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At UCMP, while the whale skull and skeleton were being prepared, tiny fossil molluscs (clams and snails) were discovered attached to the bones. Then UCMP graduate student Nicholas Pyenson and UCMP Museum Scientist David Haasl determined that this association represented a fossilized example of a whale-fall a collection of deep-sea organisms that survives on the carcass of a dead whale that falls to the ocean floor. Pyenson and Haasl pointed to several lines of evidence. First, the rocks on Año Nuevo Island represent deep-sea sediments, pointing to an original burial nearly 1000 m below sea-level during the middle of the Miocene epoch, 11-15 million years ago. Second, both the skeleton of the whale and the position of the molluscs on it were consistent with the arrangements known from modern-day examples of whale-falls. Finally, the fossil molluscs that they identified belong only to a group of living ones that are specific to modern whale-falls, forming a unique biological community.
When whales die and fall to the sea floor in deep water, they represent a substantial food source in an otherwise deserted seafloor. The dead whale is then quickly colonized by a host of scavengers and other organisms that either eat or inhabit the carcass and its bones. During the later stages of decomposition, the whale carcass is colonized by bacteria that live off of the sulfides produced by the decomposition of proteins. Other organisms, like the molluscs found on this whale fossil, are also found in other sulfide-rich environments, such as deep-sea hydrothermal vents and methane seeps. While widely reported from the seafloor around the world, this biological community is only now being recognized in the fossil record. This specimen is the first known example from the fossil record of California, and the youngest yet documented in the world. Its discovery shows us how the evolution of whales was connected not only with events in the oceans but also on the seafloor, where their carcasses allowed for the evolution of a completely novel ecological niche.
In the collections
Pyenson, N.D., and D.M. Haasl. 2007. Miocene whale-fall from California demonstrates that cetacean size did not determine the evolution of modern whale-fall communities. Biology Letters 3(6):709–711. DOI: 10.1098/rsbl.2007.0342
Sea lions and seabirds, 1987, 2007 and bivalve photos courtesy of Dave Haasl; lone elephant seal photo by Dave Smith; two Monterey Formation photos by Carole Hickman; skull photo by Judy Scotchmoor.
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