The large fossilized skeleton of a whale was uncovered Thursday on the zoo's grounds by an excavating machine digging a hole for a storm-water runoff tank, the Los Angeles Times reported.
The excavation work was stopped in accordance with state law as paleontologists from a nearby museum quickly assembled.
By Friday, museum personnel were carefully chipping, dusting and digging in preparation for the skeleton to be encased in plaster and taken back to the museum for additional study.
Paleontologists had expected digging at the site just inside the zoo fence would uncover some shells, and maybe some shark teeth.
But finding a 20-foot, largely intact whale fossil was unexpected, they said.
The whale fossil is proof that despite the civic self-image of San Diego as a place where everything is new, the truth is somewhat different.
"The people are new," Sarah Siren, the museum's paleontology field manager on site, said. "The whales have been here the whole time."