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mammal radiation ONLY after dinosaur extinction



In the hopes of throwing an (IMHO) necessary bucket of cold water on
John Bois' egg idea, I'd like to quote from the article that
ostensibly caused John to revive the discussion:

  Near the Cretaceous-Tertiary boundary (65 Ma), archaic ungulates
  appear in North America and shortly thereafter in South America
  (ref), thus beginning a tremendous taxonomic and ecological radiation
  leading to the present ungulate diversity that ranges from antelope
  to elephants to whales.

The fact that proto-ungulates apparently arose 20 million years before
the non-avian dinosaurs died out is significant only because their
descendents later radiated into so many contemporary mammal species.
The new finds and newly proposed phylogenetic significance of older
finds are interesting for a lot of reasons, but they do NOT throw into
question the currently accepted scenario for mammalian evolution --
that the adaptive radiation that ultimately lead to contemporary
mammalian diversity was possible only AFTER the ecological release
brought about by the demise of the dinosaurs.  Archibald isn't
claiming to have found that cows lived with the dinosaurs.  He's
saying that some of the little ratty things that did live with the
dinosaurs had teeth that show that these particular little ratty
things were probably part of the lineage that eventually gave rise to
cows (i.e. ungulates).  (In case you wonder why I somewhat
pejoratively refer to the animals as "little ratty things", please
note that their largest molars were only about 2 mm (less than 1/10th
of an inch) from back to front).

Source of quote:

Archibald, J. D. (1996). "Fossil Evidence for a Late Cretaceous Origin
of "Hoofed" Mammals", _Science_, 272:1150-1153.

(the quote appears on page 1152).

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)