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Brief Description: It is a group of bivalve molluscs that used to live compacted on sea rock substratum. The compacting occurs with the attachment of the larvae on the sea bottom with the left valve, which is compacted to the rock. Hippurites or Rudistes belong to the sub-class Heterodonts. They used to live in shallow tropical seas during the Upper Jurassic and Cretaceous Period. Most Hippurites have small size. However, some big ones with size reaching 50 cm have been found in cretaceous limestone. Sometimes, they form clusters that form small reefs, like in Keratovouni of Viotia. 
Bibliography: Γεωργιάδου-Δικαιούλια, Ε., Συμεωνίδης, Ν., Θεοδώρου, Γ. (2003) Παλαιο-ντολογία (μέρος Β?), Εκδόσεις Γ. Γκελμπέση, Αθήνα.