Further observations on Pareiasaurus / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: Further observations on Pareiasaurus / 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.

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    remarkable Elasiiiosaurian types of Sauropterygia from the Oxford clay, grouped unde]- Murcenosaurus. There is no trace of any close correspondence to this kind of shoulder girdle in existing reptiles. The clavicular arch finds its nearest parallel among Labyrinthodonts, owing to the apparent possession of the epi-clavicles or supra-clavicles seen in genera like Actinodon, described by Professor Gaudry. Tbe clavicular arch of Eryops in the relative development of clavicle and inter-clavicle, together with the scapular arch in contact with it, as figured by Professor Cope, offers by far the nearest parallel to Pareiasaurus. That type at present has not been demonstrated to be Labyrinthodont, and I con- ceive that it may be not improbably included within the Pai'eiasauria, partly on the evidence of its pelvic characters, but also on evidence of the shoulder girdle, limbs, and, to a less extent, of the vertebral column. Everything depends upon the characters used for classification. The relations of the coracoid, precoracoid, and scapula towards the humeral articulation, seem to me to make a more useful basis for classification than the imperfect ossification of the vertebrae or size of the inter- centrum ; and the anterior direction of the ilium, with its posterior angle, and the median symphysis of the pubis and ischium, which parallels the condition in Pareia- saurus and other Anomodonts, I can only account for by referring Eryops to the Peptilia, and provisionally to the Pareiasauria. The Vertehral Column in Pareiasaurus Baini (Plates 17, 23). There appear to be eighteen presacral vetrebrm. The distinction between cervical and dorsal region is not well marked, but ten vertebrae may perhaps be counted as cervical and eight as dorsal in Pareiasaurus Baini. The characters of the cervical vertebrae are not completely shown, owing to attachment of ribs and matrix. The first two vertebrae were completely embedded in the matrix at the back of the head. The atlas as jjreserved is represented by a centrum, which is little more than two- thirds the dimensions of the same element in succeeding vertebrae, its neural arch is not in contact with the centrum. In the specimen figured (‘Phil. Trans.,’ 1889, B., Plate 12), as Dicynodon {Tropidostoma) Dunni [loc. cit., j). 250), the first vertebra free from the skull was described as not having a neural arch. That specimen appeared to have an ossification, which is longer than a vertebra, between that centrum and the back of the skull.'' The anterior face of the atlas in Pareiasaurus Baini is small and somewhat convex, for adaptation to the cup of the occipital condyle. The measurement from front to back is about inch. There is a groove in the position, which I take to correspond to the neural canal. The bone is transversely ovate, being 3f inches wide and 2f inches deep. The absence of the anterior articular cup is a remarkable difference from the usual condition in extinct Peptilia, and so far as it goes is rather suggestive * By removing the cervical vertebrae from the skull two vertehr® were found in this position, while their mode of union with the skull is dissimilar to anything previously known.