From McGraw-Hill encyclopedia of science and technology. McGraw-Hill Modern Men of Science; 426 Leading Contemporary Scientists Presented by the Editors of the McGraw-Hill Encyclopedia of Science and Technology. McGraw-Hill, 1966.
Born August 24, 1890, Chicago, Illinois, USA
Died March 3, 1971, Berkeley, California, USA
In his study of Tertiary forests, Chaney developed a dynamic approach based upon close resemblances between plants of the past and those now living. He considered plant fossils as representatives of the vegetation of their day, in contrast to their study as individual specimens whose structure or phylogeny is the primary concern of many paleobotanists.
Chaney's familiarity with living plants influenced his emphasis on similarities rather than on differences in designating fossil species.
But he did not use modern specific names for plants older than Pleistocene, arguing that the incompleteness of their record did not justify assuming that there had been no changes of specific rank since Tertiary time. Firmly believing that taxonomy should be a tool rather than a burden, he set up stratigraphic species where differences in size or other minor characters could be detected in rocks of different ages. In like manner he tended to establish geographic species for similar plants separated by ocean or climatic barriers. Recognition of elements whose fossils had close living equivalents in major areas did much to clarify areal and systematic relationships of fossil plants to each other and to those that have survived in modern forests.
Chaney's collecting procedure required handling of large numbers of specimens, so that variations within designated fossil species could be compared with those of related living plants. A census taken in the field showed which species were abundant near sites of deposition, and perhaps suggested more remote habitats in adjacent uplands for sparsely represented plants.
A standard section was set up in the John Day Basin of eastern Oregon, where abundant and well-preserved fossils occurred in stratigraphic sequence. Successive floras showed differences in composition, and Chaney noted a progressive reduction in size and texture of leaves. This provided a basis for dating the floras of other areas, and for their assignment to the same stage in the Tertiary sequence if they occurred in the same general latitude.
Quantitative appraisal of leaf characters provided a basis for estimating Tertiary climates. Large, thick, camptodrome-veined leaves now characterize the evergreen forests of the tropics, while trees of higher latitudes are largely deciduous, with smaller, thinner leaves, and craspedodrime venation. The change in leaf characters from Lower to Upper Tertiary shows a response to progressive changes toward the cooler and drier climate of our day.
Chaney pointed out that the temperate Eocene plants of Alaska did not appear in Oregon until Oligocene time, and that subtropical Eocene plants of Oregon have survived only in low latitudes. He suggested the term "geoflora" for groups of plants in mass migration; the Arcto-Tertiary Geoflora has maintained itself with only minor changes in composition since the Eocene, during which time its distribution has been shifted from Alaska southward across the United States. The Neotropical-Tertiary Geoflora has moved from Washington and Oregon into Mexico and Central America. Recognition of a deciduous conifer, Metasequoia, as a fossil by S. Miki in 1941, and its almost contemporary discovery as a living tree by T. Wang in central China, has done much to confirm the concept of geofloras. Chaney had previously predicted that a fossil "redwood" might be discovered, with a deciduous habit suited to occurrence at high latitudes. He visited the natural occurrence of Metasequoia in 1948 to determine that its associates were members of the Arcto-Tertiary Geoflora, and revised the fossil records of several members of the Taxodiaceae.
Most fossil floras contain plants that lived at low to middle altitudes. Chaney suggested that since the lapse rate corresponds to successively lower temperatures at higher latitudes, an Eocene flora living near sea level in Alaska may have had a counterpart in the mountains of Oregon; its absence or scant representation in the Oregon Eocene was to be expected in view of its remoteness from sites of deposition, but we could reconstruct such a montane flora by studying floras of similar age in deposits to the north. An early elaboration of this concept led to his suggestion that angiosperms may have had their origin at high altitudes during the Jurassic period, although they first appeared in the fossil record in Cretaceous time.
While there has been well-defined latitudinal control of forest distribution during the Tertiary period, Chaney noted significant departures. A given flora lived farther south with increasing distance from the Pacific Coast; it ranged far to the north across ocean basins. Plotting the occurrence of Eocene floras across North America and Eurasia, he showed that lines connecting similar floras (isoflors) followed the paths of modern isotherms and of major forest types. He concluded that Eocene position of continents and oceans in relation to each other and to the axis of rotation was essentially the same as it is today. This placed the burden of proof on advocates of continental drift and polar migrations during later geologic time.
A descendant of pioneer Illinois farmers, Chaney majored successively in zoology, botany, and geology at the University of Chicago, where he received his B.S. in geology in 1912 and his Ph.D. in paleontology in 1919. Several years of high-school and university teaching (State University of Iowa) preceded his appointment in 1922 as research associate of the Carnegie Institution of Washington; he retired in 1957. From 1930 until 1957, he was also professor of paleontology at the University of California, Berkeley. He carried on field work widely in the Americas and Asia. During World War II he set aside his paleobotanical work to become assistant director of the University's Radiation Laboratory in an administrative capacity. He was elected to the National Academy of Sciences in 1947.
For background information see Paleobotany in the McGraw-Hill Encyclopedia of Science and Technologu.
Posts
No comments :
Post a Comment