Aristodesmus rütimeyeri (Wiedersheim) / H.G. Seeley.

  • Seeley, H. G. (Harry Govier), 1839-1909.
Date:
1900
Catalogue details

Licence: In copyright

Credit: Aristodesmus rütimeyeri (Wiedersheim) / 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.

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    Vol. 56.] ABISTODF.S.MPS RUTIMETERI. f>21 slabs. Accordingly, in the following description I rely upon impres- sions of bones, taken by myself from such parts of the skeleton as would manifestly yield prints without the possibility of injury to the matrix. These impressions suggest modifications of Prof. Wiedersheim’s osteological interpretations of the bones. What was regarded as the humerus, I describe as the interclavicle. The scapula of Wiedersheim’s fig. 1 is the humerus; the supra-scapula in his fig. 2 is the left coracoid; but in fig. 1 it is the right scapula. The bones interpreted in 1878 as right and left coracoids are the precoracoid and coracoid of the right side of the shoulder- girdle. The bones named clavicles are ribs. A row of teeth drawn upon the palate in the restoration, is doubtfully indicated in the specimen. In place of the four digits to the hand, 1 find indications of five. These modifications of interpretation reopen the question of the animal’s organization. The only alternative supported by evidence of structure is, whether the remains should bo referred to a Triassic mammal, or to an Anomodont reptile. Against a mammalian interpretation is, firstly, the presence of a large parietal foramen; and secondly, a composite structure of the lower jaw. There is also the presence of prefrontal, and perhaps postfrontal, bones in the skull, though as the external surface has been chiselled away the evidence on these points is not complete; and at the close of this paper evidence is adduced to show that those bones are found in Ornitho- rhynchus, together with a reptilian structure of the malar arch. The Anomodont structure may be affirmed, firstly, on a general resemblance of the skull to the skull in Procolophon ; secondly, there is absolute correspondence of the shoulder-girdle with that region in Anomodont types, and a close approximation to Procolophon ; thirdly, the great transverse expansion of the proximal and distal ends of the humerus, which, like tho shoulder-girdle, is only paralleled in Anomodonts and Monotremes ; fourthly, a general correspondence of the vertebrae in plan, and especially in the articulation of the ribs, with Pareiasanrus and Echidna; fifthly, the Anomodont form of the pelvis, without an obturator-foramen between the ischium and pubis, or a perforation in the acetabulum ; sixthly, the close paral- lelism in form of the femur to Echidna; seventhly, the general resemblance of the tibia and fibula to those of Pareiascturus ; and, eighthly, the structure of the tarsus, where the proximal row consists of a single bone formed from the anchylosed astragalus and os calcis. The most distinct approximations to Procolophon are tho un- anchylosed condition of the bones of the shoulder-girdle and pelvis ; and the form of the skull, and smooth condition of the skull-bones. In so far as the fossil diverges from Procolophon and Pareiasanrus*, it approximates to Echidna, especially in the characters of the limb-bones, such as the humerus, ulna, femur, fibula, and proximal elements of the tarsus. As the genus is new, tho fossil may be known as Arisloclesmus llutimeyeri (W i e de r sh ei m). Q. J. G. S. No. 223, 2 t