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Title: Records of the Fossil Mammal Sinclairella, Family Apatemyidae, From the Chadronian and Orellan
Author: Clemens, William Alvin
Language: English
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Volume 14, No. 17, pp. 483-491, 2 figs.
March 2, 1964

Records of the Fossil Mammal
Sinclairella, Family Apatemyidae,
From the Chadronian and Orellan





Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
Theodore H. Eaton, Jr.

Volume 14, No. 17, pp. 483-491, 2 figs.
Published March 2, 1964

Lawrence, Kansas




Records of the Fossil Mammal
Sinclairella, Family Apatemyidae,
From the Chadronian and Orellan




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.

Family APATEMYIDAE Matthew, 1909

Genus =Sinclairella= Jepsen, 1934

=Sinclairella dakotensis= Jepsen, 1934

The type of the species, Princeton no. 13585, was discovered in
Chadronian strata of the upper part of the Chadron Formation cropping
out in Big Corral Draw, approximately 13 miles south-southwest of
Scenic, in southwestern South Dakota (Jepsen, 1934, p. 291). Detailed
descriptions of the type specimen are given in papers by Jepsen (1934)
and Scott and Jepsen (1936). Isolated teeth of Chadronian age referable
to _Sinclairella dakotensis_ have been discovered subsequently at a
locality in Nebraska and fossils of Orellan age, also referable to _S.
dakotensis_, have been collected at two localities in Colorado. The
sample from each locality is described separately.

Sioux County, northwestern Nebraska

     _Material._--RAM-UCR nos. 381, left M1; 598, left m2; 1000,
     right m1; 1001, right m2; 1079, right m2; 1674, right M2;
     and 3013, left m2.

     _Locality and stratigraphy._--These Chadronian fossils were
     discovered by Raymond Alf and members of his field parties
     in several harvester ant mounds built in exposures of the
     Chadron Formation in Sec. 26, T 33 N, R 53 W, Sioux County,
     Nebraska (Alf, 1962, and Hough and Alf, 1958). This is UCR
     locality V5403. The collectors carefully considered the
     possibility that some of the fossils found in the ant mounds
     were collected from younger strata by the harvester ants and
     concluded this was unlikely (Alf, personal communication).

     _Description and comments._--The cusps of RAM-UCR no. 381, a
     left M1, are sharp and the wear-facets resulting from
     occlusion with the lower dentition are small. The paraconule
     is a low, ill-defined cusp on the anterior margin of the
     crown; a metaconule is not present. A smooth stylar shelf is
     present labial to the metacone. The crown was supported by
     three roots. There are no interradicular crests.

     The crown of RAM-UCR no. 1674, a right M2, is heavily
     abraded and many morphological details of the cusps have
     been destroyed. Low interradicular crests linked the three
     roots of the tooth with a low, central prominence. As was
     the case with RAM-UCR no. 381, no significant differences
     could be found in comparisons with illustrations of the
     teeth preserved in Princeton no. 13585.

     RAM-UCR nos. 598, 1001, 1079, and 3013 all appear to be
     m2's. The talonids of these teeth are not elongated, their
     trigonids have quadrilateral outlines, and the paraconids
     are small but prominent, bladelike cusps. The trigonid of
     RAM-UCR 1000 is elongated and the paraconid is a minute
     cusp; the tooth closely resembles the m1 of the type of
     _Sinclairella dakotensis_.

Logan County, northeastern Colorado

     _Material._--KU no. 11210 (fig. 1), a fragment of a left
     maxillary containing P4 and M1-2.

     _Locality and stratigraphy._--The fossil was found in the
     center of the W-1/2, Sec. 21, T 11 N, R 53 W, Logan County,
     Colorado, "... in the bed below _Agnotocastor_ bed, Cedar
     Creek Member...." (Ronald H. Pine, 1958, field notes on file
     at the University of Kansas). The bed so defined is part of
     unit 3 in the lower division of the Cedar Creek Member, as
     subdivided by Galbreath (1953:25) in stratigraphic section
     XII. The fauna obtained from unit 3 is of Orellan age.

[Illustration: FIG. 1. _Sinclairella dakotensis_ Jepsen, KU no. 11210,
fragment of left maxillary with P4 and M1-2; Orellan, Logan County,
Colorado; drawings by Mrs. Judith Hood: a, labial view; b, occlusal
view; both approximately × 9.]

