Ammonites have intricate and complex patterns on their shells called sutures. The suture patterns differ across species and tell us what time period the ammonite is from.
We can see from the suture patterns shown here and by comparing it to others that are similar that this fast-moving nektonic carnivore lived in the Cretaceous, from the Hauterivian to the Barremian.
Like other cephalopods, ammonites had sharp, beak-like jaws inside a ring of squid-like tentacles that extended from their shells. They used these tentacles to snare prey — plankton, vegetation, fish and crustaceans — similar to the way a squid or octopus hunt today.
Catching a fish with your hands is no easy feat, as I'm sure you know. Ammonites were skilled and successful hunters. They caught their prey while swimming and floating in the water column.
Within their shells, they had a number of chambers, called septa, filled with gas or fluid that were interconnected by a wee air tube. By pushing air in or out, they were able to control their buoyancy in the water column. They lived in the last chamber of their shells, continuously building new shell material as they grew. As each new chamber was added, the squid-like body of the ammonite would move down to occupy the final outside chamber.
Shells of Pseudothurmannia can reach a diameter of about 4–12 centimetres (1.6–4.7 in). They show flat or slightly convex sides, with dense ribs and a subquadrate whorl section.
We find fossils of Pseudothurmannia in Cretaceous outcrops in Antarctica, Czechoslovakia, France, Hungary, Italy, Japan, Morocco, Spain, Russia and the United States. The specimen you see here is in the collection of the deeply awesome Manuel Peña Nieto from Córdoba, Spain and is from the Lower Cretaceous of Mallorca.