Cymatoceras sp.: This is a nautiloid belonging to the genus Cymatoceras, discovered in Ambatalafia, Mahajanga Province, Madagascar.
These nautiloids, much rarer than the commonly seen ammonites, belong to the extinct genus from the nautilitacean cephalopod family, Cymatoceratidae. They thrived from the Late Jurassic to Late Oligocene, approximately spanning from 155 to 23 million years ago. In this particular case, they date back to around +/- 90 million years ago. The shell of a Nautilus consists of two layers. The inner layer displays an iridescent shine, while the outer layer provides protection against external forces. Within the shell are septa, which partition the living area of the shell into compartments, aiding the animal in maintaining balance and position in the water column. Nautiloids like Cymatoceras are considered 'living fossils,' as similar species still exist in our oceans.