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Below are two teeth from the Callovian of the Oxford Clay. The left was identified as Hypsocormus tenuirostris, and the right one Teleosaurus sp. I thought it would be worth verifying both IDs, given how difficult some Jurassic marine reptile teeth are to identify. It is my understanding that @pachy-pleuro-whatnot-odon has great expertise with regards to Jurassic teeth. What do you make of them? Thanks in advance for any guidance Othniel

Hi all, Last summer, while out hunting at the Vaches Noires on the Normandy coast of France, we found the below tooth in the Marnes de Dives (upper Callovian) . I extracted it from its matrix in order to be able to tell with confidence whether carinae are present or not and thus whether the tooth could be metriorhynchid - which I thought, at the time, to be the only other major contender. Carinae are not present. As such, I then arrived at the conclusion that the tooth is plesiosaurian, and in absence of striations - anastomosing or other - that it probably belonged to Cryptoclidus sp.. This is the state in which it has remained since then. From left to right: Muraenosaurus leedsi, Cryptoclidus oxoniensis and Tricleidus seeleyi (Noè, Taylor and Gómez-Pérez, 2017) However, I keep occasionally bumping into Hypsocormus sp., a pachycormiform fish with a temporal range from the Callovian stage of the Middle Jurassic all the way through the Late Jurassic up to the Cretaceous - most recently today with the jaw below. And I must certainly say that I see some semblances... Specimen from the Oxford Clay at Peterborough An unidentified pachycormiform fish tooth from the Oxfordian levels of Vaches Noires (source) that I, here, suggest may, in fact, represent Hypsocormus sp.. Two specimens of Hypsocormus sp. from further up north on the French coast, in the Boulonnais, dating to the Kimmeridgian/Tithonian (source). Given sizes are 6.45mm and 13.1mm respectively. Two Hypsocormus sp. specimens from the Lower Oxford Clay, UK (specific locality unknown; source). Hypsocormus sp. from the Callovian of the Tournus-region of Saône et Loire in France (source). One thing that stands out from all the specimens that I've been able to identify online is that most have an notable acrodin cap, which clearly marks them as fish teeth. It's based on this that I've identified the below tooth from a vendor site as Hypsocormus sp. (or a pachycormiform, at least) tooth, although the seller had listed it as plesiosaur. Thus it seems that confusion surrounding this topic is not uncommon. Unfortunately, however, my specimen is lacking its very apex (though, could this fact in itself be an indication of there once having been an acrodin tip that more easily got damaged or eroded away?)... Pachycormiform tooth mislabelled as plesiosaur, from Fletton, Peterborough Size cannot be used as a distinguishing feature either, as, while my tooth's total length is 1'' or 2.54cm exactly, the enamelled part is only about 1.5cm, which seems to be close to the upper limit of what Hypsocormus sp. teeth were able to grow to, from what I've been able to find out. Ornamentation/striations then? This feature can't be used either, since not all positively identified pachycormiform teeth in my sample have these. How about an in-filled hollow root? Both have these. Though it seems that the pachycormiform teeth actually often lack the enamel-free part you'd identify as the root, with them apparently having broken off close to the enamelled crown, as is the case with most fish teeth. In fact, this was my main argument to reject my specimen being fish before. However, looking at the jaw posted above, you'll notice that the largest tooth lying next to the jaw does have an enamel-free, irregularly broken-off base as well. I thus find myself wondering what the exact features are that define these pachycormiform teeth, and how to distinguish them from reptile teeth. Anybody have any ideas on this or on the argued identification of my tooth? I'll start by tagging @PointyKnight, @RuMert, @caterpillar, @Carl and @taj, but please don't hesitate to join the discussion!