The family Apatemyidae has a long geochronological range in North
America, beginning in the Torrejonian land-mammal age, but is
represented by a relatively small number of fossils found at a few
localities. Two fossils of Orellan age, found in northeastern Colorado
and described here, demonstrate that the geochronological range of the
Apatemyidae extends into the Middle Oligocene. Isolated teeth of
_Sinclairella dakotensis_ Jepsen, part of a sample of a Chadronian
local fauna collected by field parties from the Webb School of
California, are also described.
I thank Mr. Raymond M. Alf, Webb School of California,
Claremont, California, and Dr. Peter Robinson, University of
Colorado Museum, Boulder, Colorado, for permitting me to
describe the fossils they discovered. Also Dr. Robinson made
available the draft of a short paper he had prepared on the
tooth found in Weld County, Colorado; his work was
facilitated by a grant from the University of Colorado
Council on Research and Creative Work. I also gratefully
acknowledge receipt of critical data and valuable comments
from Drs. Edwin C. Galbreath, Glenn L. Jepsen, and Malcolm
C. McKenna who is currently revising the Paleocene
apatemyids and studying the phylogenetic relationships of
the family. The prefixes of catalogue numbers used in the
text identify fossils in the collections of the following
institutions: KU, Museum of Natural History, The University
of Kansas, Lawrence; Princeton, Princeton Museum, Princeton,
New Jersey; RAM-UCR, Raymond Alf Museum, Webb School of
California, Claremont, California (the permanent repository
for these specimens will be the University of California,
Riverside); and UCM, University of Colorado Museum, Boulder,
Colorado. The system of notations for teeth prescribed for
use here is as follows: teeth in the upper half of the
dentition are designated by a capital letter and a number;
thus M2 is the notation for the upper second molar; teeth in
the lower half of the dentition are designated by a
lower-case letter and a number; thus p2 is the notation for
the lower second premolar.