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Devonian bryozoan diversity, extinctions, and originations
- Alan S. Horowitz, Joseph F. Pachut, Robert L. Anstey
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- Journal:
- Journal of Paleontology / Volume 70 / Issue 3 / May 1996
- Published online by Cambridge University Press:
- 20 May 2016, pp. 373-380
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Observed diversity of bryozoans within Devonian stages is not significantly different from range-through values for species because very few species have ranges longer than a single stage. Generic diversity differs significantly between observed stadial and stadial range-through values except for the diverse Givetian faunas. Among families, observed stadial and range-through comparisons differ significantly in the lower diversity Early and Late Devonian but are not significant in the taxonomically diverse Middle Devonian. The patterns of Devonian generic and familial diversity are apparently robust proxies for specific diversity.
Givetian specific and generic extinctions, based on generated bootstrap distributions, are significantly higher than the other six Devonian stages even when modifications for different stage durations are considered. Based on present data, we conclude that a major change in Devonian diversity occurred between the Givetian and the Frasnian stages. Givetian specific and generic extinctions are not “smeared” with respect to adjacent stages and should qualify as a mass extinction among bryozoans pending more accurate data on bryozoan ranges and more precision in radiometric dating of Devonian stadial boundaries. Devonian bryozoan familial extinctions are not numerous and do not exhibit a significant number of extinctions for any stage. The Givetian extinction, which for the time being ranks as the largest bryozoan extinction in the Phanerozoic, is a global event with a marked local effect in the Hamilton-Tully fauna of New York, Pennsylvania, and Ontario.
Givetian specific originations are significantly higher than bootstrap distributions for both raw data and data modified for stadial durations. A Givetian generic high in originations for raw data is not significant when modified for stadial durations and only Eifelian familial originations are significantly higher than bootstrapped distributions.
Conodont paleontology of the Providence Limestone Member of the Dugger Formation (Pennsylvanian, Desmoinesian) in the southern part of the Illinois Basin
- Lewis M. Brown, Carl B. Rexroad, Donald L. Eggert, Alan S. Horowitz
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- Journal of Paleontology / Volume 65 / Issue 6 / November 1991
- Published online by Cambridge University Press:
- 20 May 2016, pp. 945-957
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The Providence Limestone member of the Dugger Formation in Indiana and its lithologic correlatives in the southern part of the Illinois Basin are thin lime mudstones to packstones lying stratigraphically between the Herrin and Hymera Coal Members of the Dugger Formation and their equivalents. The purposes of the study are to describe and correlate the Providence conodont fauna and to apply biofacies analysis and petrographic study to interpreting the paleoenvironments.
Providence conodonts are dominated by representatives of the Idiognathodus-Streptognathodus plexus. Hindeodus is abundant; Neognathodus is common; and Idioprioniodus, Adetognathus, and Diplognathodus are common only in some sections. Aethotaxis is a minor constituent.
Conodont biofacies reflect a shallow, nearshore, low- to moderate-energy marine environment. The Idiognathodus-Streptognathodus plexus indicates quiet to moderately elevated energy levels. Hindeodus replaces part of the Idiognathodus-Streptognathodus plexus in higher energy conditions. Diplognathodus has an affinity for low to slightly elevated energy conditions. Migration during ontogeny to quite, organic-rich water from a more open, slightly higher energy environment is indicated for Streptognathodus oppletus.
Assignment to the Neognathodus dilatus-N. roundyi zone indicates a middle Desmoinesian age. The new species Diplognathodus indianaensis is morphologically intermediate between the early Desmoinesian D. coloradoensis and the late Desmoinesian D. illinoisensis and allows refinement of a Diplognathodus-based zonation.
The H. A. Nicholson Collection of Paleozoic stenolaemate bryozoans: comparison of cladistic and phenetic classifications
- Joseph F. Pachut, Robert L. Anstey, Alan S. Horowitz
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- Journal:
- Journal of Paleontology / Volume 68 / Issue 5 / September 1994
- Published online by Cambridge University Press:
- 20 May 2016, pp. 978-994
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Until the late 1960's, most of Nicholson's types of Paleozoic bryozoans were not available for study. We present a set of coded characters of many of Nicholson's types, which should assist in bringing his species into conformity with current taxonomic standards so that his species can be consistently recognized and used in biostratigraphic, paleobiogeographic, and evolutionary studies.
