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Geologic Timeline: The last 144 million years of Earth's 4.6 billion year history.
Fossil scallop.
SDNHM catalog no. 57214.
Scallop fossil.
This specimen measures approximately 6.5 inches (16.6 cm). It was collected in 1995 during construction of the Malcolm X Library in East San Diego.

FOSSIL FIELD GUIDE

Patinopecten healeyi
Scallop
Pectinidae

Time
Pliocene Epoch

In Our Region
Shells of P. healeyi were first discovered in Pliocene-age sandstones in the Pacific Beach, Mission Hills, and Encanto communities of San Diego, and in National City and Chula Vista, California, as well as Tijuana, Baja California.

During the 1999 expansion of the Museum, specimens were found in the strata known as the San Diego Formation.

Description
Patinopecten healeyi is an extinct species of large deep-water scallop. Scallops are bivalve mollusks; their shells are made up of two valves (shell halves). In this species, the two valves are nearly flat, with 17 to 21 ribs radiating out from the hinge. This warm water species is distinguished by grooves on the ribs of the right valve, and by inter-ribs that are almost invariably found on the left valve.

P. healeyi is an important index fossil in Southern California because it became extinct suddenly with the first wave of cold temperatures that occurred during the late Pliocene Epoch. It was succeeded by another species, Patinopecten caurinus.

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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.