Echinoids have lived in the sea from about 450 million years ago, which 220 million years before dinosaurs appeared. The living represent echinoids are the familiar sea urchins.

Fossil echinoids closely resemble some living sea urchins, which helps us to understand how they lived. They have a hard shell (referred to as a test) covered with small knobs (tubercles) to which spines are attached in living echinoids. The test and spines are the parts normally found as fossils.

As the name indicates bivalvia are molluscs with two, often identical shells also called valves. The animal resides within the valves. Clams, oysters and mussels are among the nearly 15,000 species that make up this class. Over 80% of bivalves are marine and they usually live one the ocean’s bottom. Bivalves can swim, burrow or cling to surfaces. Bivalves first appeared in early Cambrian.

Ammonites were marine animals belonging to the Phylum Mollusca and the Class Cephalopoda, which includes their living relatives the octopus, squid, cuttlefish and nautilus. These creatures lived in the sea between 240-65 million year ago.

The ammonite’s shell was divided into chambers separated by walls known as septa. The septa had frilled edges, intricate lines, of varying complexity and known as sutures. 

Female ammonites grow up to 400% large than male, presumably to have more space to lay eggs.

Ammonites may have been the favourite food of the marine reptile called the Plesiosaur. As per scientific research, the ammonites became extinct along with the Dinosaurs 65 million years ago.