Dykeius is an extinct genus of large shark in the family Chlamydoselachidae.

It contains a single known species, D. garethi, from the Late Cretaceous Northumberland Formation of Canada.

[1] It was a gigantic relative of the modern frilled shark (genus Chlamydoselachus).

The teeth are much larger than those of any other known chlamydoselachid species, and comparison with modern frilled sharks estimates a total body size of at least 7 metres (23 ft).

It may have been specialized to hunt large cephalopods such as certain belemnites and ammonites, and eventually went extinct due to the disappearance of its prey.