A comprehensive approach using palaeontology, petrography, stable isotope geochemistry and biomarker analyses was applied to the study of seven small methane-seep carbonate deposits. These deposits are in the Oligocene part of the Lincoln Creek Formation, exposed along the Canyon and Satsop Rivers in western Washington. Each deposit preserves invertebrate fossils, many representing typical seep biota. Authigenic carbonates with d 13 C values as low as )51& PDB reveal that the carbon is predominately methane derived. Carbonates contain the irregular isoprenoid hydrocarbons 2,6,11,15tetramethylhexadecane (crocetane) and 2,6,10,15,19-pentamethylicosane (PMI), lipid biomarkers diagnostic for archaea. These lipids are strongly depleted in 13 C (d 13 C values as low as )120& PDB), indicating that archaea were involved in the anaerobic oxidation of methane. Small filaments preserved in the carbonate may represent methanotrophic archaea. Archaeal methanogenesis induced the formation of a late diagenetic phase, brownish calcite, consisting of dumbbell-shaped crystal aggregates that exhibit d 13 C values as high as +7& PDB. Clotted microfabrics of primary origin point to microbial mediation of carbonate precipitation. Downward-directed carbonate aggregation in the seeps produced inverted stromatactoid cavities. Large filaments, interpreted as green algae based on their size, shape, arrangement and biomarkers, imply that deposition occurred, in places, in water no deeper than 210 m.

Osedax is a recently discovered group of siboglinid annelids that consume bones on the seafloor and whose evolutionary origins have been linked with Cretaceous marine reptiles or to the postCretaceous rise of whales. Here we present whale bones from early Oligocene bathyal sediments exposed in Washington State, which show traces similar to those made by Osedax today. The geologic age of these trace fossils (∼30 million years) coincides with the first major radiation of whales, consistent with the hypothesis of an evolutionary link between Osedax and its main food source, although older fossils should certainly be studied. Osedax has been destroying bones for most of the evolutionary history of whales and the possible significance of this "Osedax effect" in relation to the quality and quantity of their fossils is only now recognized.annelids | deep sea | fossil record | symbiosis T he deep sea has the least explored biodiversity (1, 2), and the scarcity of food in the abyss has resulted in a range of evolutionary novelties (3)(4)(5). A recent discovery in this field is the annelid genus Osedax that lives and feeds exclusively on bones on the seafloor (6). Age estimates using molecular clocks suggest either an Eocene to Oligocene origin of Osedax, coincident with the rise of whales (6, 7), or a Cretaceous origin (7), depending on the rate used, but these estimates have not yet been corroborated by fossil evidence. Osedax belongs to the family Siboglinidae that includes the large tube worms living around deep-sea hydrothermal vents and cold seeps (6). Whereas other siboglinids live in symbiosis with chemoautotrophic bacteria, Osedax has symbionts that are heterotrophic γ-proteobacteria consuming mainly collagen and/or lipids (8). The symbionts are housed mainly in tissue that forms a "root system" extending into the bone. The action of the roots and associated bacteria results in the destruction of the bone interior. The roots are connected to the main body of the worm that emerges from the bone via a circular hole on the bone surface (6, 9). Such holes and excavations in fossil bones can arguably be used to infer the presence of Osedax in the geologic past. Here we report Oligocene whale bones that show such traces. ResultsTraces resembling those left by Osedax in whale bones today were found in two early Oligocene whales from bathyal sediments of the Pysht Formation in northwestern Washington State (Fig. 1). The whale fossils were preserved within hard carbonate concretions from rock outcrops on the modern beach terrace. The whales were small, toothed mysticetes with a body length estimated to not exceed 4 m. One specimen (USNM 539939) is the posterodorsal part of a skull that includes a right dentary, a periotic, a bulla, some teeth, and other fragments in addition to six small shark teeth (?Somniosus sp.). Boreholes are on the lateral surface of the dentary and on two rib fragments ( Fig. 1 A and C). Some of the bones preserve marks left by the teeth of scavenging sharks. The ventral portion of the skull was co...

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