Cladistic and phenetic analyses of these species permit comparisons between inferred phylogenies of Nicholson specimens, adaptive morphospace, and treatise-based systematic relationships. Specimen-based cladistic and phenetic analyses of Nicholson's species both produce clusters that are congruent with existing family-level taxonomic assignments of species in the collection. However, cladistic analysis more fully retrieves the pattern of branching, or degree of relatedness, among higher taxa. Phenetic clusters represent adaptive peaks in morphospace for these specimens, but higher level “phenons” are strongly affected by multiple evolution of the same character states.
Abnormalities in Pentremites Say (Blastoidea) from the Pella Formation (Upper Mississippian) of Iowa
- Alan S. Horowitz, Susan Able, H. L. Strimple
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- Journal:
- Journal of Paleontology / Volume 60 / Issue 2 / March 1986
- Published online by Cambridge University Press:
- 19 May 2016, pp. 390-399
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Approximately 10,000 determinable specimens of Pentremites pulchellus Ulrich (Blastoidea, Echinodermata) from a single quarry in the Pella Formation near Oskaloosa, Mahaska County, Iowa, have been examined for abnormal morphologic characters. The total frequency (2.7%) and the frequency among different types of abnormalities (ambulacral 29%; basal 46%; symmetrical 12%) are significantly different in the Pella material than in previously published studies (Wanner, 1932; Macurda, 1980). The greater frequency of abnormalities in the Pella Formation than in previous studies may reflect higher environmental stress because of variable temperatures or salinities or both. The kinds of abnormalities are the same among published studies, which suggest that the underlying biological causes of abnormalities were similar throughout the geologic history of the blastoids. Ambulacral abnormalities are symmetrically distributed, but the division and inversion of basal plates show an asymmetrical distribution as previously recorded by Macurda (1980). The Pella Formation is of Genevievian age (Upper Mississippian) based on the occurrence of Pugnoides ottumwa (White) and convex ambulacra in Pentremites pulchellus. Other unequivocal guide fossils are unknown in the Pella Formation.
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- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
- Edited by Robert Audi, University of Notre Dame, Indiana
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- The Cambridge Dictionary of Philosophy
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- 05 August 2015
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- 27 April 2015, pp ix-xxx
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- By Rony A. Adam, Gloria Bachmann, Nichole M. Barker, Randall B. Barnes, John Bennett, Inbar Ben-Shachar, Jonathan S. Berek, Sarah L. Berga, Monica W. Best, Eric J. Bieber, Frank M. Biro, Shan Biscette, Anita K. Blanchard, Candace Brown, Ronald T. Burkman, Joseph Buscema, John E. Buster, Michael Byas-Smith, Sandra Ann Carson, Judy C. Chang, Annie N. Y. Cheung, Mindy S. Christianson, Karishma Circelli, Daniel L. Clarke-Pearson, Larry J. Copeland, Bryan D. Cowan, Navneet Dhillon, Michael P. Diamond, Conception Diaz-Arrastia, Nicole M. Donnellan, Michael L. Eisenberg, Eric Eisenhauer, Sebastian Faro, J. Stuart Ferriss, Lisa C. Flowers, Susan J. Freeman, Leda Gattoc, Claudine Marie Gayle, Timothy M. Geiger, Jennifer S. Gell, Alan N. Gordon, Victoria L. Green, Jon K. Hathaway, Enrique Hernandez, S. Paige Hertweck, Randall S. Hines, Ira R. Horowitz, Fred M. Howard, William W. Hurd, Fidan Israfilbayli, Denise J. Jamieson, Carolyn R. Jaslow, Erika B. Johnston-MacAnanny, Rohna M. Kearney, Namita Khanna, Caroline C. King, Jeremy A. King, Ira J. Kodner, Tamara Kolev, Athena P. Kourtis, S. Robert Kovac, Ertug Kovanci, William H. Kutteh, Eduardo Lara-Torre, Pallavi Latthe, Herschel W. Lawson, Ronald L. Levine, Frank W. Ling, Larry I. Lipshultz, Steven D. McCarus, Robert McLellan, Shruti Malik, Suketu M. Mansuria, Mohamed K. Mehasseb, Pamela J. Murray, Saloney Nazeer, Farr R. Nezhat, Hextan Y. S. Ngan, Gina M. Northington, Peggy A. Norton, Ruth M. O'Regan, Kristiina Parviainen, Resad P. Pasic, Tanja Pejovic, K. Ulrich Petry, Nancy A. Phillips, Ashish Pradhan, Elizabeth E. Puscheck, Suneetha Rachaneni, Devon M. Ramaeker, David B. Redwine, Robert L. Reid, Carla P. Roberts, Walter Romano, Peter G. Rose, Robert L. Rosenfield, Shon P. Rowan, Mack T. Ruffin, Janice M. Rymer, Evis Sala, Ritu Salani, Joseph S. Sanfilippo, Mahmood I. Shafi, Roger P. Smith, Meredith L. Snook, Thomas E. Snyder, Mary D. Stephenson, Thomas G. Stovall, Richard L. Sweet, Philip M. Toozs-Hobson, Togas Tulandi, Elizabeth R. Unger, Denise S. Uyar, Marion S. Verp, Rahi Victory, Tamara J. Vokes, Michelle J. Washington, Katharine O'Connell White, Paul E. Wise, Frank M. Wittmaack, Miya P. Yamamoto, Christine Yu, Howard A. Zacur
