Rare Cretaceous ichthyosaur from Lincolnshire

John P Green (UK) As many amateur and professional palaeontologists are aware, ichthyosaurs are well-known aquatic reptiles from the Mesozoic era, which are especially common in Jurassic marine deposits in the UK. They are particularly conspicuous in the Charmouth and Whitby Mudstone Formations of the Lias (Lower Jurassic), as well as the Oxford and Kimmeridge Clay Formations (Upper Jurassic). These horizons have yielded numerous complete and fragmentary remains that grace many private and museum collections across the UK. By contrast, the record of ichthyosaurs in Britain from the Jurassic/Cretaceous boundary interval is somewhat scanty, and only rare and fragmentary remains having been discovered. Any remains discovered from this time interval are therefore of great potential significance. Back in August 1995, during one especially hot summer’s day, I was fortunate to discover fragmentary ichthyosaur remains at a small quarry at Nettleton, Lincolnshire. This quarry exposed the Lower Spilsby Sandstone Formation, which is a shallow water marine deposit that embraces the Jurassic/Cretaceous boundary interval in Lincolnshire (Gaunt et al, 1992). Fig. 1. Locality map of the Castle Top quarry. Reproduced from Green and Lomax 2014; image originally reproduced. by permission of the council of the Yorkshire Geological Society. The specimen was discovered at a single horizon, 3.5m above the base of the formation, which (based upon stratigraphical grounds) falls within the ammonite zone, Subcraspedites preplicomphalus (Casey, 1973). This was formerly considered to fall within the Volgian stage of the latest Jurassic (Gaunt et al, 1992), although more recent work by Hopson et … Read More

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