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Re: What did Spinosaurus eat? New species of Lepidotes found



2011/3/1 Jaime Headden <qi_leong@hotmail.com>:
> Haro and Williams when they are right and say things better than I do).
>
Being sincere, the former text by me looks like very badly expressed
and mixed-up after I posted it, on the part on spinosaurs at least, so
I would not say I say things better than anyone...

>   Most carnivores should have no difficulty processing the carcass of such an 
> animal as a croc at 4 m, close to its own size perhaps. This likely happened 
> for a lot of biotas from the Chinle to the Hell Creek. What is speculated 
> seems to be the potential to _hunt_ crocodiles,

Yes, sorry, I was trying to say hunt crocodiles, and that the
crocodiles form a large share of the diet, so that the predator could
not live if there were no crocodiles around.

Even when at times a pride of lions can kill even large crocodiles (a
case is mentioned by Schaller, 1972, in "The Serengeti Lion"), and
even if they were fast enough to avoid the crocodilian defenses, I do
not think the small global biomass of sympatric slow-growing
crocodiles may sustain by itself a population of large carnivorous
mammals as lions.

> and in that, our minds turn to spinosaurs plunging into rivers and lakes and 
> surfing to find those delectable *Stomatosuchus* and *Sarcosuchus* and 
> *Bernissartia*.

I think the theropod would have to be larger than the croc in order to
safely prey upon it. Most Mesozoic crocodiles did not have the size of
Sarcosuchus or Stomatosuchus and may be good prey. The armor of these
two crocs, together with their size may keep them safe from
Spinosaurus, which does not seem to have a very powerful bite. Nor
would I say Sarcosuchus and Stomatosuchus were great menace for
Spinosaurus, because Stomatosuchus lacks large enough teeth, and
Sarcosuchus mostly resembles a gharial, and would for the most have
hunted large fishes: the relatively greater robustness of the jaws of
Sarcosuchus when compared to the modern gharial may simply account for
scaling, and the fact that isometry would yield a proportionally
weaker animal. These jaws, however, are by far behind the robustness
present in Alligator and the larger modern Crocodylus species known to
actively hunt proportionally large prey, at a size much smaller (I
think Sarcosuchus may have been at risk of breaking its jaws if
attempting to tackle a dinosaur near its size, a person with greater
mechanical knowledge may have the last word on this). And I do not
know of gharials being a menace for mammals near its size or even
slightly smaller (though Sarcosuchus bears a downwards-curved teeth
which may have helped it tearing flesh out of large corpses better
than a gharial).
>
>   But in the era of tyrannosaurs and spinosaurs, there are more than aquatic 
> crocs, and in this case, terrestrial forms both large and small were 
> prevalent.
>
True, I was interested in those on the water, mostly regarding the
presumed amphibious habits of Majungasaurus. It seems that crocodile
diversity was far larger in the Cretaceous than today, thus suggesting
also a proportionally larger crocodilian total biomass in their
ecosystems, and thus a good resource. Now, I am not sure if most
Cretaceous crocodyliforms were very far from the water...

> Maybe those large crocs filled the niche of croc-hunting.  It doesn't have to 
> be a theropod.

Or both if the small crocodiles were common...