Here's a nifty website on the Cretaceous trigoniid bivalve, Pterotrigonia (Scabrotrigonia) thoracica, which is the State Fossil of Tennessee (USA): http://www.utm.edu/departments/artsci/ggp/geo/fossil.html The only living genus of trigoniids is Neotrigonia, found in the warm seas around Australia, and it is a very pretty shell. Lucky Australians! Australia was on the opposite side of the world when the asteroid hit Yucatan. North American molluscan faunas were hit hard. Oh, yeah, the dinosaurs went extinct then too. A list of other US State Fossils is also given. Andrew K. Rindsberg Geological Survey of Alabama