Monoclonius dawsoni Lambe 1902
Creators: name: Lambe L., M.
Publisher: name: Zenodo
Year: 1902
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Dinosauria
Ceratopsidae
Monoclonius
Monoclonius dawsoni

description: Monoclonius dawsoni. Sp. nov. Plate XVI, plate XIX, &amp;filig;gs. 4 - 6, and plate XX, &amp;filig;gs. 3 and 4. The* remains of an apparently undescribed species of this genus, consisting of the skull of one individual and the posterior crest of another, are of especial interest. The skull when found lay on its right side and although very much crushed, certain parts of it supply de&amp;filig;nite information as to its structure and size. The two orbits. the right maxilla, a quadrate and the occipital condyle were conspicuous and apparently in place, with a large posterior crest extending to the rear. Somewhat in advance of the orbits a horn core, of large size and apparently symmetrical form, occupied a position suggestive of a nasal origin. the nasal bones and the frontals being probably represented by the ragments &amp;filig;lling the space between the orbit and the horn core (see &amp;filig;g. 14, from a measured drawing made before the parts of the skull were removed). ) The large posterior crest forms the back part of the skull above; its exact shape is fortunately supplied by the admirably preserved specimen shown in outline. from beneath, in iig. 15. The surface of the bone, above the orbit and from there inward for a short distance toward the median line of the skull, is moderately smooth and shows no trace of a horn core. With the separate posterior crest was found a horn core, similar in shape to, although not as well preserved as, the one belonging to the skull. The posterior crest is composed of the parietals and squamosals coalesced. The former are represented by a flat, thin, smooth median portion that expands laterally both in front and behind anteríorly it is deeply concave below and broadly convex above but posteriorly it thickens gradually and dividing" to either side is continued forward as the squamosals in a broad curve to meet the anterior expansion. On either side of the median element is included a large supratemporal vacuity or fontanelle. The posterior crest is somewhat saddle-shaped. Its sides are wavy, with a slight thickening of the bone in the posterior &amp;filig;ve of the seven corresponding convexities of the periphery, whilst a pair of inwardly directed spurs of bone, with their points turned slightly downward, are developed on its posterior border, one on each side of the median line. The intervacuital element is thickened along its median length and a more decided strengthening of the bone occurs along the posterior border, resembling in this respect the corresponding part of Monoclonms bell-í, described further on. In all other parts of the crest the bone is thin, more particularly near and at the margin of the fontanelles whilst along the sinuous curves of the sides the edge is sharp except in the emarginations where it is rounded. Vascular markings occur on both surfaces, more particularly on the peripheral projections. [table omitted] The skull and the posterior crest were collected on Red Deer river in 1901. With this species are provisionally associated, a scapula and coracoid, a sacrum, an ilium, a rostral bone and a predentary bone, described or referred to in the next succeeding pages. The scapula With coracoid is &amp;filig;gured on plate XIX., &amp;filig;g. 4, viewed from its inner side. The scapula is long and nal'row, slightly concave inward in the direction of its length, stout below, thinning rapidly upward, upper end terminating squarely, breadth decreasing toward mid-length, slightly expanded above, front margin thin, back margin broad below, narrowing‘ to its mid-length then continuing thin upward. A rounded ridge extends upward, on the outer surface, diagonally across from the upper end of the glenoid cavity to the front margin continuing as a decided thickening of the front margin above. The coracoid is broader than high, emarginated below the glenoid cavity and produced backward below, lower border turned inward, inner surface decidedly concave, back border at emargination thick. border elsewhere rather thin, rounded. Foramen traversing thickness of upper part, directed obliquely downward and outward, with an enlarged outer opening. A small foramen occurs, below the glenoid cavity, in the emargination of the posterior border. Grlenoid cavity higher than broad, its curve forming almost a semicircle. In the specimen &amp;filig;gured, the coracoid was probably &amp;filig;rmly united with the scapula, the suture between them, extending from the mid-height of the