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Re: Dilophosaurus Forelimb Bone Maladies

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.

It’s a common strategy among animals that kill large prey, at least those with a sharp, polyphyodont dentition, to disable some part of the locomotive system. Great white sharks bite the caudal peduncle when they take sizeable cetaceans (Long & Jones 1996), and they reportedly employ a similar methods against elephant seals. Komodo dragons sever the leg tendons of everything from deer to water buffalo and then finish it off (there is ample camera footage of this, but it also contains ample amounts of deer getting their intestines torn out while still alive, so consider yourselves warned).

In this case though, the bite marks are on the pelvis. The hindlimbs weren’t found though, so that doesn’t necessarily preclude a hamstringing-style attack.

But given that Jensen’s hypothesis is correct (and I’m not saying it must be, but I do not disagree with his premise that a large Jurassic theropod could have successfully attacked and killed the sauropod in question), there’s another possibility, which is a deep bite to the pelvic musculature, both providing immediate nutrition in a possible 'flesh-grazing' scenario (equivalent to raptorial delphinids or accipitrids), and causing significant functional impairment and exsanguination.

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.

Bakker, Robert T. (1998): Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues. Gaia, 15 pp. 145-158. Long, Douglas J.; Jones, Robert E. (1996): White Shark Predation and Scavenging on Cetaceans in the Eastern North Pacific Ocean. In: Klimley, Peter A.; Ainley, David G.: Great White Sharks: the biology of Carcharodon carcharias. San Diego, pp. 293-307. Rayfield, Emily J.; Norman, David B.; Horner, Celeste C.; Horner, John R.; Smith, Paula M.; Thomason, Jeffrey J.; Upchurch, Paul (2001): Cranial design and function in a large theropod dinosaur. Nature, 409 (6823) pp. 1033-1037. Snively, Eric; Cotton, John R.; Ridgely, Ryan; Witmer, Lawrence M. (2013): Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda). Palaeontologia Electronica, 16 (2) pp. 1-29.

On 03.03.2016 23:39, Dann Pigdon wrote:
On Fri, Mar 4th, 2016 at 5:56 AM, Mike Habib <biologyinmotion@gmail.com> wrote:

A two ton predator would have to be suicidal to take on a 20 ton animal.

That depends on what you mean by 'take on'. A direct assault on a healthy 
animal is unlikely to
succeed, but a loud and ferocious bluff might be enough to panic a sauropod 
into stumbling and
injuring itself, turning it's own mass against it.

A sauropod with a severely injured leg is unlikely to survive for long, 
especially if it's left lying on its
side and unable to right itself, leading to the sort of complications that 
large beached whales fall prey
to (breathing difficulties, internal injuries). Even a sauropod with a slight 
limp may be doomed if it
can't forage effectively enough. It would require a very patient predator to 
follow it around until it was
too weak to effectively fight back though.

I often wonder whether sauropods ever dared to drink water directly from rivers 
or waterbodies, given
the size of some of the crocodilians about during the Mesozoic. A drinking 
sauropod would seem to
present an easily killed target if it presented its head in a convenient 
position to be swiftly
decapitated. Perhaps there's a reason why we find so many headless sauropod 
fossils. :-)

Yours sincerely,

Darius Nau