- Edited by Eric J. Bieber, Joseph S. Sanfilippo, University of Pittsburgh, Ira R. Horowitz, Emory University, Atlanta, Mahmood I. Shafi
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- Clinical Gynecology
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- 05 April 2015
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- 23 April 2015, pp viii-xiv
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Bryozoan Phanerozoic Species Diversity
- Alan S. Horowitz, Joseph F. Pachut
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- Journal:
- The Paleontological Society Special Publications / Volume 8 / 1996
- Published online by Cambridge University Press:
- 26 July 2017, p. 179
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- 1996
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Bryozoan Rebound(?) From Permian Extinctions
- Alan S. Horowitz, Joseph F. Pachut
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- The Paleontological Society Special Publications / Volume 8 / 1996
- Published online by Cambridge University Press:
- 26 July 2017, p. 180
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- 1996
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Devonian bryozoan extinction and diversification
- Alan S. Horowitz, Joseph F. Pachut
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- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 136
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- 1992
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The names proposed world-wide for Devonian bryozoans have been evaluated with respect to replaced names, synonyms, and nomina dubia [Horowitz and Pachut (1993), Journal of Paleontology, in press]. The resulting list contains 1738 specific names assigned to 199 genera in 45 families. Approximately 75% of Devonian bryozoan species are reported from a single stage. Not more than 10%, and usually 4–6%, of the species reported in any Devonian stage are also reported in the succeeding stage.
The largest decrease in observed bryozoan diversity occurs between the Givetian and Frasnian stages, reducing the number of species by 77%, genera by 64%, and families by 42%. These values are less than those reported for the range-through method for the entire fauna of the Permian mass extinction (Raup, 1979) but larger than percentage extinctions (presumably based on range-though data) for four other Phanerozoic mass extinctions tabulated by Valentine and Walker (1987).
The range-through method dampens the observed differences in taxonomic diversity among Devonian stages at all taxonomic levels. The range-through number of species/stage is based upon both direct applications of the range-through method and on the assignment of ranges known only to early, middle and late Devonian to include appropriate Devonian stages. Generic and familial diversity increases monotonically from Lochkovian through Givetian stages. Thereafter (Givetian to Frasnian), range-through values for specific (69%), generic (31%), and familial diversity (10%) decrease. Specific and familial decreases across the Givetian-Frasnian boundary are comparable to those reported for non-Permian mass extinctions by Valentine and Walker, but the generic decrease is not as great. These results are consistent with Valentine and Walker's random mass extinction model.
Observed bryozoan diversity across the Frasnian-Famennian boundary increases while values calculated using the range-through method decrease by approximately 5–15%. This does not suggest a major bryozoan extinction event. Conversely, the decrease in bryozoan diversity across the Givetian-Frasnian interval is similar to an important Devonian extinction among rugose corals. The reason(s) for these extinctions is not yet clear. With respect to Devonian bryozoans, our inadequate understanding of the cause(s) of mass extinctions and the relatively coarse resolution of the stadial timescale does not permit differentiating between gradual or catastrophic scenarios.