Invertebrate fossils
Cretaceous oysters
Thick, gnarled oyster shells (typically Exogyra and Pycnodonte) that paved the floor of the Late Cretaceous seaway. Their durable calcite preserves them better than almost any other invertebrate — you'll find them in nearly every Cretaceous creek bed on the East Coast.
How to spot it
- ▸Heavy, thick-walled — much chunkier than modern oyster shell
- ▸Strongly curved or coiled (Exogyra) or rounded and flat (Pycnodonte)
- ▸Concentric growth rings are usually preserved on the outside
- ▸Often show borings from sponges or clionid sponges (round 1–2 mm holes)
- ▸Color ranges from pale tan to gray, sometimes with iron staining
Reported at these sites
About the category
Shell fossils, ammonites, echinoids, corals, and bryozoans. Often preserved as molds, casts, or replaced minerals rather than original shell.