Fossil Sirenians, Related to Today's Manatees, Give Scientists New Look at Ancient Climate
ScienceDaily (Apr. 24, 2011) — What tales they tell of their former lives, these old bones of sirenians, relatives of today's dugongs and manatees. And now, geologists have found, they tell of the waters in which they swam.
A fossil sirenian named Halitherium schinzi, shown at the Paris National Museum of Natural History. (Credit: Mark Clementz)
While researching the evolutionary ecology of ancient sirenians -- commonly known as sea cows -- scientist Mark Clementz and colleagues unexpectedly stumbled across data that could change the view of climate during the Eocene Epoch, some 50 million years ago.
Clementz, from the University of Wyoming, published the results in a paper in this week's issue of the journal Science.
He and co-author Jacob Sewall of Kutztown University in Pennsylvania used their findings to dispute a popular scientific assumption about the temperature and composition of seawater during the time marked by the emergence of the first modern mammals.
The Sirenia, named for the sirens or mermaids of Greek myth, is an order of aquatic, plant-eating mammals that live in swamps, rivers, estuaries, marine wetlands and coastal waters.
Four species of "sea cows" are alive today, in two families and genera: the dugong, with one species, and manatees with three species.
Sirenia also includes the Steller's sea cow, extinct since the 18th century, and others known only from fossil remains. The order evolved during the Eocene more than 50 million years ago....
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Science 22 April 2011: Vol. 332 no. 6028 pp. 455-458 DOI: 10.1126/science.1201182REPORT
Latitudinal Gradients in Greenhouse Seawater δ18O: Evidence from Eocene Sirenian Tooth Enamel
Mark T. Clementz1,2,* and Jacob O. Sewall3,*
Author Affiliations
1Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA.2Program in Ecology, University of Wyoming, Laramie, WY 82071, USA.3Department of Physical Sciences, Kutztown University, Kutztown, PA 19530, USA.
*To whom correspondence should be addressed. E-mail: mclemen1@uwyo.edu; sewall@kutztown.edu
ABSTRACT
The Eocene greenhouse climate state has been linked to a more vigorous hydrologic cycle at mid- and high latitudes; similar information on precipitation levels at low latitudes is, however, limited. Oxygen isotopic fluxes track moisture fluxes and, thus, the δ18O values of ocean surface waters can provide insight into hydrologic cycle changes. The offset between tropical δ18O values from sampled Eocene sirenian tooth enamel and modern surface waters is greater than the expected 1.0 per mil increase due to increased continental ice volume. This increased offset could result from suppression of surface-water δ18O values by a tropical, annual moisture balance substantially wetter than that of today. Results from an atmospheric general circulation model support this interpretation and suggest that Eocene low latitudes were extremely wet.
Received for publication 2 December 2010.Accepted for publication 4 March 2011.
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