He was apparently unaware of Clarence King's 1878 mention of Meniscotherium chamense in the fauna of his Vermilion Creek group in Wyoming. In a study of the knight faunas of southwestern Wyoming in 1952, I briefly summarized the history of the Meniscotherium discoveries and drew attention to their abundance.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 7
Some parts of the structure seem to indicate an affinity with Hyrax, but the limbs and feet show characters similar to those of primates, especially the extinct forms, and the like. Somewhat later that year (1892), Scott, although not certain that Meniscotherium was a direct ancestor of the modern hyracoids, was convinced by Marsh's (1892) depiction of the feet of "Hyracops".
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 9
GEOGRAPHIC AND GEOLOGIC OCCURRENCE
However, I agree with Van Houten and Simpson that, due to the vagaries of distribution, this does not justify a temporal correlation between Largo and Lost Cabin, as Granger (1915) hypothesized. There is no record of Meniscotherium in any of the early Eocene or Wasatchian horizons of the Big Horn Basin, after its occurrence in the latest Paleocene Clark Fork beds of the area.
NO. 2 A STUDY OF MENISCOTHERIUM GAZIN II at Tipton Butte, and an undetermined species is reported (Henry
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN I3
ENVIRONMENT
The I49 area, both above and below the Tipton tongue, as well as its beds, both above and below the Tipton tongue, as well as its beds in the Big Horn basin are barren for Meniscotherium. Nevertheless, coincident with the widespread extension of the Green River lacustral facies, the Tipton or Fontenelle tongue-Lake Gosiute intruding the marginal lowland Meniscotherium rohustum apparently became extinct.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN I5
In the Piceance Creek basin, only one of about 25 specimens from the Chicago Museum of Natural History has been definitely identified as Phenacodus. Discrepancies in the distribution of the smaller artiodactyls Diacodexis and Hexacodus also deserve discussion.
NO, 2 A STUDY OF MENISCOTHERIUM — GAZIN I9
20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 be little or no actual difference in foot structure among these —
CLASSIFICATION
Although there appear to be certain characters other than the size of the skull and postcranial skeleton which may be significant in distinguishing between the larger forms of M. The range in size there is much greater and is said to be continuous, so it does not no logical separation can be made between M.
THE SKELETON OF MENISCOTHERIUM, WITH NOTES ON PHENACODUS, HYOPSODUS, AND OTHER CONDYLARTHS
Now that the size variation is evident, I suspect that there is more than one species represented, not clearly definable in the material shown, or that there is a strong possibility for such a split.
SKULL
Lateral to this lip or ridge and medial to the prominent maxillary tuberosity is the posterior margin of the palatines. Its anterior margin appears to be roughly even with the posterior part or margin of the last molar.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 3I
32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 edly closer is the glenoid surface for the lower jaw articulation
I suspect that the aforementioned grooves on the ventrolateral surface of the petrosal may be for branches of a tympanic nerve plexus. The opening of the facial canal, however, is located slightly deeper anterodorsal to the fenestra ovalis; also hiatus Fallopii, quite large in one of the two speci-. The dorsomedial surface of the petrosal could not be seen in any of the Hyopsodus material without damaging the specimen.
ENDOCRANIAL CAST
The posterior margin is connected by an acre of the medial portion of the ventrally exposed mastoid, which also forms an anterior root of the paroccipital process. The medial margin of the petrosal in Hyopsodus shows a broad longitudinal groove formed in part by the lateral margin of the basioccipital. This groove clearly opens into the cranial cavity, medial to the anterior end of the petrosa, and undoubtedly carries the internal carotid artery, as interpreted.
36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49
NO, 2 A STUDY OF MENISCOTHERIUM — GAZIN 37 olfactory bulbs and their roots or peduncles, and particularly more
The cerebral hemispheres are quite widely separated along the midline, and the impression of the longitudinal or sagittal sinus made on the endocranium is clearly shown. It is interesting to note that at the confluence of the lateral sinuses with the sagittal sinus, the right branch invariably leaves the union at a somewhat lower level than the left. In Phenacodus, the cast does not include the shape of the sagittal and lateral venous sinuses above.
