In the talk.origins FAQ "Introduction To Evolutionary Biology" there is a reference to Jurassic brachiopods.
Specifically, the species Kutchithyris acutiplicata is found below the species K. euryptycha. They differ enough that some have argued they should be classified into different genera.
In one small locality, there is a 1.25 meter sedimentary layer where these fossils are found. In the narrow (10cm ) layer that separates the two species, both species are found along with transitional forms.
In other localities, no transitional forms are found, and the species are not found together. The "sudden" transition in those rocks is explained as migration from the place where the transitional forms occur.