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FISH-EATING THEROPODS



Dr Paul M.A. Willis wrote:

> But when I heard that they found fish scales in the
> stomach region of Baryonyx, I was convinced that it probably was a
> piscivore.

and Nick Longrich wrote:

> Exclusive piscivores, probably not, animals in general have a
> broader diet than we usually give them credit for. But heavily, even
> primarily, piscivorous? That seems very possible. Certainly they did not
> hunt in a manner like Allosaurus or Tyrannosaurus, whatever they hunted.
>    By the way, what kind of depositional environment were these
> things found in?

My problem is not that _Baryonyx_ et al ate fish, or even ate a lot of
fish, it's with the term "piscivore." The implication (to me, at least, and
I think, unfortunately, to the general populace) of the term piscivore is
that the animal ate fish *exclusively*, not just some or most of the time.
As stated previously, 70% of the diet of modern crocodilians is fish. Yet
larger species take large mammals as well, and all crocs are opportunistic
feeders, dining upon whatever prey (of whatever size) they happen upon.
With this varied diet, are they considered piscivores because *most* of
what they eat is fish? It seems to me that this is simply standard
predacious behavior. Crocs (to which _Baryonyx_ has been compared) eat a
lot of fish because they are primarily aquatic animals. Theropods, however,
are terrestrial animals, and it would only seem logical that even if they
ate fish on a regular basis, they would still take other prey. Regarding
Tracy Ford's comment about _Iguanodon_: it is a presumption that large
predators only hunt large prey; extant predators take small prey as often
as large, and I'm sure that there was plenty of small prey
(_Hypsilophodon_, _Valdosaurus_, juveniles of larger species) for
_Baryonyx_ to eat as well.

Large crocodilians have no problem biting into and tearing out chunks of
meat from large mammalian prey. How is _Baryonyx_ any different? _Baryonyx_
teeth, to my knowledge, while semi-conical in cross-section, are finely
serrated, a typical theropod trait. Does anyone out there know if
crocodilian teeth are similarly serrated? If so, then what works for crocs
would work for _Baryonyx_. And if not, then it seems to me that _Baryonyx_
had an advantage when biting into larger prey.

And the depositional environment of a fossil is not necessarily indicative
of where it lived, only where it died. An animal that died in the middle of
the woods is much less likely to be quickly buried and preserved than an
animal that died near a river or lake that could flood and cover the body.

Brian Franczak (franczak@ntplx.net)