This is a classic Late Jurassic ammonite fossil from Madagascar. Species is Perisphinctes sp. It's in nice shape and still has much of the white shell remaining unlike many that are just preserved as internal casts. Ammonites are an extinct group of marine invertebrate animals which died out at the end of the Cretaceous period. These mollusks are more closely related to living coleoids (i.e. octopuses, squid, and cuttlefish) than they are to shelled nautiloids such as the living Nautilus species. This specimen dates back to the Late Jurassic approximately 160 Million Years ago.

This was found near Near Sakaraha, Madagascar. This specimen measures 7.82 cm Slightly polished, this specimen has a light sheen and shows some internal sutures of the ammonite shell on one side.

The oak leaf patterns are the internal structures of the ammonite that makes these shells has structural integrity. If not, these ammonites would've have been able to withstand the tremendous bite force of mosasaurs(large marine reptiles) which hunted them back in the day. There are fossils that show that these ammonites could survive those attacks, though rarely.