Macropterygius is a genus of ichthyosaurs known from the Late Jurassic (Kimmeridgian age) of England (Kimmeridge Clay formation).

It has had an unstable taxonomic history, partly because the species was originally named without designating any particular specimen as the holotype.

This created a problem, because the vertebrae selected by Lydekker came from unknown sediments and were not definitely associated with the original specimens named and described by Owen.

Matters were complicated when the original holotype used by Owen was re-discovered, making the designation of a neotype unnecessary.

[3] In 2000, Bardet and Fernández found that the holotype specimen of Macropterygius trigonus is undiagnosible beyond the level of Ophthalmosauridae, thus this genus and species were considered nomina dubia.