glenoid cavity forward, being only slightly indicated. The union of the two bones may be regarded as an evidence of in the individual. The left scapula and coracoid from the Red Deer river district, so similar, in most respects, to that of Triceratops prorsus, Marsh, as &amp;filig;gured in the Sixteenth Report of the United States Geological Survey, differs in one important particular, viz., in having the lower border of the coracoid turned inward instead of outward. [table omitted] [table omitted] The sacrum plate XVI, &amp;filig;gs. 1 and 2, is composed of nine coössi&amp;filig;ed vertebrae, of Which seven are true sacrals, the anterior one being a lumbo-sacral and the ninth a caiido-sacral. Viewed from above its general outline is seen to be somewhat triangular, the apex of the triangle pointing forward. The vertebrae have smooth COHCÉLVB sides and niider surfaces and are swollen, Where they coalesce, SO ELS to form a pi'omineiit angularity marking the line as of union. The lower surfaces of the last &amp;filig;ve vertebrae are &amp;fllig;uted by a deep, median, longitudinal groove that extends froin the mid-lengîh of the &amp;filig;fth vertebra backward to its termination in the ninth, the groove being most pronoiinced at the vertebral junctions The &amp;filig;rst eight vertebrae give off seven transverse, intervertebral processes that coalesce distally so as to produce a strong bar Whose outer surface forms the iliac facet. Six openings are thus ileft between the iliac bar, the vertebral centra and the transverse processes. The posterior vertebra gives off a Simple transverse process. The junctions of the second centrum with the third, the sixth with the seventh, and the seventh with the eighth are greatly enlarged by the increased downward GXtension, at these points, Of the neurapophyses fm which the transverse processes spring; particularly is this the case with-the second and third centra. The distance of the iliac facet from the median, longitudinal line of the sac-rum, dependent on the length of the transverse processes and the breadth of the centra, is much greater posteriorly than in front; in its anterior half the facet is directed obliquely downward, possibly With some exaggeration due to distortion in the specimen. The iliac bar at its mid-length bends inward but &amp;filig;nally reaches the &amp;filig;rst vertebra by a convex curve Seen from the side, the iliac bar is horizontal throughout its length With the exception of an upward bend posteriorly. Diapophyses spring from the neural arches above and are connected along the length of their lower edges With the transverse processes. Proximally the superior surfaces of the diapophyses are expanded laterally so as to form a neural platform, the component parts of Which are not coössí&amp;filig;ed. The prezygapophyses remain distinct from the postzvgapo- physes. The specimen has been somewhat crushed in a vertical direction. The diapophyses have acted wedges and have forced apart the halves of the transverse processes near their basal origin. In &amp;filig;gure 17, p. 62, the diapophyses are restored to their supposed proper positions and the neural spines, Whose bases are Well preserved, are indicated, by dotted lines, of aleiigth equal to ‘ that of a spine of a second sacrum of this species, measured in the &amp;filig;eld. The diapophyses are apparently not long* enough to effect a union with the ilium. It is possible that the concave part ofthe iliac facet entered into the formation of the acetabulurn. The articular face of the &amp;filig;rst vertebra is slightly broader than high but in the face of the last vertebra. the excess of breadth over the height is much more apparent the anterior vertebral face is plane, the posterior one is &amp;fllig;at vertically biit concave transversely. Viewed frein the side, the sacrum is moderately arched above but flat below. [table omitted] l' The shortness of the be due in to the rlownward to which the:ipparant diapophyses may a great measure crushing speeimen has been subjected . [table omitted] The rostral bone, &amp;filig;gured on plate XX, and the small predentary bone (plate XIX, &amp;filig;gs. 5 and G) were found separately and may with some probability of correctness be referred to this species. A large iliiim is &amp;filig;gured toward the end of this report. This species is named in honour of Dr. George M. Dawson, C. M. G., late Director of the Geological Survey of Canada.
description: Published as part of <i>Lambe L. M., 1902, New genera and species from the Belly River Series (mid-Cretaceous), pp. 25-81 in Geological Survey of Canada Contributions to Canadian Palaeontology 3</i> on pages 57-63, DOI: 10.5281/zenodo.3233762