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George Olshevsky wrote:
>unless herbivory evolved twice in neighboring clades (Ornithischia and
>Sauropodomorpha), which is less parsimonious than assuming it evolved once.
It seems to me that the evolution of herbivores from carnivores
seems to be the rule, not the exception. Looking at dinosaurs, we have the
ornithischians, the sauropodomorphs, the ornithomimes, and the segnosaurs
as possible or probable herbivorous descendants of carnivores. We don't
have any serious proposals of a carnivorous group of dinosaurs descended
from herbivores, to my knowledge. The crocodiles, not known for fondness
of plants, also produced an herbivorous form.
I'm not too clear on mammalian evolution, but while I can cite one
herbivorous and a few omnivorous descendants of the carnivora (the panda,
bears, racoons) the closest you can get to carnivory in the perisso- and
artio- dactyls are the pigs.
Granted, these terms are not as exclusive as we make them out to
be- the hawiians raised dogs on vegetables for their meat, while we feed
our livestock ground-up livestock. And if the turtles are pareiasaurs,
then this would show that it does go the other way since many turtles,
after all, eat fish. But the general trend seems to be, among big
vertebrates at least, that carnivores produce herbivores but less often
is it the other way around.