Listening to fish for extinction clues.Some species of fish that survived worldwide extinctions about 34 million years ago left behind tiny fossils that suggest that cool winters caused the die-off.Otoliths--literally, ear stones--are calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. structures in fishes' ears. These structures grow throughout the fishes' lives and lay down layers resembling tree rings. Because fish are cold-blooded, the ratio of two oxygen isotopes--oxygen-18 to oxygen-16--trapped in a layer directly reflects the temperature of the water in which the fish lived at that time. The colder the temperature, the higher the ratio. The researchers, led by Linda C. Ivany, a paleobiologist at Syracuse (N.Y.) University, took microscopic microscopic /mi·cro·scop·ic/ (mi?kro-skop´ik) 1. of extremely small size; visible only by the aid of the microscope. 2. pertaining or relating to a microscope or to microscopy. samples from the fossil otoliths of two types of bottom-dwelling eels. Such fish were common in the Gulf of Mexico Noun 1. Gulf of Mexico - an arm of the Atlantic to the south of the United States and to the east of Mexico Golfo de Mexico Atlantic, Atlantic Ocean - the 2nd largest ocean; separates North and South America on the west from Europe and Africa on the east both before and after the massive die-offs. Although the eels survived the extinctions at the end of the Eocene, about 90 percent of their neighboring neigh·bor n. 1. One who lives near or next to another. 2. A person, place, or thing adjacent to or located near another. 3. A fellow human. 4. Used as a form of familiar address. v. mollusk mollusk: see Mollusca. mollusk or mollusc Any of some 75,000 species of soft-bodied invertebrate animals (phylum Mollusca), many of which are wholly or partly enclosed in a calcium carbonate shell secreted by the mantle, a soft species didn't. Each tiny sample of otolith-derived calcium carbonate represents as little as 2 weeks of growth in the eel's 2-to-3-year life, Ivany notes. This enabled the scientists to measure the ancient, seasonal water temperatures where the eels lived. The oxygen-isotope ratios in the otoliths didn't show a significant difference between the summer temperatures before and after the extinctions. Winter temperatures after the die-offs, however, consistently were about 4 [degrees] Celsius colder than they were earlier, Ivany and her team report in the Oct. 19 NATURE. The larger seasonal swings in temperature probably had a significant effect on organisms Organisms See also animals; bacteria; biology; plants; zoology. anabolism Biology, Physiology. the synthesis in living organisms of more complex substances from simpler ones. Cf. catabolism. — anabolic, adj. in the Gulf of Mexico and elsewhere, Ivany says. She contends the cooler winters may have been the primary cause of the widespread extinctions at the time. Low-temperature tolerance is often critical, especially for marine organisms such as mollusks, says Thor A. Hansen, a paleontologist at Western Washington University Western Washington UniversityWWU or Western) is one of six state-funded, four-year universities of higher education in the U.S. state of Washington. It is located in Bellingham and offers bachelor's and master's degrees. in Bellingham who's studying the mollusk extinctions in the gulf. By examining otoliths, researchers can resolve seasonal temperature variations across much shorter periods than geologists typically distinguish, Hansen notes. "This is cool," he says. "It's like getting a weather report from 35 million years ago." |
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