Monoclonius dawsoni, Lambe, 1902

Lambe L. M., 1902, New genera and species from the Belly River Series (mid-Cretaceous), Geological Survey of Canada Contributions to Canadian Palaeontology 3, pp. 25-81 : 57-63

Monoclonius dawsoni . Sp. nov.

Plate XVI , plate XIX, figs. 4 - 6 , and plate XX, figs. 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 definite 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 filling the space between the orbit and the horn core (see fig. 14, from a measured drawing made before the parts of the skull were removed).

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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 five 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.

Measurements.
	M;
Height of orbit.	llo
Width of orbit.	' 095
Height of horn core.	' 331
Circumference at base ot horn core.	' 343
Antero-posterior diameter of base of same.	‘ 135
Transverse diameter of base of same.	' 092
Diameter of occipital condyle	‘ 060
Length of maxilla approx.	' 350
Height of same.. approx.	120
Long diameter of lower face of quadrate.	' 080
Short diameter of lower face of quadrate.	‘ 036
Posterior crest
Extreme length from anterior end of speeimen (imperfect), medially, to line
touching posterior edges of specimen on either side.	‘ 616
Length on median line from anterior end to posterior border...	' 486
Semi-breath of specimen on curve of under surface..	' -170
Semi-breath of specimen horizontally.	"439
Vertical drop of lateral edge of specimen below median line of under surface
at mid-length.	157
Antero-posterior diameter of fontanelle ..	‘ 296
Transverse diameter of fontanelle.	' 248
Circumference of base of left posterior spur ..	' 172

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 figured on plate XIX., fig. 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 figured, the coracoid was probably firmly 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 figured 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.

iUeas-ztrenzents of scapula and coracoid.
	N
Scapula with coracoid (left). Cat. No. 506.
Extreme length of scapula with coracoid in line with back edge of shaft..	' 879
Length of scapula	"711
Length across glenoid cavity	‘ 150
Length of glenoid cavity, along curve.	' 204
Breadth of glenoid cavity at suture between scapula and coracoid	"078
Breadth of glenoid cavity near either end	‘ 096
Breadth of scapula at junction with coracoid,‘ inner surface.	175
Breadth of scapula at junction with coracoid; outer surface.	' 149
Breadth of scapula at upper end of glenoid cavity.	" 238
Breadth 0 f scapula at mid-length	113
Breadth of scapula at upper end..	' 184
Breadth of coracoid at lower end of glenoid cavity	' 223
Thickness of scapula at upper end near front border.	' 025
Thickness on base of ridge above upper end of glenoid cavity.	‘ 060

Thickness at lower end of glenoid cavity	*060
Thickness of coracoid in coneavity below forainen.	*020
Width of foranien; inner end.	014
Height; inner end	- 030
*025
Height of same; outer end	*040

The sacrum plate XVI, figs. 1 and 2 , is composed of nine coössified 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 five vertebrae are fluted by a deep, median, longitudinal groove that extends froin the mid-lengîh of the fifth vertebra backward to its termination in the ninth, the groove being most pronoiinced at the vertebral junctions The first 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 finally reaches the first 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 coössífied. 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 figure 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 field. 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 first 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 flat vertically biit concave transversely. Viewed frein the side, the sacrum is moderately arched above but flat below.

Measurements
	M.
Extreme iengiit of sacrum (302 inches).	' T 66
Basal 1011D"lll of Ist vertebra	' 084
“ 2 nd	102
“ “ 3 rd	' 085
1 í (í 4. h	092
“ 5 th	' 086
“ " 6 th	*088
I bll	*ess
“ “ 8 th	' 078
“ Ot-li	' 063
Height of articular face of 1 st vertebra	llo
Breadth of saine	123
Height of articular face of 9 th vertebra.	108
Breadth of same.	' ISO

.

Antero-posterior' diameter of base of neural spine of 2 nd vertebra.	' OTC
. c L: c: LL L: LL grd cc	081
LL L::L:L cc L: 4 th	092
LL L: L::L 5 th cc	085
LL LL:L LL L: 6 th LL	077
LL LL:L:L 7 th cc	070
Length of iliac face along its curves.	' #358
“ “ “ in straight line. a
Breadth of same at its anterior end	"075
“ “ “ mid-length	' 056
' 04- 5
Breadth of lst vertebra at mid-height of its concave sides	' 103
C‘ 2 nd CC l‘ CC	096
‘C 3 rd C‘ CC CC	079
CC 4 th C‘ l‘ CC ‘C	u 072
CC 5 th CC k‘ CC ‘ C	073
cc 6 th:L LL L: LL	- 083.
CC 7 th CC C‘ K‘ ‘C	ı 150
Breadth at junction of 8 th with 9 th vertebra.	' IST
Distance from centre of neural canal to distal end of diapopliysis of 2 nd vertebra.	118
Distance to same of 3 rd vertebra.	‘ 115
(c LL 4th LL	. 1 1 2
CC l‘ 5 th CK	ı 1 1 9
“ “ 6 th i‘	" 135
:L L: 7 th c:	. 1 95

The rostral bone, figured on plate XX , and the small predentary bone ( plate XIX , figs. 5 and G) were found separately and may with some probability of correctness be referred to this species. A large iliiim is figured 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.

Figures

PLATE XVI. Fig. 1. Sacrurn, provisionally associated with Monoclonius dawsoni, Laınbe, superior view; two-sevenths the natural size. Page 61. Fig. 2. The same, viewed from the right.

PLATE XIX. Fig. 1. Myledaphus bipartitus, Cope, pavement tooth, face of crown; enlarged four times. Page 28. Fig. 2. Side view of same tooth. g, crown; f, face of crown; r, root. Fig. 3. Lepidotus occidentalis, Leidy, outer surface of scale natural size. Page 29. Fig, 4. Monoclonius dawsoni, Lambe, lcft scapula and coracoid, internal view. (Provisionally associated with M. dawsoni); onefourth natural size. Page 60 Fig. 5. Monoclonius dawsoni, predentary bone, lateral view. (Provisionally associated with M. dawsoni); natural size. Page 63. Fig. 6. The same, viewed from above. s scapula; c coracoid; a, suture between scapula and coracoid; g, glenoid cavity; b, upper,, border d, anterior end; e, groove for dentary.

PLATE XX. Fig. 1. Monoclonius belli, Lambe, parietal element of posterior crest, superior view; one-third the natural size. Page 66. Fig. 2. The same, inferior view. Fig. 3. Monoclonius dawsoni, Lambe, rostrai bone, side view; one-half the natural size. (Provisionaily associated with M. dawsoni). Page 63. Fig. 4. Outline of section of at “. ” same c Fig. 5. Horn core with an asymmetrical base. Kot specifically determined. Fig. G. Sectional outlines of same at a and h” g, groove for premaxilla

FIG. 16.-—Sacriiiri provisionally associated with Monocloni us dawsoni, less than one-seventh the natural size 2 superior view.