The type and referred specimens of Plesiosuchus were discovered by John Clavell Mansel-Pleydell in the 1860s alongside the remains of several other large-bodied marine reptiles along the coast of Dorset. Mansel-Pleydell gave these remains to the British Museum (now in the Natural History Museum) in 1866. Part of the holotype of P. manselii (NHMUK PV OR40103a) was first described by John Hulke in 1869. He referred it to Steneosaurus rostro-minor Geoffroy (1825), alongside Dakosaurus maximus and other specimens. Initially, the skull (NHMUK PV OR40103) was believed to be pliosaurian; it was the preparator Mr Davies that suggested a crocodylian nature for the skull. In 1870, Hulke described the skull, which is preserved in two sections: the rostrum and the occiput. Hulke suggested that "this h