TAPHONOMY OF MULTIPLE BONEBEDS IN THE ROUND MOUNTAIN SILT, KERN COUNTY, CALIFORNIA: EVIDENCE FROM STRATIGRAPHY AND A UNIQUE WHALE SKULL

The newly discovered Eagle Crest bonebed, uncovered by paleontological mitigation of a housing development, contains a concentration of marine fossils in the lower Round Mountain Silt, stratigraphically below the famous Sharktooth Hill bonebed. Comparisons of the two bone beds in the Round Mountain Silt reveal significant differences in composition and preservation. The Eagle Crest bonebed produced 90 taxa, including plants, mollusks, echinoderms, crustaceans, fish, sharks, a sea turtle, marine mammals, and a horse. A small skull of a mysticete cetacean provides evidence for similarities and dissimilarities between the bonebeds. It is obscured by a sedimentary shroud, perhaps formed by a bacterial mat or inorganic precipitation of manganese and iron. In order to preserve the shroud, a CT-scan at the USC Molecular Imaging Center was used to view the fossil. The scan revealed a complete mysticete skull, although it is one of the smallest baleen whale skulls yet known, at only 56 cm in length. The encrustation of the skull and articulated mandibles suggest that it was exposed to seawater for an extended period of time on the sea floor but not to strong currents before burial, indicating a hiatus in deposition that promoted bonebed accumulation. The lower density of bone and higher proportion of articulated skeletons in the Eagle Crest bonebed suggest that it differs from the better-studied Sharktooth Hill bonebed, although similarities include encrusted and degraded bones and terrestrial species. It probably represents a shorter interval of time and a less vigorous current regime over this time.