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Re: FISH-EATING THEROPODS



Brian Franczak wrote:

>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.

Certainly within crocs, longirostrine species are considered to be
piscivores even though most will take birds, small mammals or whatever else
comes its way. However the majority of their diet is fish. Significantly,
dietary analysis of even very large, broad-snouted crocs indicates that the
bulk of their diet is often insects and small crustaceans.

>Large crocodilians have no problem biting into and tearing out chunks of
>meat from large mammalian prey.

Not strictly true. While large broad-snouted (platyrostral) crocs can take
big bites, they don't tear chunks of food because their teeth are not
acpable of doing this. Usually they simply latch on until the prey dies
from suffocation, loss of blood, drowning, shock or a combination of these.
Dismembering of prey is by rolling while maintaining a strong grip on the
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.

Among modern crocs I have heard of a single specimen of Crocodylus porosus
with serrate carinae. Among fossil crocs, the only one I am aware of with
conical teeth and serrate carinae is Pallimnarchus pollens. This was an
extreme platyrostral species that probably specialised in attacks from very
shallow water.

>And the depositional environment of a fossil is not necessarily indicative
>of where it lived, only where it died.

Or rather, where the carcass came to rest.

>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.

Correct. I don't think that we are any closer to understanding the full
dietary range of Baryonyx and pursuing the analogy of some similarities
with some crocs will only be of limited use. However, the finding of fish
scales in the stomach of Baryonyx indicates that it did eat fish. How far
one can reconstruct the full diet of a species of animal based on a single
incomplete fossil specimen is suspect. Speculating beyond the evidence is
the stuff of fairies.

Cheers, Paul

Dr Paul M.A. Willis
Consulting Vertebrate Palaeontologist
Quinkana Pty Ltd
pwillis@ozemail.com.au