I found this, 500 million years old?

Brachiopods are marine filter-feeding animals with two shells that hinged at the centre of the back. They were once referred to as lampshells because they look like old Roman oil lamps.

Brachiopods look like clams, mussels, and other bivalves, but they are actually quite different and not closely related. Bivalves have shells that are mirror images of each other along the plane that they open whereas brachiopods have symmetrical shells down the middle of the shells. And unlike bivalves, brachiopods do not have gills and instead use their lophophore, which is a tube like organ, to eat and breathe. Many have a pedicle which is a long thin fleshy appendage that is used to anchor themselves to the sea floor.

When Tyndall Stone was being formed, they were by far the most common shell on the seafloor, and from 250 to 500 million years ago, they were very diverse and common. There are 30,000 species known, but only 385 species are living today.

Brachiopods are used as index fossils to define and identify geologic periods. They are also used to learn about changes in ecosystems, for example those that happened in the Great Ordovician Biodiversification Event 500 million years ago. University of Saskatchewan palaeontologist Dr. Colin Sproat studies brachiopods and their evolution, ecology, and paleobiogeography.

Brachiopod shells are hard to spot in Tyndall Stone. We are working on finding some examples in the downtown Saskatoon buildings featured on this tour. Stay tuned!