MANDIBLE
Posteriorly, as far as can be determined, its position also corresponds to the entry point for the internal carotid posteromedially and to the position of the foramenoval ventrolaterally where the third branch of the trigeminal would exit. A short distance anterodorsally from this, at the posteroventral edge of the surface formed by the petrosal, is a short slightly curved ridge that marks the cranial opening of the foramenlacerum posterius. The extended width and depth of the angle of the lower jaw indicate a large attachment area for the masseter muscle externally and the internal pterygoid muscle medially.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 4I
DENTITION
In the anterior part of the small median valley is the protoconule, isolated from the anterior cingulum and often from the deuterocone. The anterior cingulum usually extends around the base of the protocone and terminates in the valley between the protocone and the hypocone. In addition, there is a similar extension or ridge on the posterior wall of the entoconid (or hypoconulid?).
VERTEBRAE
Also, in addition to the posterior median ridge, which is the same as on the permanent tooth, rather pronounced ridges extend on the posterolingual and posterolateral slopes of the protoconid close to the thetalonid. In some Dp., the anterior extremity of this crest appears essentially double, almost as in. by Cope as 14 or 15.
48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 anterodorsally and laterally directed metapophysis is much larger
Cope believed that the number of sacral vertebrae was three, but his specimen may have been incomplete. Although slightly shorter, it is almost as large as the last sacral and has heavy, laterally directed transverse processes. Only the first four or five of the specimens shown show evidence of a neural spine, and the anterior caudals lack a clear ventral keel, but this is better defined posteriorly.
SCAPULA
Tail vertebrae. There are 14 caudal vertebrae (see Figure 9) belonging to one specimen, but most of these have not been found articulated, so that a sequential arrangement of these would probably be very incomplete.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 5I
HUMERUS
There is a generally shallow but well-defined fossa or depression, which may be pitted or nearly flat, on the posterior surface or margin of the greater tuberosity at the proximal end of the deltoid muscle, apparently the fossa for the teres minor that Cope mentioned as flat. The distal end of the humerus is broad with a very well developed inner condyle showing an entepicondylar foramen. With a posterior root extending into this posterior lateral crest of the trochlea and with an anterior root originating in the external condyle, the flared supinator crest extends prominently upward and slightly posteriorly over approximately the distal third of the shaft .
RADIUS
2 A STUDY OF MENISCOTHERIUM GAZIN Head, but showing a round, well-defined fossa for the teres minor. However, the medial facet of the scaphoid extends medially for a short distance over the anteroposterior crest of the styloid process. The radius in Phenacodiis resembles that of Meniscotherium in the character of the proximal articular surface of the humerus, but appears relatively slightly deeper anteroposteriorly.
ULNA
The distal end is enlarged and shows two almost circular, slightly concave facets next to each other, the lateral or lunal being slightly larger, anteroposteriorly. However, the shaft is relatively much sturdier, so the head does not appear as expanded.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 55
MANUS
Scaphoid. The scaphoid is relatively shortened proximodistally, but noticeably elongated in a dorsoventral direction and exhibits a knob-like ventromedial end. Furthermore, the convexity for articulation with the radius does not extend relatively as far down the dorsal surface as in Meniscotherium. The dorsal portion of the arcuate midsurface of the moon is faceted for articulation with the scaphoid.
NO, 2 A STUDY OF MENISCOTHERIUM — GAZIN 57 vex proximal articular surface for the radius, but this does not appear
The facet for the cuneiform is decidedly triangular and articulates well on the ventrolateral projection of the cuneiform. Trapezium.- The trapezium is broad and proximodistally deep in Meniscotherium, and its medial face is relatively flat. Trapezium.- The trapezium in Meniscotherium is markedly compressed proximodistally and almost wedge-shaped with the deepest portion at the dorsomedial corner of the bone.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 59 the second metacarpal is transversely convex but slightly concave
The distal articular surface for the proximal phalanx is similar to that of the second metacarpal, but more nearly symmetrical, and the transverse axis is. The proximal surface of the fourth metacarpal of Meniscotherium is more nearly triangular than that of the second metacarpal. The shaft of the fourth metacarpal is relatively straight and dorsoventrally flattened as in the others.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 63 of the articular surface has less diameter and its transverse axis is
64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 slightly toward the distal extremity, that of the third digit being
Unfortunately, the ramus of this bone and that of the ischium are poorly represented and poorly preserved in the material in question; however, enough remains to show the large, oval-shaped obturator foramen. The unnamed ion of Memscotherhun is remarkably like that of Phenacodus, although the latter is relatively more elongated and the crest of the ilium appears to be more flared and recurved. The base or posterior part of the ilium is slightly less triangular in cross-section with the pubic border on the ilium much more subdued than in Meniscotherium.
