Belemnitella americana (Morton)
|Description: These bullet-shaped objects come to a blunt to tapered point on one end. The other end is somewhat fluted with a conical shaped opening which in life held the part of the shell that contained most of the animal. The cross section of the guard is oval to circular and they always have a crack down its length. Mostly they are broken in half separating the front end from the rear. Most of these guards are amber in color but can be yellowish-orange to brownish-orange. In life these guards were covered with a network of veins that ran underneath the skin. In unworn specimens the impressions of this network can clearly be seen. On the bottom, there is usually a groove that runs the length of the conical shaped opening. Most Belemnitella guards are between 4 to 9 cm (about 1.5 to 3.5 in) long but some can get as large as 12 cm (about 4.75 in) long. They have a diameter between 4 mm to 2 cm (about .2 to .75 in). These guards may have drill holes from the sponge Cliona cretacica.
Sometimes the sediment that filled this opening is preserved as an internal mold.
Commonality: Belemnitella is the most common cephalopod at Big Brook. They can be found anywhere in the Navesink formation but they mostly occur in moderate numbers in a layer about 1.3 meters (about 4 feet) from the stream surface just down stream from the Boundary Road bridge. In freshly worn formation bank surfaces, they can sometimes be seen protruding from the clay. There are also some concentrations just at the Mt. Laurel / Navesink boundary. They can on occasion be found as molds in the Mt. Laurel.
Similar fossils: There are no fossils that can be confused with Belemnitella. Some concretions can look similar, but the lack of a regular form and the rust brown to orange color should serve to differentiate them from belemnites.
Size: These "squids" were in life between 5 to 15 cm (about 2 to 6 in) from the tip of the shell to the tentacles.
Notes: The local people refer to them as "bullets" and indeed this is an accurate description of their shape. These objects formed the guard, or rostrum, that helped the "squid" to keep stiff while swimming backwards.
These "squids" might have formed, as their modern counterparts do today, small to large schools. They were in sufficient numbers that they might have been one of the food items for mosasaurs, plesiosaurs, the gavil-like "crocodile", and sea turtles. If this is true, then the indigestible guards must have given these large marine reptiles with a good case of indigestion.
Although Belemnitella looked like a modern type "squid", it is more closely related to the cuttlefish, hence "squid" is in quotes. Belemnitella americana is the index fossil for the Matawan Group.
|Rostrum or guard|
Bellemnitella in matrix
|Size range for Belemnitella|