     _Description and comments._--P4 of KU no. 11210 has a large
     posterolingual cusp separated from the main cusp by a
     distinct groove, which deepens posteriorly. The
     posterolingual cusp is supported by the broad posterior
     root. P4 of the type specimen of _Sinclairella dakotensis_
     is described (Jepsen, 1934, p. 392) as having an oval
     outline at the base of the crown, and a small,
     posterolingual cusp. A chip of enamel is missing from the
     posterior slope of the main cusp of the P4 of KU no. 11210.
     The anterior slope of the main cusp is flattened, possibly
     the result of wear, and there is no evidence of a groove
     like that present on the P4 of the type specimen.

     Only a few differences were found between the molars
     preserved in KU no. 11210 and their counterparts in the type
     specimen. A stylar shelf is present labial to the metacone
     of M1 of KU no. 11210, but, unlike the type, its surface is
     smooth and there is no evidence of cusps. Of the three small
     stylar cusps on the stylar shelf of M2 the smallest is in
     the position of a mesostyle. The M2 lacks a chip of enamel
     from the lingual surface of the hypocone. Unlike the M2 of
     Princeton no. 13585, in occlusal view the posterior margin
     of the M2 of KU no. 11210 is convex posterior to the
     metacone. The anterior edge of the base of the zygomatic
     arch of KU no. 11210 was dorsal to M2. The shallow oval
     depression in the maxillary dorsal to M1 might be the result
     of post-mortem distortion.

     The molars preserved in KU no. 11210 and their counterparts
     in the type specimen do not appear to be significantly
     different in size (table 1) or morphology of the cusps. The
     only difference between the two specimens that might be of
     classificatory significance is the difference in size of the
     posterolingual cusp of P4. At present the range of
     intraspecific variation in the morphology of P4 has not been
     documented for any species of apatemyid. The evolutionary
     trend or trends of the apatemyids (McKenna, 1960, p. 48) for
     progressive reduction of function of p4 probably were
     paralleled by similar trends in the evolution of the P4. If
     so, the intraspecific variation in the morphology of P4
     could be expected to be somewhat greater than that of the
     upper molars, for example. The morphological difference
     between the P4's of the type of _Sinclairella dakotensis_
     and KU no. 11210 is not extreme and does not exceed the
     range of intraspecific variation that could be expected for
     this element of the dentition. The close resemblances in
     size and morphology between the M1-2 of Princeton no. 13585
     and KU no. 11210 also favor identification of the latter as
     part of a member of an Orellan population of _Sinclairella

Weld County, northeastern Colorado

[Illustration: FIG. 2. _Sinclairella dakotensis_ Jepsen, UCM no. 21073,
right M2; Orellan, Weld County, Colorado; drawing by Mrs. Judith Hood:
occlusal view, approximately × 9.]

     _Material._--UCM no. 20173 (fig. 2), is a right M2.

     _Locality and stratigraphy._--The tooth was discovered at
     the Mellinger locality, Sec. 17, T 11 N, R 65 W, Weld
     County, Colorado. The Mellinger locality is in the Cedar
     Creek Member, White River Formation, and its fauna is
     considered to be of Orellan age (Patterson and McGrew, 1937,
     and Galbreath, 1953).

     _Description and comments._--UCM no. 21073, which is more
     heavily abraded than KU no. 11210, shows no evidence of a
     stylar cusp either anterolabial to the metacone or in the
     position of a mesostyle. A small stylar cusp is present
     anterolabial to the paracone. A notch that appears to have
     been cut through the enamel of the posterolabial corner of
     the crown could have received the parastylar apex of M3. A
     similar notch is not present on the M2 of KU no. 11210 nor
     indicated in the illustrations of the M2 of Princeton no.
     13585. The coronal dimensions of UCM no. 21073 (table 1) do
     not appear to differ significantly from those of the M2's of
     KU no. 11210 and the type specimen of _Sinclairella


With the discovery of Orellan apatemyids the geochronological range of
the family in North America is shown to extend from the Torrejonian
through the Orellan land-mammal ages. The discoveries reported here
enlarge the Oligocene record of apatemyids to include not only the type
specimen of _Sinclairella dakotensis_, a skull and associated mandible
from South Dakota, but also seven isolated teeth, representing at least
two individuals, from a Chadronian fossil locality in Nebraska and one
specimen from each of two Orellan fossil localities in northeastern
Colorado. Simpson (1944:73, and 1953:127) presented tabulations of the
published records of American apatemyids and suggested the data
indicated the populations of these mammals were of small size
throughout the history of the family. The few pre-Oligocene occurrences
of apatemyids described subsequently (note McKenna, 1960, figs. 3-10,
and p. 48) and occurrences described here tend to reinforce Simpson's
interpretation. This interpretation may have to be modified to some
degree, however, when current studies of collections of pre-Oligocene
apatemyids are completed (McKenna, personal communication).

