Snail

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.

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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 snail (Echphora gardnerae ) from Calvert Cliffs, Maryland
Photo by Mary Parrish, Smithsonian, National Museum of Natural History

About Gastropods (Class Gastropoda): Paleobiology

During their long history on Earth (about 500 million years), gastropods have evolved various ways to feed. Flat snails (e.g., Maclurites) likely lived like clams, sitting in one place and eating small food suspended in the water. They were common in the Paleozoic, but are now extremely rare. Most gastropods actively find detritus or algae to eat, scraping food off rocks or other surfaces using a special mouthpart (the radula). Other gastropods are carnivores: shells with holes in them are evidence of gastropods using their radula to drill a hole and eat the animal inside. The earliest gastropods were detritivores, but carnivory has evolved independently several times (convergent evolution). During the shift from herbivory to carnivory, the teeth on gastropod's radulas were lost or modified for use as predatory tools. Early gastropods lived in the sea, but by the Carboniferous (360 - 299 million years ago) some freshwater gastropods invaded land. During the transition to land, gastropod shells either remained rather thick (in dry climates) or were reduced or even lost altogether (in humid climates).

Slab of fossil, shelled animals called ammonites, now extinct on Earth
Photo by Chip Clark, Smithsonian, National Museum of Natural History

About Mollusks (Phylum Mollusca): Paleobiology

Mollusks have inhabited the Earth for at least 540 million years, dating back to the early Cambrian period. The fossil record of mollusks consists mostly of shells. Rarely, it includes mouthparts (radulas) or the trapdoors (opercula) that cover shell openings. The rest of the body is soft and usually does not fossilize. Before the Cambrian, taxa such as Kimberella had many traits expected of early molluscs, but no shells or spines. Cambrian, worm-like animals with spiny scales, such as Wiwaxia, had mollusk-like mouthparts. The earliest agreed-upon mollusk looked like a snail with a single, cap-like shell that curved at the tip. More than 90,000 living species of mollusk have been described, plus another 70,000 species known only from fossils. Because many mollusks live in remote places such as in the bottom sediments of deep ocean, and new species are being discovered at a rapid rate, scientists think that many more species remain to be described.