More than 500 specimens believed to be about 20 million years old have been unearthed in Fremont.

The fossils include teeth from the biggest prehistoric shark and what appears to be an entire whale skeleton. The specimens were uncovered during construction for the Calaveras Dam Replacement project.

The new dam is being built next to the existing Calaveras Dam. Officials said 20 million years ago the ocean extended inland as far as the Central Valley, which is why fossils are being discovered in the area.

The prehistoric specimens were found during construction of the new dam, which calls for 10 million cubic yards of rock, soil and dirt to be moved.

"We've found both vertebrates and invertebrates," said San Francisco Public Utilities Commission spokeswoman Betsy Rhodes.

Among the invertebrates founds are snails, scallops the size of dinner plates and barnacles, Rhodes said. Vertebrates unearthed include whale skulls and shark teeth.

Paleontologists at the Calavares Dam Replacement project have also found the teeth of an animal called the Desmostylus, a long extinct hippo-like creature.

More resources and a team of paleontologists have been called to the area to protect, extract and identify the fossils.