AMMONITES

Ammonites are ancient relatives of squids and octopuses. Their ability to evolve and adapt quickly allowed them to live in very diverse marine environments. They are very valuable indicators for determining the age of rocks and correlating them in different parts of the world.  

The flysch was instrumental in understanding their extinction. In 1986 the American geologist Peter Ward published an article in the Geology journal with data from Zumaia. In it, he showed that these marine cephalopods had suddenly become extinct along with the dinosaurs 66 million years ago.

This stunning specimen is about 100 million years old and belongs to the collection of giant ammonites on display at the Mutriku Geomuseum. The collection has 150 specimens and is one of the most important cases of gigantism described internationally. 

INOCERAMIDAE

These are bivalve molluscs that lived buried in the mud of the deep sea floor. They became extinct around 70 million years ago due to a change in deep-water circulation patterns, which is perfectly captured in the Algorri flysch.

Its carapace was oval in shape and had prominent growth lines. Exceptional shells measuring more than a metre in diameter have been found in some places.