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IRRITATOR THE PISCIVOROUS



On 10/28/96, Darren Naish says:

> Dino-artist Steve White has suggested (basing his logic on the idea
> that _Irritator_ was a piscivore) that the animal may have had big
> intermeshing teeth like, say, the pterosaur _Caeradactylus_, but
> this is also merely speculative.

Where did Steve White get the idea that _Irritator_ was a piscivore? Is it
because _Irritator_ is considered a possible relative to _Baryonyx_,
sharing as it does  some characteristics with that animal (this is the idea
reflected in Salas' illustration in PT)? Since _Irritator_ is known only
from an incomplete skull and no post-cranial material, that assertion is
questionable, but possible. If this association is indeed the root of his
perception of its piscivorous nature, the idea stems from the
much-publicized description of _Baryonyx_ as a piscivore, since it was
discovered with the remains of partly digested fish scales inside its
ribcage; its semi-conical teeth and elongate crocodile-like snout added to
the idea.

Piscivorous means "fish-eating." The question then becomes, why is
_Baryonyx_ considered a piscivore? Because it appears crocodilian in some
aspects, and because a single specimen of _Baryonyx_ ate a single fish?
This is not a logical assumption. Since it's being compared to a
crocodilian, let's take a look at the eating habits of living crocs. First,
no extant crocodilian, including the gharial, is *exclusively* a
fish-eater. While fish may make up 70% of the bulk in the diet of most
species, all crocodilians supplement their diet; the biggest species tend
to take larger prey that includes more mammals. Secondly, and most
importantly, please remember that crocodilians are primarily aquatic, not
terrestrial, animals. Fish, therefore, are the most numerous prey in their
environment. In every habitat, crocodilians will eat whatever prey is
available; even crocs larger than 15 feet include such animals as snails,
crabs, frogs, and small fish in their diet.

In recent years, descriptions of dinosaur behavior have become increasingly
specious. _Baryonyx_ has been (and is still being) portrayed as swatting
fish out of the water with its over-sized claw, rather like a grizzly bear
in pursuit of salmon, despite the fact that its crocodile-like teeth and
snout are better-suited to the task of snatching fish from the water and
the paddle-shaped paw of a bear and the three-fingered theropod manus are
not analogous structures. Steve White at least has _Irritator_ hunting fish
with its head, but his idea that it had intermeshing teeth a la
_Cearadactylus_ is not "merely speculative," it is totally unfounded, since
no known theropod (including the presumably-related _Baryonyx_, for which
the premaxilla is known) had such teeth. Obviously, _Baryonyx_ ate fish (at
least one did, once). Actually, I do not doubt that it even actively hunted
them, since its head does seem suited to the task. But to call it (and
through association, all its relatives) piscivorous when it was more likely
simply an opportunistic omnivore, is both imprecise and misleading.