FEMUR
Furthermore, the head is almost spherical and the fossa for the ligmentum teres is centrally located, well removed from the border of the articular surface. It exhibits an elongated cnemial ridge that is laterally deflected and extends nearly half the length of the shaft. He further noted that the posterior face of the shaft distally is rough for muscular insertion.
FIBULA
The internal malleolus is abruptly truncated distally and the rounded anteromedial margin becomes more anterior in position proximally on the stem, in the direction of the clemial ridge. In addition, the distal ends of the metatarsals are relatively not as wide as in Phenacodiis primaevus. This process also deflects laterally the distoventral edge of the large, otherwise nearly vertical facet for the fibula.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 7I
Calcaneum.—The calcaneum of Meniscotherium is elongated with the posterior (proximal) projection comprising a little more than half the length. Anterolaterally, the condyle thickens and the rounded dorsal margin articulates with the distal margin of the external malleolus. This facet faces sharply ventrally on the posterior margin of the sustentaculum, as has been noted for the sustentacular facet of the astragalus.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 73
It is located just above the posterior end of the facet for the external wedge-shaped butine. Middle cuneiform.- The dorsoventrally elongate middle cuneiform is the smallest element of the Meniscotherium tarsus. Both the proximal and distal surfaces of the element are dorsoventrally concave, this for the navicular lake.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN ']']
More distally, the lateral surface matches the medial surface of the third metatarsal base, but I find no evidence of articular contact. In addition, there is a small flattened facet on the lateral surface for the ventral part of the fourth metatarsal base. Next to the curved ventral part of the cuboidal surface, on the medial side of the fourth metatarsal bone, is the facet of the third metatarsal bone.
The fifth metatarsal of Meniscotherium is a little longer than the first and about two-thirds the length of the fourth
Differences from Phenacodus and Tetraclaenodon fourth metatarsal are essentially those noted with regard to the second and third metatarsals, but it may be noted that the ventral part of the cuboid facet is not nearly so recurved, so that in these the base of fourth metatarsal does not extend as noticeably into peroneal groove. The phalanges of Phenacodus primaevus are relatively shorter and wider, and the distal phalanges are more widely spaced. Tetradaenodon phalanges are long and slender, not flattened, and the distal phalanx of each digit is.
SUMMARY OF RELATIONSHIPS
Convex and ventrally flat, and there is a small dorsal depression near the anterior margin, which is not itself notched. In general, the position of the hypocone is occupied by the metaconule in the early development of the selenodont pattern in the upper molars of artiodactyls (or by the protoconus in the cainotheres), but these both appear to be definable in Meniscotherium. However, the relative age of the Sao Jose de Itaborai, as well as that of the Casamayor community, seems to rule out the possibility that Meniscotherium could have given rise to these earlier proterotheriids, as would be implied in Wortman's postulation.
NO. 2 A STUDY OF MENISCOTHERIUM GAZIN 83 with the proterotheriid Anisolamhda which de Paula Couto (1952)
Russell (1964) gave a detailed description of the skull of Plenraspidotherium, and Pearson (1927), like Russell, presented the characters of the baseranium. According to Pearson (1927) the greater part of the paroccipital process is formed by the mastoid. A close relationship with Pleuraspidotherium has been postulated on the close similarity of the upper teeth.
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 93
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 95
EXPLANATION OF PLATES
NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 97
Cuboid from San Jose Formation, San Juan Basin, N. New Fork Member, Wasatch Formation. except cuboid from the San Juan Basin). Restoration of Meniscotherium by artist Walter Ferguson based on a composite skeleton from the San Juan Basin of New Mexico.
PLATES
