El Doctor Formation

The El Doctor Formation is a geologic formation in Mexico. It preserves fossils dating back to the Albian and Cenomanian stages of the Cretaceous period.
Description.
The light grey micritic limestone sequence with intercalated black chert lenses was deposited in an open marine basin with a hypersaline and/or poorly oxygenated bottom.
Fossil content.
The formation has provided the following fossils: