What is "pachydiscidae"

Pachydiscidae comprise a family of middle and upper Cretaceous ammonites (order Ammonitida) which makes up part of the Desmocerataceae.

Pachydiscidae are of moderate to large size, evolute to rather involute, and vary in section from inflated and depressed to high-whorled and compressed. They are distinguished from the Desmoceratidae by strong ribbing at some growth stage, that normally crosses the venter uninterrupted, and by the tendency to develop strong tuberculation, at least on the umbilical shoulder.

The Pachydischidae are derived from the Desmoceratidea, in the upper Albian, about the same time as the Kossmaticeratidae, but extend further into the Maastrichtian, virtually to the end of the Cretaceous.