Ark Clam

Associated Smithsonian Expert: Peter Wagner, Ph.D.

Peter Wagner (in the front) collecting snail fossils from middle Ordovician rocks in Death Valley, California

Courtesy of Shanan Peters, University of Wisconsin

Dr. Peter Wagner is a paleontologist and curator of Paleozoic mollusks at the Smithsonian National Museum of Natural History. He got his start studying geology at Michigan State University. He went on to earn a master's degree in Geological Sciences at Michigan State University, where his thesis focused on relationships among some Ordovician gastropods. As a doctoral student at the University of Chicago, Peter studied rates and trends of morphologic evolution as well as phylogenetic diversity of early gastropods. He served as a curator at the Field Museum of Natural History for more than a decade before joining the Smithsonian. His current research focuses on models of morphologic evolution, and how they affect our ideas of relationships and diversification among Paleozoic mollusks, particularly gastropods.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.
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Drawing of fossil Miocene clam (Mercenaria sp.) from Calvert Cliffs, Maryland
Photo by Mary Parrish, Smithsonian, National Museum of Natural History

About Pteriomorph Bivalves (Subclass Pteriomorphia): Paleobiology

Pteriomorphia includes many of the bivalves we know best today, such as mussels, oysters, and scallops. The first Pteriomorphia lived on Earth during the middle Ordovician (about 470 million years ago). They evolved as part of the huge diversification of bivalves that occurred during what is called the Cambrian Explosion. One of the oldest known bivalves, Fordilla trovensis, may be the ancestor of modern mussels. Various shell shapes emerged during the Cambrian Explosion, and internal body structures changed as well. One of the changes was enlargement of the gills, which are used by bivalves to get oxygen from their watery surroundings. Larger gills became useful for feeding by acting as strainers to trap food particles. Further changes eventually led to the intricate gills of modern Pteriomorphia that include a complex structure with lots of surface area for filtering and grooves for transporting food.