Parapuzosia bradyi is a gigantic species of ammonite, reaching diameters of more than 4.5 ft (1.4 m) by 6 ft (1.8 m).

It is the largest species of ammonite in North America.

It had a moderately involute shell with flat sides.

The inner whorls are slightly oval-shaped with prominent ribbing.

They are only known from the upper layers of the Eagle Sandstone and Cody Shale formations (both Late Cretaceous).