Picture of aragonite ammonite shell fossil of a Sphenodiscus sp . The creature existed the late Cretaceous Period Upper Maastrichtian st...

The original aragonite internal shell dissolved and was replaced by opal in these belemnite fossils. They existed the Cretaceous Period. ...

Picture is of a Benthosuchus sushkini amphibian skull fossil. It dates to the Triassic Period. Fossil found in Scharzhenga River of Vachn...