Baculites compressus
Pierre Formation
Upper Cretaceous (Campanian)
Pennington County, South Dakota

Here is seen a remarkable display specimen of Baculites. Perched on its original concretion matrix are two Baculites with beautiful iridescent shell. Each Baculite anterior is as originally found but the posterior sections are composite. Both Baculites show the aperture. This example is a dramatic display specimen. The longer Baculites is 22 inches and the shorter is 20 inches.

Baculites compressus is the most abundant ammonite in the middle Pierre Shale in South Dakota. It is easy to identify because of its very compressed elliptical cross section and smooth to weakly ribbed venter. Large specimens have slight undulations on the flank. The shell tapers rapidly and can curve slightly in juveniles. It is almost straight in adults. B. compressus has a very complex suture pattern.