This ribbed shell is a fossil of the order Rhynchonellida.
These brachiopods have existed since the Ordovician period 485 million years ago. Their population was severely diminished during the Permian–Triassic extinction event 252 million years ago, but Rhynchonellida became the most abundant brachiopod group during the Mesozoic.
This group is identifiable by their deep ribbed surfaces and short hinges, which usually come to a point. These bivalves were the first to evolve teeth sockets, which help to align the two halves as they close and make it harder for a predator to open the shell by twisting the valves.
It is hypothesized that the radiating ribbed pattern helps regulate the flow of water in and out of the shell.
This fossil is millions of years old, but this order still exists today, albeit not nearly as abundant as they once were.
Age: ~70 million years (Late Cretaceous)
Size: < 10g
Please note: This listing is for one brachiopod fossil. Photos shown are representative of what you will receive, please allow for variation.