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Re: A Little Brain Teaser

In a message dated 95-10-24 11:22:59 EDT, theropod@garnet.berkeley.edu (John
R. Hutchinson) writes:

>Okay, here's a fun question for all of you to ponder: Name one carnivore
>(extant/extinct) that can be confidently said to be derived from an
>herbivorous ancestor. Omnivores don't count - this must be a bona fide
>carnivore (I'm not sure if insectivores count). Some graduate students here
>at Cal were talking about it yesterday and largely were stumped. All I
>could think up was that possibly carnivorous mid-Tertiary kangaroo
>(featured in Paleoworld once). I guess there's also that one
>desert-dwelling mouse that hunts voraciously (the one that howls). Any
>dinosaur examples that anyone can think of (I'm asking for good examples
>here, not wishy-washy possibilities)?

I've given this a little thought over the years, and I'm satisfied that
herbivory derived from strict carnivory is rare indeed. Since herbivory
requires some kind of specialized gastric flora to digest the cellulose, I
can see how it could derive much more easily from insectivory of plant-eating
insects: the bugs that digest plants inside the bugs remain in the digestive
tract of the insectivore, and eventually a symbiotic relationship develops.

So small, arboreal insectivorous archosaurs could evolve without too much
trouble into plant-eating dinosaurs. But we would have a lot more trouble
evolving a herbivorous therizinosaur from a carnivorous tetanuran...