On the os pubis of Polacanthus foxii / by H.G. Seeley.

  • Harry Govier Seeley
Date:
1892
Catalogue details

Licence: Public Domain Mark

Credit: On the os pubis of Polacanthus foxii / 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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    verse position vertical above the femur, and is in a way imperforate. It is noticeable that, while the sacral ribs form 5 lateral but- tresses to support the acetabular part of the ilium, several pre- sacra] ribs (in no way modified) extend between the external armour and the ilium, for the more anterior are seen through the thin pre-acetabular plate of the ilium. And this indicates that armour, ribs, and ilium blended late in life. There is a very close resemblance in the ilium between Pola- canthus and Omosaurus; for Omosaurus has a similar large hori- zontal acetabulum, while the pre-acetabular plate is of similar form, and extends horizontally forward and outward, and the post- acetabular part is similar. There is also a manifest resemblance in the forms of the sacral ribs, and in their mode of attachment to the sides of the vertebrae to which they belong, although in Pola- ennthus they tend to a slightly more anterior position. In Omo- saurus, however, external armour on the trunk is unknown. Other resemblances to Polacanthus are found in the Gosau fossil Cratceomus. When that type was described in 1881 I had not seen any of the remains of this armoured Wealden fossil. But I drew attention to a figure by the late Mr. J. E. Lee 1 from the Wealden of the Isle of Wight, which shows a dermal plate with tubercles upon an osseous base, as similar to armour of Cratceomus.2 Mr. Lee’s fossil may have belonged to Polacanthus or a nearly allied genus. The dorsal vertebra of these genera are very similar, as is evident on comparing Phil. Trans. Boy. Soc. 1881, pi. lxx., and Quart. Journ. Geol. Soc. vol. xxxvii. pi. xxx. fig. 3. The femur in both corresponds in type and in many details. If there had been any grounds for referring the remarkable plates to Cra- tceomus 3 which Bunzel had figured as the ilium of Danubiosuurus the resemblance might have been carried further. It has been shown that those remains consist of a rib-like lower part, with which is blended a superimposed thick smooth armour, like that of a Chelo- nian. Without re-examination it may not be possible to form a definite judgment on these remains, but there seems some likelihood that they may prove to be portions of the ilia of Cratceomus with confluent smooth armour extending forward from the acetabulum. Polacanthus, however, has no such smooth scutes, and all the armour of Cratceomus which can be compared with it is either tuberculate or rugose with vascular impressions. Ornithischians with smooth armour, however, existed in tho Wealden deposits. And the British Museum acquired in the Beckles Collection a portion of the acetabular region of such a fossil which differs from Polacanthus in the far greater thickness of the ilium above the acetabulum, in the forms of the confluent sacral ribs constricted from front to back, and in the absence of all trace of ornament from the smooth and relatively thin dermal shield above the ilium as preserved. The species is larger than 1 Ann. Mag. Nat. Hist. vol. xi. (1843) pi. i., and ‘ Note-book of a Naturalist.’ 2 Quart. Journ. Geol. Soc. vol. xxxvii. (1881) pi. xxviii. 3 Ibid. p. 6114.
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