"Steneosaurus" obtusidens was first described from the Callovian-aged Oxford Clay Formation of Cambridgeshire, southeastern England on the basis of a partial skeleton (NHMUK R.3168).

The validity of "Steneosaurus" obtusidens was disputed in a 1987 paper reviewing the type specimens of nominal teleosauroid species from the Oxford Clay.

[2] Some authors considered this taxon a probable junior synonym of Machimosaurus hughii based on a subsequently discovered specimen found in Callovian-age exposures in Calvados, Lower Normandy, France, though they stressed that a taxonomic review of blunt-snouted teleosaurids was needed.

[6] Other cladistic and comparative studies agreed with this assessment, recovering "S." obtusidens in a clade with Machimosaurus and Steneosaurus edwardsi.

[7][8][9][10] In 2017, the species was moved to its own genus, Lemmysuchus, referring to Ian Fraser Kilmister, better known as "Lemmy", of the band Motörhead,[11] and the Greek word for crocodile, soukhos.