Monday 18 August 2014

Mr. Lee's dermal plates: the first Polacanthus?

The illustration from Lee's report of 1843 of a single osteoderm and surrounding ossicles.

The first sign that there was an armoured dinosaur present in the rocks of Wealden Sub-Basin of the Isle of Wight was when one John Edward Lee reported the existence of three fossils from the Hastings Beds of Sandown on the Isle of Wight way back in 1843. However, the Hastings Beds don’t outcrop on the island, so if they didn’t actually come from there where did they come from? Lee describes these fossils as ‘dermal plates’, and goes on to describe them at length in his paper. Only one is illustrated however, and this and the second plate were sent to Mr. Sowerby (presumably this is James De Calre Sowerby, a mineralogist and illustrator who co-founded the Royal Botanical Society and Gardens) in a hackney carriage along with drawings of the fossils destined for publication in the Annal of Natural History. The third was in poor condition and not deemed worthy of illustration and is still held in the Natural History Museum, London (BMNH R643) according to Pereda-Suberbiola. The surviving illustration clearly shows a single large osteoderm surrounded by smaller ossicles, themselves set amongst more ossicles. This certainly looks like a section of Polacanthus sacral shield, but is it?

The holotype of Polacanthus was found by the remarkable Rev. Fox of Brixton (now Brighstone) on the Isle of Wight around 1865. Fox had found the shield intact but it crumbled as he excavated the specimen, and when J.W. Hulke finally got around to describing the fossil in 1881 the shield was still in numerous small bits. Five years passed and Hulke revisited Fox’s Polacanthus, the shield of which had been reconstructed piece-by-piece by the remarkable efforts of a Mr. Hall and Mr. Barlow. This revealed the ornamented upper surface of the shield which Hulke describes in some detail, including the arrangement of larger keeled osteoderms amongst smaller ossicles, very similar to Lee’s specimen. Polacanthus is not the only nodosaurid (if Polacanthus is actually a nodosaurid, but that’s another story) with a sacral shield, and a comparison via the literature with sister taxa such as Mymroopelta and Gastiona reveal their sacral shields were similarly ornamented (see illustration below).

A selection of osteoderms and ossicle arrangements from various nodosaurids.
Lee's specimen is top right, the others are redrawn from various papers.

It’s likely that Lee’s specimens were the first remains of a Polacanthus sacral shield ever reported. As was mentioned earlier, the fossils probably didn’t come from the Hastings Beds as they aren’t present on the Isle of Wight; Pereda-Suberbiola suggests these remains are from the Wessex Formation at Brook Bay (Pereda-Suberbiola, 1994), although a part of the Wessex Formation is exposed in the cliff at Sandown and he doesn’t give his reasons for favouring this location. As for the fossils themselves, Lee was an astute observer and commented on the histology of the osteoderms, recognising the fibrous nature of the bones. He compared them with the scales of extant iguanas and crocodilians, and despite the fragmentary nature of the material found no reason to connect them with lizards or crocodiles.

The two ‘plates’ and drawings never made it to Sowerby. They were sent in a hackney carriage but never arrived and so joined the list of other dinosaur specimens lost to science. Had they had done, it’s entirely plausible that Polacanthus would have been named twenty years before it actually was.


Hulke, J.W. 1881. Polacanthus foxii, a large undescribed dinosaur from the Wealden Formation in the Isle of Wight. Philosophical Transactions of the Royal Society of London, Vol. 172; 653-662.

Hulke, J. W. 1887. Supplemental note on Polacanthus foxii, describing the dorsal shield and some parts of the endoskeleton, imperfectly known in 1881. Philosophical Transactions of the Royal Society of London, Vol. 178: 169-72.

Lee, J.E. 1843. Notice of Saurian Dermal Plates from the Wealden of the Isle of Wight. Annals of Natural History. London. 11: 5-7.

Pereda-Suberbiola, X. 1994. Polacanthus (Ornithischia: Ankylosauria), a transatlantic armoured dinosaur from the Early Cretaceous of Europe and North America. Palaeontographica, Abteilung A, 232: 133–159.

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