The University of Iowa
The University of Iowa News Services Home News Releases UI in the News Subscribe to UI News Contact Us

University of Iowa News Release

Release: April 30, 2003

(Photo: left--Otolith, click on photo for high resolution version; right--Scott Carpenter)

Researchers Link Life Of Ancient Fish, Ancient Earth

In the May 1 issue of the journal Nature, a University of Iowa researcher reports using fossilized fish ear stones (otoliths) to reconstruct the life history of an ancient fish and provide temperature estimates for the time period just prior to the Cretaceous-Tertiary (K-T) Boundary about 65 million years ago. Some scientists have speculated that a large asteroid struck the Earth about that time, altering the climate and causing the extinction of dinosaurs and other life forms.

 

Scott J. Carpenter, research scientist in the UI Center for Global and Regional Environmental Research (CGRER), associate director of the Paul H. Nelson Stable Isotope Laboratory, and adjunct associate professor in the College of Liberal Arts and Sciences department of geoscience, says that his work provides another piece of the paleo-climate puzzle for the time period just prior to the end of the Cretaceous.

"This is the first published report of the life history of a Mesozoic age fish," Carpenter says. "This fish was thought to have lived in freshwater, but our analyses indicate that it never lived in freshwater."

Carpenter's study, "Migration of a Late Cretaceous fish," examined the otoliths, or ear stones, of a prehistoric fish species (Vorhisia vulpes) for which there are no known skeletons - just otoliths. He analyzed the otoliths (which grow concentrically like tree-rings), collected from the Fox Hills Formation of South Dakota, for carbon, oxygen and strontium isotope ratios. These analyses determined that the fish spawned in brackish water, migrated during the first year to open ocean waters where they remained for three years, before returning to their estuary to spawn and die. The oxygen isotopic ratios from the marine growth phase yielded a seawater temperature of about 18 degrees Centigrade (64 degrees Fahrenheit), consistent with the high temperatures during the greenhouse world of the Late Cretaceous just prior to the K-T boundary.

Carpenter says that his current research is part of an ongoing collaboration with several scientists to characterize the ecology and climate of North and South Dakota near the K-T Boundary. "The preservation of fossils in the sediments from this area is unparalleled," he says. "Clam shells look like those collected on a beach today. This preservation is why these specimens can provide such detailed geochemical information." Carpenter is currently studying freshwater clams from this region to estimate the nature of the ancestral Rocky Mountains of Wyoming and Montana -- to examine their elevation and the existence of glaciers in these mountains.

Carpenter's study, "Migration of a Late Cretaceous fish," examined the otoliths, or ear stones, of a prehistoric fish species (Vorhisia vulpes) for which there are no known skeletons - just otoliths. He analyzed the otoliths (which grow concentrically like tree-rings), collected from the Fox Hills Formation of South Dakota, for carbon, oxygen and strontium isotope ratios. These analyses determined that the fish spawned in brackish water, migrated during the first year to open ocean waters where they remained for three years, before returning to their estuary to spawn and die. The oxygen isotopic ratios from the marine growth phase yielded a seawater temperature of about 18 degrees Centigrade (64 degrees Fahrenheit), consistent with the high temperatures during the greenhouse world of the Late Cretaceous just prior to the K-T boundary.

Carpenter says that his current research is part of an ongoing collaboration with several scientists to characterize the ecology and climate of North and South Dakota near the K-T Boundary. "The preservation of fossils in the sediments from this area is unparalleled," he says. "Clam shells look like those collected on a beach today. This preservation is why these specimens can provide such detailed geochemical information." Carpenter is currently studying freshwater clams from this region to estimate the nature of the ancestral Rocky Mountains of Wyoming and Montana to examine their elevation and the existence of glaciers in these mountains.

Carpenter, who also published in the Oct. 18, 2002 issue of Science on a 30-year history of El Niño events recorded in a Central American stalagmite, says these fossils enable him to reconstruct their life histories using geochemical analyses. In effect, the fossils serve as proxies for the rapidly changing temperature of an ancient seaway and adjacent land areas that existed more than 65 million years ago in present-day South Dakota.

Carpenter's co-authors are J. Mark Erickson, James Henry Chapin Professor of Geology and Mineralogy, department of geology, St. Lawrence University, Canton, N.Y.; and F.D. "Bud" Holland, Jr., professor emeritus, department of geology and geological engineering, University of North Dakota, Grand Forks, N.D.

Carpenter's research interests also include the study of modern Alaskan scallops to provide information that helps the state of Alaska better manage its scallop industry and to document the effects of El Niño in the Gulf of Alaska (contract with the Alaska Department of Fish and Game (ADF&G)). Carpenter, with Iowa State University researcher, Donna Surge, will soon begin a geochemical study investigating the causes of the historical decline of freshwater mussels in Iowa's Rivers.

STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite 371, Iowa City, Iowa 52242-2500.

CONTACTS: Gary Galluzzo, University of Iowa News Services 319-384-0012, gary-galluzzo@uiowa.edu.