Anomoeodus phaseolus tooth from the Navesink formation

Anomoeodus phaseolus was a species of Pycnodontid fish (shell crushers which lived during the late Cretaceous. It is somewhat common within the sediments of the Navesink formation (Maastrichtian stage) and is easily found in the brooks and creeks of Monmouth County, NJ. The specimen below was found in the Ramanessin creek near Holmdel, NJ.

The top or grinding surface

Side view

Underside, note the hollow nature of the tooth.

Profile

Anomoeodus replaced their teeth much like sharks do with old, worn ones falling out and replacements growing in. This would explain their common nature and often worn look. They typically preyed on invertebrates like shrimp, crabs and oysters. They possibly nibbled at epifauna on the surface of oysters and other hard sea floor surfaces as well.
Check out more pics and info at Oceans of Kansas which has many other species of Pycnodontid fishes.

The website Fossils of NJ has a nice page of specimens found in Monmouth County, NJ