The Ammonoids of Mutriku: An Oceanic Heritage from 100 Million Years Ago

Professor Mikel A. Lopez Horgue, from the UPV/EHU's Department of Geology, gave this lecture as part of the Summer Course "Universities looking out to sea: sailing for ocean sustainability on the Saltillo training ship".

Ammonoids are extinct cephalopod mollusks that formed one of the most diverse groups of invertebrates we know. They were abundant in the seas of our planet from 350 million years ago to approximately 65 million years ago, becoming extinct around the same time as the well-known dinosaurs.

The ammonoid fossils in Mutriku exhibit a wide range of morphologies and exceptional size compared to other sites of the same age (Albian, Middle Cretaceous; approximately 100 million years ago). The collection kept in the Nautilus museum contains more than 60% of specimens ranging from 35 to 50 cm in size, many of them being true giants when considering the average size of the represented families. Interestingly, these fossils had gone largely unnoticed by science until Jesús Narbaez and Esperanza Azkarraga from Arrasate, driven by their love for nature and innate curiosity, rescued them from coastal erosion and donated them for scientific research and the enjoyment of all.