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Geologic Timeline: The last 144 million years of Earth's 4.6 billion year history.
Crassatellid clam
SDNHM catalog no. 20829.
Crassatellid clam fossil. This specimen measures approximately 4.25 inches (11 cm) long.


Crassatella uvasana
Crassatellid clam


In Our Region
Shells of C. uvasana have been collected from Eocene-age siltstones in San Diego, Del Mar, Encinitas, Carlsbad, and Leucadia in San Diego County.

Crassatella uvasana is an extinct species of large crassatellid clam. Clams are bivalve mollusks; their shells are made up of two valves (shell halves). The shell may be either triangular, trapezoidal, or rounded in shape, and either smooth or covered with concentric markings that radiate from the hinge. Two or three teeth are typically found on the hinge plate, inside the shell.

These crassatellid clams were common in warm, shallow seas where they burrowed into the sandy substrate for shelter.

Pleistocene Epoch 1.8 million-10,000 years ago.
Pliocene Epoch 5-1.8 million years ago.
Miocene Epoch 24-5 million years ago.
Oligocene Epoch 34-24 million years ago.
Eocene Epoch 53-34 million years ago.
Paleocene Epoch 65-55 million years ago.
Cretaceous/Tertiary Boundary Rock, 65 million years ago.
Cretaceous Period 144-65 million years ago.
Earth's history began 4.6 billion years ago.
MYA = million years ago.