TOMITHERIUM, Cope.
Ann. Rep. U. S. Geol. Survey of Terrs. 1872, p. 546.
"Dental formula of the inferior series: I. 2, C. 2, Pm. 4, M. 3.
The last molar has an expanded heel. The third premolar consists
of a cone with posterior heel. Fourth premolar exhibits, besides
its principal cone, an interior lateral one and a large heel. The
true molars support two anterior tubercles, of which the inner is
represented by two distinct cusps in one or more of them, and the
external is crescentoid in section. The posterior part of the crown
is wide and concave, and bordered at its posterior angles by an
obsolete tubercle on the inner, and an elevated angle on the outer
side." (Palæontology, Wheeler's Survey, iv (pt. 2), p. 135.)
Tomitherium rostratum, Cope.
Loc. cit., p. 548.
This species exhibits considerable variation, both in size and
proportion of the teeth. We have two specimens of it, one of which
agrees exactly with the measurements given by Professor Cope, while
the other is stouter, and probably belonged to an old male.
The incisors are too much broken for description. The canine has
a long, stout fang, which is subcircular in section; the crown
is compressed, and shows a distinct cutting edge posteriorly.
It is short, and tapers rapidly; in this respect differing from
_Notharctus_, Leidy, which has a long recurved canine. The first
and second premolars are inserted each by a single fang; the third
and fourth by two. The third premolar consists of a simple conical
crown with a small posterior heel; and the fourth has this heel
enlarged, with a small tubercle developed inside and slightly behind
the principal lobe. All the premolars have striated enamel, and very
feebly marked basal ridges.
The true molars are considerably larger than the premolars; the third
is the longest of the series, and the second is the widest. They all
seem to be inserted by two fangs. The posterior fang of the last
molar is a flat quadrate, of the same size throughout, having a great
fore-and-aft diameter, and apparently no nerve cavity. The mandible
is strong but shallow, has a curved alveolus and lower margin, and
the teeth form a curve with convexity outwards. The symphysis is
short and oblique.
This genus presents a close resemblance to the modern _Lemur_,
but at the same time shows several differences. We may give these
differences in systematic order: (1) Greater number of premolars, in
_Tomitherium_ = 4, in _Lemur_ = 2. It will be observed, however, that
the first and second premolars of _Tomitherium_ are very small and
single-rooted, and that their disappearance is a comparatively slight
change. (2) The canines are subcircular in section, not nearly so
much compressed. (3) Greater breadth of the molars in proportion to
their length. (4) Two internal cusps on the molar. (5) Much greater
size of the last molar. (6) Greater depth and thickness of the jaw.
(7) Greater curvature of alveolus and lower margin of ramus. (8)
Longer and more oblique symphysis.
The third and fourth premolars of _Tomitherium_ correspond almost
exactly to the first and second of _Lemur_, but they are not quite so
high and sharp. The interior tubercle of the second premolar is not
so distinct in the latter genus.
In the second specimen the cusps are all low, and the crests
prominent, giving the molars something of the appearance of
_Opisthotomus_. This difference is probably sexual.
_Measurements._
---------------------------------+---------+----------+--------
| M. | M. | M.
|T. No. 1.|T. No. 2. | Lemur.
---------------------------------+---------+----------+--------
Length of entire molar series | ·038 | ···· | ·032
Length of premolar series | ·017 | ···· | ·0125
Length of true molar series | ·021 | ···· | ·0195
Fore-and-aft diameter of canine | ·003 | ·005 | ·0065
Length of last molar[2] | ·008 | ···· | ·005
Width of last molar | ·004 | ···· | ·003
Length of second molar | ·007 | ·007 | ·0072
Width of second molar | ·005 | ·006 | ·005
Length of last premolar | ·0055 | ···· | ·007
Length of penultimate premolar | ·004 | ···· | ·005
Depth of jaw at second molar | ·012 | ·012 | ·0095
Thickness of jaw at second molar | ·0065 | ·009 | ·004
---------------------------------+---------+----------+--------
[Footnote 2: In measurements of teeth we use the word _length_ to
mean antero-posterior diameter, and _width_ to mean transverse
diameter.]
