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RE: No Cretaceous placental mammals?
> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu]On Behalf Of
> Guy Leahy
> If this interpretation is correct, perhaps the
> end-Cretaceous impact event had a more profound
> influence on mammal evolution than previously thought?
The paper in question is:
Wible, J.R., G.W. Rougier, M.J. Novacek & R.J. Asher. 2007. Cretaceous
eutherians and Laurasian origin for placental mammals near
the K/T boundary. Nature 447:1003-1006.
They find that no crown-group eutherian is known from the Cretaceous, and thus
the minimum divergence date is in the earliest
Cenozoic. (However, the authors admit that it might well be earlier).
The new eutherian phylogeny, produced with the inclusion of _Maelestes
gobiensis_ of the Djadokhta, and using a considerable spread
of Cretaceous eutherians and Paleogene mammals finds:
* monophyletic Euarchontaglires, Laurasiatheria, Xenarthra, and Afrotheria (the
latter two as sister taxa, and together the sister
taxon to laurasiatheres)
* the sister group to Placentalia is a clade comprised of _Purgatorius_,
_Protungulatum_, and _Oxyprimus_
* more distal outgroups are lepticids, zalambdalestids, _Deccanolestes_, a
Asioryctotheria + Cimolestida clade (the latter includes
_Maelestes_), an _Eozhelestes_ + _Paranyctoides_ clade, zhelestids,
_Montanaletes_, _Bobolestes_, and an (_Eomaia_ +
_Prokennalestes_)+ _Murtoilestes_ clade
* Eutherians that survived the K/Pg extinction include: _Cimolestes_,
lepticids, the _Purgatorius_ clade, and the placental
This parallels previous work on metatherian phylogeny, where crown group
metatheres (aka Marsupalia proper) are also restricted to
post-Cretaceous fossils, with a minimum divergence date in the earliest
Thomas R. Holtz, Jr.
Senior Lecturer, Vertebrate Paleontology
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
Building 237, Room 1117
College Park, MD 20742
Phone: 301-405-4084 Email: email@example.com
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796