This is a vertebra from a large Ichthyosaur that would have been about seven metres in length. It was probably the species Temnodontosaurus platyodon.
We know that this vertebra has come from towards the tail of the animal because the rib facets, the point where the ribs articulate with the vertebrae, are quite low down the side of the vertebra. The side nearest to the ‘front’ as photographed, is the top of the vertebra. The groove is where the spinal cord ran along the vertebra enclosed within the neural arch.
Find out more on the reptiles pages.