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Re: Rép : Post–K-Pg Radiation of Placentals

Paula Gaubert <paulawilder@mac.com> wrote:

>  I read (what I could understand of) the pdf this morning; (am but a 
> fascinated, but innocent lay-person.)
> Is the New York Times article about the scientific findings presented this 
> morning quite okay ?
> http://www.nytimes.com/2013/02/08/science/common-ancestor-of-mammals-plucked-from-obscurity.html?hpw
> It seems to me that in an effort to present something that would attract the 
> great unwashed masses, the point of the scientific article has been
> re-centered, so that reads like an ode to the discovery of a new species of 
> shrew.  (I may be exaggerating slightly).

The article does seem to have conflated two separate (but not
necessarily mutually exclusive) concepts: (1) the earliest known
member of a group, and (2) the common ancestor of all members of a
group.  In this case, the group is the Placentalia (= crown placental
mammals).  _Protungulatum donnae_ (from the earliest Paleocene) is
regarded by the Science study as the oldest placental.  But this same
study did *not* find _Protungulatum donnae_ to be the common ancestor
of all placentals.  According to the presented phylogeny,
_Protungulatum donnae_ conmes out at the base of the Pan-Euungulata (=
extant hoofed mammals and their relatives, plus a bunch of fossil taxa
formerly called "condylarths").

(As an aside, if the very Late Cretaceous mammal _Protungulatum
coombsi_ belongs in the genus _Protungulatum_, then based on the
published phylogeny, this pushes back the origin of crown placentals
into the Mesozoic.  But the Supplementary Material is skeptical
regarding _coombsi_ being bona fide _Protungulatum_.)

_Protungulatum donnae_ is not actually "new"; it was named in 1965.
Tarsal bones referred to this critter indicate it was terrestrial (in
keeping with euungulate affinities).  The superficially shrew-like
"placental ancestor" depicted in the article was inferred by the
Science study to be scansorial (probably primitive for crown therians,
i.e. placentals + marsupials).  It's interesting to contemplate that
therians became scansorial and arboreal at about the same time (or
likely before) theropods are inferred to have headed into the trees.
Coincidence?  (There, finally made a mention of dinosaurs!)