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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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*** Start of this LibraryBlog Digital Book "Records of the Fossil Mammal Sinclairella, Family Apatemyidae, From the Chadronian and Orellan" ***
UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY
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
BY
WILLIAM A. CLEMENS, JR.
UNIVERSITY OF KANSAS
LAWRENCE
1964
UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
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
UNIVERSITY OF KANSAS
Lawrence, Kansas
PRINTED BY
HARRY (BUD) TIMBERLAKE, STATE PRINTER
TOPEKA, KANSAS
1964
29-8587
Records of the Fossil Mammal
Sinclairella, Family Apatemyidae,
From the Chadronian and Orellan
BY
WILLIAM A. CLEMENS, JR.
Introduction
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
dakotensis_.
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
dakotensis_.
Comments
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_.
TABLE 1.--MEASUREMENTS (IN MILLIMETERS) OF TEETH OF SINCLAIRELLA
DAKOTENSIS JEPSEN.
==========================================================================
| P4 | M1 | M2
-----------------------+------------+------------------+------------------
|length|width|length[1]|width[1]|length[1]|width[1]
-----------------------+------+-----+---------+--------+---------+--------
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
ALF, R.
1962. A new species of the rodent _Pipestoneomys_ from the
Oligocene of Nebraska. Breviora, Mus. Comp. Zool., no. 172,
pp. 1-7, 3 figs.
GALBREATH, E. C.
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.
JEPSEN, G. L.
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.
MCKENNA, M. C.
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.
MATTHEW, W. D.
1909. The Carnivora and Insectivora of the Bridger Basin, Middle
Eocene. Mem. Amer. Mus. Nat. Hist., 9:289-567, pls. 42-52,
118 figs.
PATTERSON, B. and MCGREW, P. O.
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.
SIMPSON, G. G.
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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