File:Vetulonaia sp. (fossil clam) (Morrison Formation, Upper Jurassic; Carnegie Quarry, Dinosaur National Monument, Utah, USA) 7 (48823156911).jpg

Vetulonaia sp. - fossil freshwater bivalve from the Jurassic of Utah, USA.

This is a freshwater fossil clam from an ancient river deposit in Dinosaur National Monument, Utah. The host rock was a fluvial pebbly sandstone - almost a conglomerate in places, but the pebbles are dominantly subangular in shape. The sandstone is most famous for its abundance of Late Jurassic dinosaur bones from sauropods, stegosaurs, and theropods.

The clam does not its shell preserved - it's a mold. Molds are a common type of fossil preservation style, consisting of impressions of the exterior or interior surfaces of hard part shells or skeletons. This specimen has hints of concentric growth lines preserved. Coarse sand and granules adhere to the fossil's surface in places. The yellowish and reddish coloration is from iron oxide impurities.

From exhibit signage:

Clam fossils tell us more about the river than all the other fossils! Their great numbers show that the water flowed in the river year round, although it dried up during prolonged droughts. They also tell us that the water was usually clear, and that fish were common.

The reptiles in the river - turtles and crocodiles - are very similar to the ones we have today, 149 million years later.

Classification: Animalia, Mollusca, Bivalvia, Paleoheterodonta, Unionida, Unionidae

Stratigraphy: unspecified/undisclosed member of the Morrison Formation (probably the Carnegie Quarry Sandstone of the Brushy Basin Member), Kimmeridgian Stage, Upper Jurassic, ~150 to 156 Ma

Locality: unspecified/undisclosed site in Dinosaur National Monument (probably the Carnegie Quarry), northern Uintah County, northeastern Utah, USA

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