On Aristosuchus pusillus (Owen), being further notes on the fossils described by Sir R. Owen as Poikilopleuron pusillus, Owen / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: On Aristosuchus pusillus (Owen), being further notes on the fossils described by Sir R. Owen as Poikilopleuron pusillus, Owen / 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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    though I may think the resemblunco strongest with Ccelurus and Allosaurus, it may be equally strong with Ceratosciurus. But when Prof. Marsh refers pelvic structures so similar as the pubes of Allosaurus aud Ceratosaurus to distinct suborders of the Dinosauria, I can only conclude, if these references are correctly made and sustained, that the pubis is not always a bone on which a generic identification can be based, especially when it is imperfect proxi- mally. I should not thus have ventured to question Prof. Marsh’s reference of this pubis to a genus of his own creation were it not that there is what I regard as strong ground for believing that the sacrum associated with the pubis, no less than the dorsal vertebra figured by Sir R. Owen, belong to a genus which can be but distantly related to Ccelurus. Sir R. Owen, in representing the vertical section of the dorsal vertebra, shows that the centrum is formed of the same kind of tissue, and ossified in the same way as the vertebrae of Dinosaurs in general, except that a fusiform longitudinal space is enclosed which gives no indication of being pneumatic, and appears to open 'into the neural canal. Now, in Ccelurus, Prof. Marsh has defined a genus which, in the construction of its axial skeleton, can only be compared to Ornithosaurs, having the bones invested with a thin film of bone-tissue of uniform thickness and distinctive peculiar texture. This character is as well demonstrated in Marsh’s section of a dorsal vertebra as in the cervical region. Therefore the dorsal vertebrae of Aristosuchus cannot be referred to Ccelurus. Moreover the mode of attachment of the ribs is dissimilar. And hence I submit, as the sacrum of Ccelurus is unknown, there is no reason to suppose that it would be at all like the sacrum of Aristosuchus, which I now describe. There are five vertebrae in the sacrum completely anchylosed together by their neural arches (fig. 13), and either anchylosed or in process of anchylosis by their centrums. Sir R. Owen regards the two posterior vertebrae as sacral, and the three anterior vertebrae as lumbar. Here the difference of interpretation must be adjusted by the definition of the sacrum which is adopted. If the sacral vertebrae are those from which strong sacral ribs are given off for support of the ilium, then no doubt only two such vertebrae can be counted, and the other three vertebrae in which the ilium is more or less supported on transverse processes given off from the neural arch may bo termed saero-lumbar vertebrae. This, however, involves theoretical considerations which cannot be demonstrated, for it is impossible to say how many sacral nerves united into a sacral plexus. And as all the transverse processes have the same trans- verse development (fig. 13, t), and the anchylosis of the vertebrae shows that they took part in supporting the body, I adhere to tho old nomenclature, and regard all the vertebrae which supported the ilium as sacral. I believe the’ anterior vertebrae also contributed to support the pelvic bones, though their share in the work was less than that of the last two. There is a fundamental difference in the plan of structure of the
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