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THAT HERBIVORY THREAD AGAIN
The 'carnivore descended from herbivore' thread has been shamelessly
resurrected, and Ronald Orenstein presents the following text.
> Among the marsupials the extinct Thylacoleo is probably a carnivore
> descended from a herbivore;
Thylacoleonids (Miocene-Pleistocene record, several genera now known) are dam
near certainly predatory, as scrape marks on their teeth show, but the
diprotodonts that gave rise to them may have been omnivorous from the start.
> Among the placentals the megalonychids were carnivores descended
> from 'creodont' herbivores (as are their descendants, the whales).
You mean mesonychids - megalonychids are ground sloths. And I hate to
be picky, but mesonychids and whales are 'condylarths' - they aren't
squat to do with the creodonts. Creodonts are the sister group to
carnivorans (together they form the Ferae), whereas 'condylarths' (a
name some mammalogists insist should be dropped forever) are part of
the Ungulata. Note also that some mesonychids were omnivorous or even
herbivorous (but others, like _Mesonyx_ itself, were nasty predators).
> I would be curious to know whether the sloths are considered to be
> descended from carnivorous xenarthrans or vice versa.
So would I. I'm pretty sure that herbivory is primitive for sloths, but further
back in xenarthran evolution I'm not so sure. I recall that _Ernanodon_, the
earliest xenarthran of which I'm aware (late Palaeocene of China), has been
interpreted as herbivorous: I believe that in the initial description (Ding
1979) it was compared with pandas. It shares features with both pilosans
(sloths) and vermilinguans (anteaters). The earliest known vermilinguan, the
early Eocene _Eurotamandua_, was already a specialized 'anteater'.
A recently published tome on the evolution of vermilinguans and cingulatans
('dillos) may sort all this out - I haven't seen it yet though. Sloths scream,
swim in the sea (probably), and they have too many neck vertebrae.
Note also that pangolins - which today are specialized eaters of ants and
termites - started out eating plants, and developed the clever technique of
exploiting leafcutter trails. It's thought that they ended up getting enough
energy from the ants to make it worthwhile eating them instead of the leaf bits
they were carrying.
Ahh, I guess that crash course I took in Palaeogene mammalogy is finally paying
off. So go on, flame me for not mentioning a single archosaur...
"You rebel scum!"
"Bounty hunters - we don't need that scum"