It was collected from the A. bifrons ammonite zone of the Whitby Mudstone Formation, dating to the early Toarcian age, about 183 to 180 million years ago. The complete skeleton which preserved the skull, NMING F8785, was kept for five years at Mulgrave Castle, which was then owned by the Marquess of Normanby. In 1853, the Marquess introduced the interesting finding to the eminent Irish surgeon and anatomist, Sir Philip Crampton.
The ammonite fossil, discovered in the A. bifrons ammonite zone of the Whitby Mudstone Formation during the early Toarcian age (about 183 to 180 million years ago), was kept at Mulgrave Castle for five years before being presented to Sir Philip Crampton, an eminent Irish surgeon and anatomist.