The Whitby Mudstone is a Toarcian (Early Jurassic; Falciferum-Bifrons in regional chronostratigraphy) geological formation in Yorkshire and Worcestershire, England.

[1] The formation, part of the Lias Group, is present in the Cleveland and Worcester Basins and the East Midlands Shelf.

The formation consists of mudstone and siltstone, partly laminated and bituminous, medium to dark grey in colour, with rare fine grained calcareous sandstone beds.

[2] Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.

[3][4] One of the more notable discoveries is the skull of the pterosaur Parapsicephalus, found within the Alum Shale[note 2] Member.