Читать книгу Palæontological Report of the Princeton Scientific Expedition of 1877 - Francis Speir - Страница 4
MAMMALIA.
ОглавлениеPRIMATES.
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. T. No. 1. | M. T. No. 2. | M. T. No. 3. | |
| 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[1] | ·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 |
[1] 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.
