Fossils Reveal Long-Term Ecosystem Stability, Decline of Sharks

Ancient fish teeth and scales preserved in deep-sea mud showed an 85 million-year decline in shark populations, with a sudden drop to “modern” levels nearly 20 million years ago. Scripps Institution of Oceanography at UC San Diego graduate student Elizabeth Sibert will discuss these new findings during a presentation  (PP31E-08 • Wednesday, Dec. 16, 9:45 a.m. • Moscone West 2010) at the American Geophysical Union (AGU) 2015 Fall Meeting.

Sibert will present an analysis of fossil fish teeth and shark scales, called ichthyoliths, from sediment cores taken from the North Pacific and South Pacific Ocean gyres that showed the ratio of sharks and fishes have undergone major changes over the past 85 million years. The study found that the ratio of sharks and fishes was stable for tens of millions of years before being reset 66 million years ago during the Cretaceous-Paleogene mass extinction event, and again nearly 20 million years ago to modern day levels. Neither of these shifts was marked by a major climate change event despite many that happen in the intervals between these periods.

“Our results showed that climate change doesn't seem to be a major driver for restructuring the ecosystem, it just changes how much the ecosystem ‘makes,’” said Sibert.

PRESENTATION: PP31E-08 • Wednesday, Dec. 16, 9:45 a.m. Moscone West 2010 “85 MILLION YEARS OF PELAGIC ECOSYSTEM EVOLUTION: PACIFIC OCEAN DEEP-SEA ICHTHYOLITH RECORDS REVEAL FISH COMMUNITY DYNAMICS AND A LONG-TERM DECLINE IN SHARKS”