FOSSIL AND LIVING BIVALVES
Over 100 million years ago North Texas was located under a warm, shallow subtropical sea. Some of the most prominent sea creatures in this region were the marine bivalves–mollusks with 2 shells (valves) like mussels, oysters, and clams. This exhibit case illustrates the great diversity of bivalves that existed here during the Early Cretaceous (around 95 to 110 million years ago) and their living relatives. The organization of the tree indicates relationships and each shelf represents a particular family of bivalves. The joint from which lines diverge to different shelves indicates how closely related families are to one another. For example, pen shells (Pinnidae) are more closely related to winged oysters (Pteriidae) than either is to river mussels and naiads (Unionidae).