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Vetulonaia sp. (fossil clams) (Morrison Formation, Upper Jurassic; Dinosaur National Monument, Utah, USA) 47 | by James St. John
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Vetulonaia sp. (fossil clams) (Morrison Formation, Upper Jurassic; Dinosaur National Monument, Utah, USA) 47

Vetulonaia sp. - fossil freshwater bivalves in the Jurassic of Utah, USA.

 

The ellipsoidal structures in the rock are fossil freshwater clams at Dinosaur National Monument, Utah. The host rock in this area ranges from a sandstone to pebbly sandstone to granulestone to almost a conglomerate, but the pebbles are dominantly angular to subangular in shape. Many granules and pebbles are composed of dark-colored chert. This horizon is famous for an abundance of Late Jurassic dinosaur bones from sauropods, stegosaurs, and theropods. Across the valley from here, the bed was intensely quarried starting in the early 1900s. Many dinosaur fossils ended up at Carnegie Museum in Pittsburgh, Pennsylvania, but many bones were also left in the rocks for the general public to examine and appreciate. The Carnegie Quarry itself has a structure built over it for protection from erosion. The clam and dinosaur bone-bearing outcrop seen here is outdoors.

 

The clams do not have their shells preserved - they are internal molds. Molds are a common type of fossil preservation style, consisting of impressions of the exterior or interior surfaces of hard part shells or skeletons.

 

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

 

Stratigraphy: Carnegie Quarry Sandstone, Brushy Basin Member, Morrison Formation, Kimmeridgian Stage, Upper Jurassic, ~150 to 156 Ma

 

Locality: spur trail along Fossil Discovery Trail, Dinosaur National Monument, northern Uintah County, northeastern Utah, USA

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See info. at:

en.wikipedia.org/wiki/Dinosaur_National_Monument

 

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Taken on June 9, 2012