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Hi all, I've had the below piece in my collection for a number of years now, having acquired it thinking it was a juvenile plesiosaur propodial. It comes from the Oxford Clay of Peterborough and is of Callovian Jurassic age. However, when recently doing some research towards answering another question on TFF, I realised that - even though there's some plastic deformation going on - it doesn't quite look like the juvenile plesiosaur propodial I have from the rhaetic at Aust, nor does it look like a plesiosaur propodial in a more general sense (see both post and images below). There are some oddities that have started to make me wonder, in not a plesiosaur propodial, what else it may be in that case. The bone is quite dense, so is definitely marine reptile. And, since I'm quite sure it's not ichthyosaurian, this, I believe, leaves only pl(es)iosaur and teleosaur. Morphologically, the bone consists of a shaft that widens towards one end, with the other end having broken off. The widened end, top-side, forms a bit of an overhang across what appears to be an intact articulation surface, with a notch cutting into it from the right. At the broken end, also on the right, there appears to be a slight twist in the bone. This is, moreover, the side that's rounded along the length of the bone, whereas the other side appears carinated. Although there's some crushing on the underside of the bone, that surface appears markedly more flat than the obverse. It is primarily the facts that one of the edges is (more) angular and that the bone thickens towards the widening end - rather than thins out, as in a typical plesiosaur propodial - that make me feel this is not a plesiosaur (sensu lato) propodial. Unfortunately, I don't have enough qualitative reference material on teleosaurs myself (some images below) to evaluate whether they could be a candidate for the bone - such as long or girdle bones - and didn't find anything matching amongst the figures in Johnson, Young, Steel and Lepage (2015) or Young, Sachs & Abel (2018) either. So I'm left thinking may be it could be a plesiosaur ilium, as in the other post referenced above. There are definitely some features that seem to argue in its favour, such as the flat back, slight twist and widening distal end. But lacking the proximal end of the bone makes it harder to judge, and the thickening of the bone towards the widened part seems to conflict with the idea of the bone being an ilium. Still, there are very few flat narrow bones in a plesiosaur outside of its extremities... Machimosaurus sp. at the Museum voor Natuurwetenschappen in Brussels (source: Wikipedia) Thoracic region of Machimosaurus sp. at Paléospace l'Odyssée at Villers-sur-Mer Metriorhynchus superciliosus at the Paläontologische Summlung MUT Tübingen Thoracic region of Steneosaurus sp. at the Fossilienmuseum Dotternhausen Steneosaurus spp. specimens at Urweltmuseum Hauff in Holzmaden Steneosaurus sp. leg bones at the Paläontologische Sammlung MUT Tübingen