the _Cathetosaurus_ in question was probably nowhere close to 20t. 
> Jensen himself described it as a small sauropod no more than 10-15t in 
> weight, and that’s from a paper (and a time) full of sauropod mass estimates 
> that are excessive from a modern point of view (such as 80t _Brachiosaurus_).
> 
> Sadly Jensen really doesn’t seem to give any measurements of the material 
> that could be used to confirm its size (though there is an osteological 
> monograph that I don’t have access to which probably does…so if anyone has 
> better data on this, they’d be appreciated), but it’s a good guess that this 
> sauropod individual wasn’t much more than elephant-sized when it died.
> 
> Also the attacking theropod was implied to have been quite large, 
> _Torvosaurus_ or "fragmentary large allosaur"-size, so 3t is more like it.
> In the end I think the sauropod here is probably 2-3 times the size of its 
> purported attacker, not 10 times.

Fair enough - a twofold difference in size obviously evens the score quite a 
bit. Even then, though, predators that take animals twice their own mass are 
awfully rare in modern ecosystems, and Mesozoic ecosystems probably had 
proportionally more small prey (young dinosaurs) available than modern ones. So 
it still seems like a reach to consider this the norm (even if we accept 
Jensen’s reconstruction).


> Allosaurids seem equipped for both these scenarios, with dorsoventrally 
> strong but lightweight skulls and a cervical musculature and flexible neck 
> capable of both quick strikes and powerful head-depression to carve deeply 
> into flesh (Bakker 1998, Rayfield 2001, Snively et al. 2013).
> So I doubt think a would-be brontophage would have to rely on pure chance to 
> bring down a sauropod.

But the problem is not the ability to do damage so much as avoid receiving it. 
A lion has enough weaponry to kill a mature cape buffalo if it strikes in the 
just the right way. The reason that lions almost never do this appears to be 
that there is a very good chance that the buffalo does lethal damage in the 
process. The would-be brontophage can’t just be capable of dealing wounds - to 
be a regular predator of giant prey, it must have a reliable way of avoiding 
severe injury (reliable enough that the behavior can be used regularly with 
only a very small chance of mishap). The head and neck mechanics work you cited 
(especially the work by Eric Snively) applies just as well to a case where an 
allosaur bites something 500-800 kg in mass, for example. That’s still 
relatively large prey for a 2 ton animal. Certainly large enough for the 
head-depression carving to be useful. The capacity for rapid neck motions noted 
by Snively et al. also fits what we would predict to see from a sm
 all prey specialist.

Cheers,

—Mike H


Michael Habib, MS, PhD
Assistant Professor, Cell and Neurobiology
Keck School of Medicine of USC
University of Southern California
Bishop Research Building; Room 403
1333 San Pablo Street, Los Angeles 90089-9112

Research Associate, Dinosaur Institute
Natural History Museum of Los Angeles County
900 Exposition Blvd, Los Angeles, CA 90007

biologyinmotion@gmail.com
(443) 280-0181