On associated bones of a small anomodont reptile, Keirognathus cordylus (Seeley) : showing the relative dimensions of the anterior parts of the skeleton, and structure of the fore-limb and shoulder girdle / by H.G. Seeley.

Harry Govier Seeley

Date:: 1888

Credit: On associated bones of a small anomodont reptile, Keirognathus cordylus (Seeley) : showing the relative dimensions of the anterior parts of the skeleton, and structure of the fore-limb and shoulder girdle / by H.G. Seeley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

4/22 page 488

$measurement from the occipital condyle to the extremity of the snout is 8‘5 centims. The vertical measurement from the condyle of the quadrate bone to the summit of the skull is 6 centims., and it is 7 centims. from the infra-articular angle of the lower jaw. The lateral contour of the skull closely approaches that of Dicynodon feliceps; but that species has the squamosal bone longer, the lower jaw deeper, the maxillary tooth larger, and the back of the head apparently less elevated. Dicynodon dubius has the tooth as small as in this specimen, but its root enlarges in the skull, in a way to which this species shows no approximation. Only in Dicynodon recurvidens is so small a tooth found as appears to characterize this fossil; but the skull of that species has little in common with these remains. Hence I conclude that the head upon the slab belongs to an undescribed species, with the facial contour of D. feliceps; a short vertical quadrate region, as in D. dubius; and small teeth, like those of D. recur- videns, which, however, were directed downward and forward instead of downward and backward. The scapula shows it to be related to Kistecephalus; but the humerus distinguishes it from other genera. From the back of the head the contour line steadily descends as it extends forward, till over the anterior border of the narine the descent to the alveolar margin becomes rapid. The shape and size of the narine are badly indicated, but its dimensions as preserved are about 17 millims. long by 13 millims. high ; hence, the form of the aperture was probably transversely ovate, and its size smaller than the present fractured limits of its margin. It approached near to the roof of the snout, and its superior margin was about 23 millims. above the margin of the jaw, at the point where the tooth crosses it. The orbit appears to have been relatively small, less than 1'5 centim. in diameter. It is separated from the narine by a bar which is less wide than the narine, and is undefined posteriorly, since the post-orbital bar is broken away, leaving a long transversely ovate vacuity, which extends over the temporal region, and measures about 4'5 centims. long by 2'7 centims. deep. The alveolar margin of the jaw forms a sigmoid curve, being concave from the quadrate bone forward, then convex, with the convexity terminating behind the extremity of the jaw. The small tooth, of which only a fragment is preserved in situ, is in advance of the middle of the convexity at 2'5 centims. behind the imperfect anterior extremity of the jaw. By the side of the anterior extremity of the lower jaw is what I take to be an impression of a tooth, which is 3 millims. wide and 17 millims. long. The tooth itself may have been longer and wider. These remains may be parts of the same tooth, with a crown fully 2 centims. long ; they give no evidence of expansion of the root to a wide pulp cavity, as in Dicynodon. The vertical depth of the head between the orbit and narine is about 4 centims. in the anterior convex part of the alveolar border; and the depth is about the same in the middle of the posterior concave part of the border. This curved outline of the border of the jaw probably results from the breaking away of the maxillary bone, for the pterygoid bone is exposed posteriorly, and is seen to extend downward and unite$