Invertebrate fossils
Ammonites
Coiled cephalopods that ruled Mesozoic seas alongside the dinosaurs and went extinct with them at the K-Pg boundary 66 million years ago. Complete specimens are rare; most NJ creek finds are fragments of the iridescent inner-shell layer or impressions of the suture pattern in chalk matrix.
How to spot it
- ▸Spiral or partial-spiral coil; ribs run perpendicular to the coil direction
- ▸Suture lines — squiggly seams between chambers — are the diagnostic feature
- ▸Often preserved as a phosphatic internal mold (steinkern) rather than shell
- ▸Iridescent mother-of-pearl flecks are common in Late Cretaceous ammonites
- ▸Fragments of a single rib or suture fold still ID to genus for a careful eye
Geological context
Discoscaphites and Pachydiscus are the genera that index Latest Cretaceous (Maastrichtian) sediments — finding them tells you the age of the gravel.
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.