Dactilioceras Ammonite - Positive/Negative
Origin: Yorkshire, England
170 million years old
Approx 2 inches x 2 inches
** Each piece is unique so will vary in size, shape & colour
Ammonites are an extinct group of sea dwelling snail-like animals. This group includes the extremely common fossil known as goniatites. They first appeared about 500 million years ago, in the Ordovician period and they became extinct at the end of the Cretaceous period, 50-60 million years ago possibly due to the same event that wiped out the dinosaurs. Ammonites had hard external coiled shells divided into chambers by internal divisions called septae, which can be clearly seen in fossil specimens, preserved in calcite. The animal lived in the last chamber, and air or gas was contained in the other chamber and this aided buoyancy. Ammonites had a head with a mouth surrounded by tentacles, and it also had advanced eyes. It was an active predator moving through the water using a type of jet propulsion by squirting water out of the shell.
Some ammonites reached gigantic sizes up to 2 meters in diameter. These larger specimens are generally thought to have been female, the males being notably smaller. The modern representative of the ammonites in Nautilus, which lives in the Pacific Ocean at depths ranging from 500-550 meters, and it provides much evidence about these extinct animals. They are related to the octopus and squid, all having similar jaw structures. Ammonites are extremely useful to geologists for dating rocks because they evolved rapidly and show great variety in their shells.