Specimen No. 1 was found at Cottonwood Creek, and specimen No, 2 at
Henry's Fork, Wyoming.
HYOPSODUS, Leidy.
Pr. Ac. Nat. Sc., 1870, p. 110.
Lower teeth: I. 3, C. 1, Pm. 4, M. 3, in uninterrupted succession.
Last molar has cusps in opposing pairs; the antero-internal cusp on
all the molars is single; the last molar has a heel, and the last
premolar has an inner cusp. The true molar cusps are all high and
simple.
Hyopsodus paulus, Leidy.
Loc. cit., p. 110.
This is one of the most common fossils found in the Bridger Basin.
We have numerous specimens, chiefly from Henry's Fork, exhibiting
a large range of individual and sexual variation. As Dr. Leidy has
already pointed out, the strength and depth of the lower jaw is
extremely variable, increasing with the age of the animal; so that
the most worn teeth are associated with the deepest jaws.
In addition to the jaws and teeth, (which have been very accurately
described), we have a portion of a pelvis and femur, which are
important as tending to confirm the reference of this genus to the
Lemurs.
The _pelvis_ is represented by the acetabulum and a small portion
of ilium and ischium. They resemble the corresponding parts in the
skeleton of _Stenops gracilis_. The acetabulum is a long oval, not
subcircular, deep, and quite narrow from side to side. It appears
to be directed nearly straight outwards. The ilium is narrow, has a
concave gluteal surface, and a prominent acetabular border. The pubis
evidently projected forward, making a right angle with the ilium;
while the ischium is slender and nearly in the same plane with the
ilium. The femur is thoroughly lemurine in shape. The shaft, (as
much of it as is preserved), is straight and sub-cylindrical; it is
not flattened even distally, but becomes very thick and trihedral
in shape just above the trochlea. The trochlea is long, and rises
obliquely upon the shaft; the groove is deep, and the two divisions
are asymmetrical, the external somewhat the larger. The condyles are
large. They are but slightly convex in either direction and project
backwards, and are broadest posteriorly. The internal is the larger.
They are separated by a deep but not wide popliteal groove, which
does not extend into a popliteal fossa. The position and shape of the
condyles are such as show that the femur must have been very oblique
to the tibia, as in the other lemurs. The tuberosities, especially
the internal, are very large and prominent. The whole distal end has
an asymmetrical appearance, owing to the greater size of the internal
condyle.
_Measurements._
M.
Breadth of ilium at acetabulum ·0065
Vertical diameter of acetabulum ·007
Transverse diameter of acetabulum ·009
Fore-and-aft diameter of shaft of femur above trochlea ·0065
Transverse diameter of shaft above trochlea ·0065
Width of trochlea ·004
Length of trochlea ·0075
Breadth over condyles ·010
Breadth of inner condyles ·005
OLIGOTOMUS, Cope.
Ann. Rep. U. S. Geol. Survey of the Terrs., 1872, p. 607.
"Molars constructed much as in _Hyopsodus_ and _Lophiotherium_, viz.,
with two external subtrihedral cusps which wear into crescents, the
posterior connected by a low oblique ridge with the basis of the
anterior cone of the inner side; the latter with two conic cusps. It
differs from these genera and from _Orotherium_ in the possession of
two premolars; the inferior molars are probably six, leaving four
true molars."
Oligotomus cinctus, Cope.
Loc. cit.
Represented in our collection by the penultimate lower molar, and a
caudal vertebra, which has a remarkably long, slender, and simple
centrum, with rudimentary metapophyses.
OPISTHOTOMUS, Cope.
Wheeler's Survey, Pal. v. iv., pt. 11, p. 152.
"The inferior lower molars do not display a bifid or double anterior
cusp; and the crowns exhibit two anterior cones, and an inner cone
and outer crescent posteriorly. The posterior crescent is well
defined, and is continued on a narrow crest to the anterior inner
tubercle. The posterior molar presents the peculiarity of a series of
three cusps in one line, the median having another or lateral cusp
near it."
This genus has hitherto been found only in the Wahsatch formation;
but we have discovered it to be represented in the Bridger series by
the species _O. astutus_, Cope. Our specimen consists of a part of
the ramus mandibuli containing a single molar tooth.