Although information concerning the evolutionary trends of American
apatemyids has been published, no data on the morphological variation
in a population are available in the literature. An adequate basis for
evaluating the significance of the morphological differences between
the P4's of Princeton no. 13585 and KU no. 12110 coupled with the
similarities of their M1-2's is lacking. In the evolution of American
apatemyids the P4 underwent reduction in size and, apparently,
curtailment of function. This history suggests the range of
morphological variation of P4 in populations of _Sinclairella
dakotensis_ could be expected to be greater than that of the molars and
encompass the morphological differences between the P4's of Princeton
no. 13585 and KU no. 12110. The difference in age of the Chadronian and
Orellan fossils does not constitute proof that they pertain to
different species. Although the identification is admittedly
provisional until more fossils including other parts of the skeleton
are discovered, the Orellan fossils described here are referred to
_Sinclairella dakotensis_.


                       |     P4     |        M1        |        M2
Princeton no. 13585[2] | 2.1  | 1.1 |   4.0   |  3.7   |   3.4   |  4.7
RAM no. 381            |      |     |   4.1   |  3.5   |         |
RAM no. 1674           |      |     |         |        |   3.4   |  4.2
KU no. 11210           | 2.4  | 1.6 |   3.9   |  3.5   |   3.8   |  4.1+
UCM no. 21073          |      |     |         |        |   3.6   |  4.1
                                    |       m1         |        m2
                                    |  length |  width |  length | width
Princeton no. 13585[3]              |    3.5  |   2.4  |    3.7  |  2.8
RAM no. 1000                        |    3.5  |   2.2  |         |
RAM no. 598                         |         |        |    3.8  |  2.6
RAM no. 1001                        |         |        |    3.6+ |  2.6
RAM no. 1079                        |         |        |    4.0  |  2.8
RAM no. 3013                        |         |        |    3.6  |  2.8

[Footnote 1: Length defined as maximum dimension of the labial half of
the crown measured parallel to a line drawn through the apices of
paracone and metacone. Width defined as maximum coronal dimension
measured along line perpendicular to line defined by apices of paracone
and metacone.]

[Footnote 2: Dimensions provided by Dr. Glenn L. Jepsen.]

[Footnote 3: Dimensions taken from Jepsen (1934:300).]

Literature Cited

    1962. A new species of the rodent _Pipestoneomys_ from the
          Oligocene of Nebraska. Breviora, Mus. Comp. Zool., no. 172,
          pp. 1-7, 3 figs.

    1953. A contribution to the Tertiary geology and paleontology
          of northeastern Colorado. Univ. Kansas Paleont. Cont.,
          Vertebrata, art. 4, pp. 1-120, 2 pls., 26 figs.

HOUGH, J., and ALF, R.
    1958. A Chadron mammalian fauna from Nebraska. Journ. Paleon.
          30:132-140, 4 figs.

    1934. A revision of the American Apatemyidae and the description
          of a new genus, _Sinclairella_, from the White River
          Oligocene of South Dakota. Proc. Amer. Philos. Soc.,
          74:287-305, 3 pls., 4 figs.

    1960. Fossil Mammalia from the early Wasatchian Four Mile fauna,
          Eocene of northwest Colorado. Univ. California Publ. in
          Geol. Sci., 37:1-130, 64 figs.

    1909. The Carnivora and Insectivora of the Bridger Basin, Middle
          Eocene. Mem. Amer. Mus. Nat. Hist., 9:289-567, pls. 42-52,
          118 figs.

    1937. A soricid and two erinaceids from the White River Oligocene.
          Geol. Ser., Field Mus. Nat. Hist., 6:245-272, figs. 60-74.

SCOTT, W. B. and JEPSEN, G. L.
    1936. The mammalian fauna of the White River Oligocene--Part I.
          Insectivora and Carnivora. Trans. Amer. Philos. Soc., n. s.,
          28:1-153, 22 pls., 7 figs.

    1944. Tempo and mode in evolution. New York: Columbia Univ. Press,
          xviii + 237 pp., 36 figs.

    1953. The major features of evolution. New York: Columbia Univ.
          Press, xx + 434 pp., 52 figs.

_Transmitted June 24, 1963._

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