Stereocephalus tutus, 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 : 55-57

Stereocephalus tutus . Sp. nov.

Plate XI , plate XII, figs. 1, 2, 3, 4 and 5 , and plate XXI, figs. 6, 7 and 8 .

The speeimen of Which views from above, from the side and from below are given on plates XI and XII, represents part of the plate-protected cranium of a herbivorous dinosaur, that is, apparently, quite distinct from any hitherto described.

With the head was found a transverse series of coössified sharply keeled scutes which will be described farther on.

The part of the head preserved is strongly convex transversely, but only moderately so from front to back. Goôssified plates cover the whole of the upper surface and are continued down on the vertical sides. They are arranged with a certain amount of bilateral symmetry, are quite small at the centre and toward the back, but are larger in front and very much more so on the sides. They are for the most part irregularly five or six sided, with rather undulatory surfaces that are marked by an irregular, raised, structural cross-hatching, feebly suggestive of the surface markings of the plates of Nodosaurus textilis, Marsh. Small vascular openings and grooves are also numerous on the surface. The edges of the plates are as a rule angular and sometimes raised. Each plate has its limit defined by a deep circumscribing furrow, so that although they are coôssified and form a continuous surface covering to the head, they do not lose their individuality. A rounded node, or an incipient keel is noticed on some of the plates.

The removal of sandstone from the lower surface of the specimen revealed the bones of the palatal region ( plate XII . fig. 2). The interpretation of these elements are as indicated by the letters. The back ends, only, of the palatines (P) are seen, meeting the pterygoids in a suture indicated at “ s. From here the latter bones (pt.) extend backward on either side of interpterygoid vacuities (v.). The ridge (pb.) represents the presphenoid and basisphenoid elements; it is bent posteriorly to one side in the specimen, which has been subjected to considerable pressure from above and is somewhat crushed behind.

From this intel'pretation of the bones of the palate it would appear that the part of the armature preserved covers the upper part of the head near the union of the nasals With the frontals. No indication of the 01'bits can be detected and it is probable that they were placed far forward in the head.

Ãfeasurevnents.
		M.
Antero-posterior diameter of speeimen.		‘ 250
Greatest transverse diameter.		' 210
Height of centre of upper surface above the level.		1225
about.	‘ 040
Maximum thickness of cranial armature.	. about about	' 016

With the 11ead,just described, Were five keeled, bony scutes or plates that have since been found to fit together in the form of an arch ( plate XII , figs. 3 and 4), Whose sides curve forward as well as (lownward. This oblique curve places the lower, paired scutes, as seen when the arch is viewed from above, a little in advance of the upper pair which is again slightly in advance of the median plate

The scutes rest on and are ossified to a thickness of bone that constitutes the inner, continuous surface of the arch. This band of bone, ornamented above by paired ossicles, suggests the possibility of its being the back border of the posterior crest of the species to which the head armature, above mentioned, belonged.

This suggestion is given credence from the fact that the concave edge of the band of bone on which the scutes rest is fractured, whilst the convex edge appears to be intact.

Numbering the ossicles from the right, the junction between Nos. 1 and 2 was perfect, as were also those between Nos. 3, 4 and 5, but iii the case of Nos. 2 and 3 the fractured edges did not fit with sufiicient exactness to remove all doubt as to their being placed side by side, although the continuity and symmetry of the curve of the under surface seemed complete. It is possible that one or two scutes are missing froın between Nos. 2 and 3, especially as fragments of similarly shaped scutes were found at the same spot. If an additional soute completed the series it probably would have been the mate of the present median one, or if two were required to fill the gap (if such a gap exists) one would be on the median line, the other would correspond with No. 3 to form another pair. The addition of one or two scutes to the series would result only in extending and possibly flattening the curve.

The median sente is apparently symmetrical, the others are asymmetrical, forming pairs with reversed lateral proportions.

The scutes have an irregularly oval basal outline, are sharply keeled, with sloping sides shallowly excavated from the keel downward but convexly curved from front to back, their basal edges are defined by an engirdling furrow below which, at a lower level, they are laterally expanded to meet each other in a plane surface. A very small ossicle rises above this intermediate basal surface between Nos. 3 and 4. Vascular markings are conspicuous on the sides of the scutes.

fllezısurenıents of transverse series of scutes.
	M
Height of apex of median keel above the level.	190
Height of centre of inner surface of arch above the level.	125
Width of inner spread of arch below	' 236
Average height of apices of keels above inner surface of arcli	' 072
Basal breadth of the seutes (Nos. 2 and 4) on either sidc of the median one.	' 075
'Basal length of same.	143
Thickness of bone on which the scutes rest, about.	' 010

Belly River series, Red Deer river, 1897.

The tooth shown in fig. 12, is of the Stegosaurían type. It differs from those, of the Red Deer river district, referred to the two species of Palœoscincus, and is about twice as large as those of P. costatus. 1 t is figured here with the idea that it may eventually prove to belong to S. tutus. It was collected below Berry creek, on Red Deer river, in 1901.

A spinous dermal plate of massive proportions, fig. 13, A and B, is referred to this species on account of its similarity, in structure and surface markings, to the postcranial keeled scutes described above. This specimen was collected in 1897. Another large plate similar in general proportions to the above and nearly as large, as Well as numerous others of different sizes and of a variety of shapes, were collected in 1901.

Figures

PLATE XI. Stereocephalus tutus, Lambe, head armature, superior view natural size. The anterior end of specimen points downward. Page 55. a, anterior end.

PLATE XII. Fig. 1..Stereocephalus tutus, Lambe, view of left side of specimen figured on plate XI one half the natural size Page 55. Fig. 2. Palatal view of the same one-half tho natural size. Fig. 3. Stereocephalus tutus, coössified postcranial scutes, superior view two sevenths the natural size. Page 56. Fig. 4. The same, anterior view. Fig. 5. Transverse section of rib (provisionally associated with S. tutus; one-half the natural size.) Page 55. p, palatine; s, suture pt, pterygoid; z‘, inlerpterygoid vacuity pb, prosphenoid and basisphenoid element; a, anterior b, posterior.

PLATE XXI. Fig. 1. Stegoceras validus, Lambe, prenasal bone; side view. Natural size. Page 63. Fig. 2. The same, inferior aspect. Fig. 3. Superior view of another specimen; natural size. Fig. 4. The same; side view. Fig. 5. The same; inferior view. Fig. 6. Stereocephalus tutus, Lambe, symmetrical plate, superior aspect; one-half the natural size. (Pro. visionally associated with S. tutus). Figs. 7 and S. Similar keeled plates one-half the natural size. Fig. 9. Shield of Acipenser albertensis, Lambe, viewed from above. Natural size. Page 29 .

PLATE XXI. Fig. 1. Stegoceras validus, Lambe, prenasal bone; side view. Natural size. Page 63. Fig. 2. The same, inferior aspect. Fig. 3. Superior view of another specimen; natural size. Fig. 4. The same; side view. Fig. 5. The same; inferior view. Fig. 6. Stereocephalus tutus, Lambe, symmetrical plate, superior aspect; one-half the natural size. (Pro. visionally associated with S. tutus). Figs. 7 and S. Similar keeled plates one-half the natural size. Fig. 9. Shield of Acipenser albertensis, Lambe, viewed from above. Natural size. Page 29