Sterosternum and the giant Stromatolites
Irati Formation, Brazil, around 280 millions of years ago. Stereosternum tumidum is one of the three species of Mesosauridae. These animals were the first tetrapods to become secondarily aquatic, at the beginning of the Permian period. They inhabited the shallow waters of Whitehill-Irati Sea (or Mesosaur Sea), where giant stromatolites, up to three meters wide, existed.
