San Diego Natural History Museum--Your Nature Connection[BRCC San Diego Natural History Museum: Paleontology]
Pliocene Era Whale Uncovered
Otay Ranch: February 16, 2000

A 4 million-year-old fossil skull and partial vertebrae of an extinct species of baleen whale, Balaenoptera davidsoni, were uncovered on February 16 by Pat Sena, a paleontologist at the San Diego Natural History Museum. The fossil was discovered on the Village 1 West project site at Otay Ranch, a new planned community being developed in southern Chula Vista by the Otay Ranch Company. The whale lived during the Pliocene Epoch and was a "teenager" when it died—the cranial bones hadn't completely fused. Although the skull preserves markings left by a feeding shark, it is impossible to determine whether the feeding was related to predation or scavenging. The whale carcass eventually sank to the bottom of the shallow sea and was covered by layers of sediment washed down from the mountains and adjacent sea cliffs. Later, the sea floor was uplifted more than 500 feet, and over the eons the sediment compacted into sandstone.

The fossil whale was collected by the Museum’s field paleontology staff using traditional field techniques developed for collecting large vertebrate fossils such as dinosaurs and large mammals. The partially exposed specimen was covered with a plaster "jacket" constructed with strips of burlap soaked in plaster-of-Paris and reinforced with steel pipes. The jacket was then turned over and a cap of plaster-soaked burlap applied for additional support. Three jackets were thus constructed ­ one containing the skull, a second containing portions of the rib cage and thoracic region of the spine, and a third containing portions of the lumbar region of the spine.

Museum preparator and cast-maker Fritz Clark carefully cleans the baleen whale fossil skull. Fritz sits to the right on a crate; the partial skull rests on a large pallet, covering nearly the entire surface.
Museum preparator and cast-maker Fritz Clark carefully cleans the skull.

After being transported to the Museum, the specimen is now being prepared by staff preparator Fritz Clark. Preparation involves the use of knives, dental picks and brushes to uncover the fossil and special hardeners and glues to stabilize the fragile cranial bones.

Although the Museum has another skull of this fossil species, the Otay Ranch skull is more complete and preserves previously unknown portions of the rostrum and braincase. The new find will allow scientists to more fully describe this extinct baleen whale and understand its evolutionary relationship to other fossil, as well as, living baleen whales. Any decision about exhibiting the fossil whale won't be made until after the Museum expansion is completed.

Updated by Dr. Tom Deméré, April 2000