The rudist bivalves were an unusual reef building group common in Cretaceous tropical seas. The "elevator type" rudists looked kind of like trash cans with one cone-shaped valve stuck in the sediment and the other serving as a lid. Other "reclining" forms looked kind of like croissants resting on the bottom. Sadly, not much is known about the lifestyle of these unusual clams as they went extinct in the same event that wiped out the dinosaurs. #clamfacts
