Big Brook Fossils


Big Brook is a small stream that cuts into the Navesink Formation in northern New Jersey. It is late in the Cretaceous, just a little later that the fossils from the Pierre Formation at Rocky Ridge but the fossil represent an very different group of marine animals. There was a continent between the bodies of water.


In the Big Brook stream bed, resistant fossils like shark's teeth can be sifted but the banks contain many delicate specimens that are destroyed by stream action. Since I collected there, digging in the banks has been prohibited. Here are a couple of specimens that demonstrate the abundance.

Fossil assemblage

Fossil assemblage


The most common cephalopod at Big Brook is a belemnite. Ammonite can be found but they are uncommon. The example is a specimen labeled, "baculite," in a collection. I borrowed it for a talk.

Belemnitella americana


There are several genera of oysters and many specimens have holes drilled by carnivorous snails.

The most abundant species is Pycnodonte convexa in which the valves are unequal.

The most abundant species is Pycnodonte convexa in which the valves are unequal.

Another common species, Exogyra costata, also has unequal valves.

Another common species, Exogyra costata, also has unequal valves.

Both Pycnodonte convexa and Exogyra costat have very thick shells but this didn't prevent oyster drills from attacking them. In this Exogyra, the hole the drill made is 10 mm deep.

Agerostera mesenterica is about an inch long and usually occurs as a single value. Here are views a couple of individuals in which both valves survived together.

This species was also subject to predation. In addition, here is a cast and a specimen with a pearl.

Small oyster #2

Small oyster #3

Small oyster #4. Notice the encrusting byrozoa.

A scallop. These are very difficult to collect because they are delicate. I was only able to prepare this one because it is supported by a large oyster shell.



Snails are usually only a cast. Judging from the number of drill holes, gastropods must have been abundant.

Worm shells (with encrusting bryozoa)

Worm shells


Both encrusting and branching bryozoa occur. Here are two branching species. Look at the first assemblage and other specimen for encrusting bryozoa.



Spiropora sp.

Choristothyris plicata These small brachiopod are abundant.

Brachiopods on a larger shell

Tiny pieces of echinoderms including spines are present. There is also a spine in the first assemblage.


Other New Jersey Material

Before we leave New Jersey and its Cretaceous deposits, there is a site north of Big Creek where amber occurs. Some of the oldest known insects in amber have been found here. This a tiny midge. It's about 3 mm long.

Above the layer with amber, carbonized wood, occurs.

Start in the upper left corner going clockwise, the sharks are Crow Shark, two Porbeagle Shark, and a Goblin Shark. The long tooth at the bottom is a tarpin tooth.

A broken fish vertebra