Showing papers by "Steven M. Stanley published in 1986"

Anatomy of a regional mass extinction; Plio-Pleistocene decimation of the western Atlantic bivalve fauna

Abstract: The Early Pliocene marine faunas of the southeastern United States were distinct from those of the Bahamas and Caribbean, apparently being separatedfrom them by a zone of cool upwelling. Study of the fates of 361 Early Pliocene bivalve species reveals that a regional mass extinction occurred in the Eastern United States beginning in Late Pliocene time, when continental glaciers expanded, and continued into Early Pleistocene time, eliminating perhaps as many as 65% of the Early Pliocene species. Several patterns suggest that refrigeration during intervals of glacial expansion was the primary cause. The 57 bivalve species that have survivedfrom the tropical zone of Florida all range into nontropical zones today: the mass extinction operated as a thermal filter, eliminating all purely tropical species. Endemic Early Pliocene species experienced especially low survivorship (15%7o) and most of the casualities of these stenothermal forms came early, in Late Pliocene time. A larger percentage of eurythermal Early Pliocene species survived; and most of those that did not, died out relatively late, during cold Early Pleistocene glacial intervals when even Florida became nontropical. Several observations oppose the hypothesis that Pleistocene regressions would have caused heavy extinction even in the absence of refrigeration. Among these are (1) the fact that in the Eastern Pacific Pleistocene extinction was weak even for species endemic to the temperate-warm temperate shelf, which was areally smaller than the shelf of the southeastern United States, and (2) the fact that even Western Atlantic species that were small, abundant, and adapted to muddy conditions suffered heavy losses.

Population size extinction and speciation the fission effect in neogene bivalvia

Abstract: The extinction of a species represents reduction of both geographic range and population size to zero. Most workers have focused on geographic range as a variable strongly affecting the vulnerability of established species to extinction, but Lyellian percentages for Neogene bivalve faunas of California and Japan suggest that population size is a more important variable along continental shelves. The data employed to reach this conclusion are Lyellian percentages for latest Pliocene (-2 ma old) bivalve faunas of California and Japan (N = 245 species). These regions did not suffer heavy extinction during the recent Ice Age, and for each region the Lyellian percentage is 70%-7 1%. Discrepancies in population size appear to explain the following differences in survivorship to the Recent (Lyellian percentage) for three pairs of subgroups: (1) burrowing nonsiphonate species (42%) versus burrowing siphonate species (84%), which suffer less heavy predation; (2) burrowing nonsiphonate species of small size (73%) versus burrowing nonsiphonate species of large body size (96%); (3) Pectinacea (30%) versus other epifauna (71%), which suffer less heavy predation. During the Mesozoic Era, when predation was less effective in benthic settings, mean species duration for the Pectinacea was much greater (- 20 ma). Along the west coast of North and Central America, mean geographic range is greater for siphonate species of large body size than for siphonate species of small body size and greater still for pectinacean species. These ranges are inversely related to mean species longevity for the three groups, which indicates that geographic range is not of first-order importance in influencing species longevity. Species with non- planktotrophic development neither exhibit narrow geographic ranges along the west coast of North and Central America nor have experienced high rates of extinction in California and Japan. Rates of extinction are so high for Neogene pectinaceans and nonsiphonate burrowers that without enjoying high rates of speciation these groups could not exist at the diversities they have maintained during the Neogene Period. They are apparently speciating rapidly because of thefission efect: the relatively frequent generation of new species from populations that are fragmented by heavy predation. Thus, ironically, there may be a tendency for high rates of speciation to be approximately offset by high rates of extinction. Only if mean population size for species in a particular group becomes extremely small is it likely to result in a high rate of extinction and a low rate of speciation-and hence a dramatic decline of the group. The fission effect may contribute to the general correlation in the animal world between rate of speciation and rate of extinction.

Earth and life through time

Abstract: A revision of the best selling historical geology text, completely updated to provide a thorough but lucid introduction to the principles of historical geology. Stanley's assertion that 'the physical history and the biological history of the earth are inextricably interwined shapes his text throughout. The material is organized clearly and logically. The two-part progression resents basic principles first, then proceeds with a chronological study of the history of life. For everv interval, global events (such as general patterns of geographic change and major occurrences in the evolution and extinction of life) are reviewed within the context of plate tectonics. This review is followed bv a description of important regional events and their place within this global framework. Stanlev offers insightful observations on how environmental conditions have affected life through the ages. Numerous attractive illustrations enhance textual material. Chapter-ending reviews and exercises reinforce students' understanding and there are additional reading lists, a thorough glossary and useful appendices. Stanley has updated and improved his text to make i-t even more accessible to students. Notable changes include: Streamlined and reorganized chapter on mountain building, with new discussions of ancient plate movements Condensed and updated coverage of the Precambrian Updated and expanded discussions of mass extinctions throughout the text Additional material on isotopes and dating techniques Updated discussion of human evolution.