Meet Pseudothurmannia — one of those marvellous Cretaceous ammonites that looks as though nature spent extra time on the details.
This extinct cephalopod belongs to the subclass Ammonoidea and is tucked neatly within the family Crioceratitidae, part of the wonderfully curly branch of ammonites known as the Ancylocerataceae.
A proper pedigree, if ever there was one.
Now, have a look at those shell lines — the intricate, looping seams known as sutures. These are no random squiggles.
They are the biological fingerprints of ammonites, each species carrying its own signature pattern. To the trained eye, they tell time as neatly as any watchmaker.
Compare the sutures of this beauty with its kin, and we know Pseudothurmannia cruised ancient seas during the Early Cretaceous, from the Hauterivian through to the Barremian, some 132 to 125 million years ago.
Like its modern cousins — squid, cuttlefish and octopus — this fellow was no passive floater. Hidden within that elegant shell was a sharp, beak-like jaw surrounded by a ring of grasping tentacles. Those arms were built for business, used to seize prey from the water column: plankton, small fish, crustaceans and whatever else wandered too close.
And catching a fish while swimming is no easy business. Try it yourself and report back. Ammonites, however, were masters of the ambush — swift, buoyant, and gloriously well-equipped for life in the open sea.
For millions of years, they were among the great success stories of the oceans… until, of course, the curtain came down at the end of the Cretaceous.
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.
