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Re: Morpho v molecular (was Re: Tinamous: living dinosaurs)
But what you're actually talking about isn't the position of the whales
anymore. It's the position of the ruminants -- as I first said on this list
a couple of years ago.
In the context of Whippomorpha, this is a distinction without a
difference, surely? Although strictly speaking the clade Whippomorpha
is the hippopotamid-cetacean clade (preferably known as Cetancodonta),
it's the proposed position of the the whippomorphs/cetancodonts as
sister taxon to the Ruminantia that's far more contentious, and is
inextricably linked with the molecular-based phylogeny.
That's what I'm saying: the position of Ruminantia is more contentious
now than the position of Cetacea.
Morphology traditionally puts the ruminants next to the camels (together
Selenodontia), molecules put them next to the whippomorphs.
I think it's worth mentioning that camelids (modern tylopods) are
actually ruminants, in an ecomorphological sense. They just don't
belong to the clade Ruminantia. The selenodont dentition and complex
digestive processes are actually linked. Having a basal Tylopoda and
a derived Ruminantia requires that "chewing the cud" evolved twice (by
Tylopoda and Ruminantia) - or was lost twice (by Suina and
Cetancodonta). The purpose of my excursion into neontology is that
these molecular-based often phylogenies involve complicated
side-effects in terms of explaining certain anatomical and behavioral
traits of modern mammals.
The tragulids, the extant sister-group to all other extant ruminants,
have incomplete rumination in that the third chamber of the stomach is
poorly developped. At least part of the system does seem to have evolved