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Re: RÃ(c)p : Post–K-Pg Radiation of Placentals -- open



Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

>> The morphology-only trees all place Rodhocetus as a stem-cetacean.
>> (The parsimony-based trees are weird in putting Artiocetus closer to
>> the crown that Basilosaurus, though.) What's going on here?
>
> My suspicion: the molecular data are forcing the position of certain taxa,
> which are fixing the polarity/distribution of morphological traits in ways
> that morphology-only trees do not, which are pulling Rodho. out of its
> proper... er, its morphology-based position


Also, having the aquatic _Rodhocetus_ as a stem-euungulate implies
either that (1) both artiodactyls and perissodactyls evolved from an
aquatic ancestor; or (2) an aquatic lifestyle evolved independently in
_Rodhocetus_ and cetaceans.  Neither hypothesis seems especially
plausible.  Not to mention how it complicates the evolution of the
artiodactyl ankle.  The molecular data is undoubtedly the culprit in
shifting _Rodhocetus_ from its morphology-based position.






Cheers

Tim