Before the techies, yuppies, hippies and yippies, the San Francisco Bay Area was still a place of vibrant diversity and cutthroat competition. Right here, near the Caldecott Tunnel, the Aeulorodon, a huge hyena-like dog, chased and devoured the Hipparion, a pony-sized early horse. Nearby, a lionlike bear (Barbourofelis) and a wild pig (Prosthenops) and a pond turtle (Clemmys) found their own ways to exist.
We know all this because of fossil deposits from the Miocene era (between 23 and 5 million years ago) in Orinda, Moraga, and Blackhawk. This was the peak of mammalian diversity, and had a quite different climate, with year-round rain rather than the Mediterranean climate we enjoy today. Dr. Mark Goodwin, of UC Berkeley’s Museum of Paleontology, described Miocene relics while passing around 10 million-year-old rhinoceros and horse bones to the guests at June’s enrichment lecture.
Our nearby deposits range from the edge of Oakland to Orinda, and come from stream deposits (shale rock), the residue of a former deep marine basin (chert rock and shale) and volcanic deposits (sandstone and igneous rocks). We find fossils from the benthic (deep water) areas, as one-celled organisms called diatoms recrystallize in the sediment, and other tiny animals known as foraminifera secrete a silica formation. We also find the shells of bivalves, gastropods and arthropods.
As for land creatures, we find camel, horse and rhinoceros bones, and remnants of bay laurel trees. Camels and horses actually evolved in North America, we have discovered, and nearly died out before being reintroduced by the Spanish.
At the Blackhawk Ranch Quarry, near Mt. Diablo, there are some uplifted rocks that date back 75 million years. Within those rocks we see evidence of past sycamore, elm, poplar, and willow trees, and bones and fossils from horses, camels, saber-toothed cats, beavers, and the large hyena-like dogs.
Dr. Goodwin showed lots of photos of paleontologists at work throughout the entire process of excavation and fossil extraction and preparation. He pointed out that fossil preparation, that is, getting the artifact ready for exhibition, is a unique career field for which there is no academic training available, but only an apprenticeship with someone who currently holds that position at a museum.
Fossilization occurred rather quickly in the specimens we have found from the Bay Area. It happened fast enough that when researchers dissolve the bones in acid, they find the remains of soft tissues that look like blood vessels.
We can estimate the age of organic material by measuring the level of certain isotopic variations on the number of neutrons, as the atoms with extra neutrons lose them over time. Also, researchers can track pH, temperature and salinity changes over the years.
We have not yet found dinosaur remains, but that does not necessarily mean that these large reptiles did not live in the Bay Area. We lack the freshwater deposits from the Cretaceous period that would likely contain any existing dinosaur remains.
UC Berkeley’s Museum of Paleontology contains models of dinosaur bones, and several dinosaur species did roam North America. Dr. Goodwin closed his talk by inviting everyone to visit this museum during Cal Day, a Saturday in April when the it is open to the public.