Vol. 6, No. 10 October 1996 INSIDE • First International Secretary Named, p. 22 • 1996 Honorary Fellows, p. 23 GSA TODAY • Call for Award Nominations, p. 26 A Publication of the Geological Society of America • Southeastern Section 1997 Meeting, p. 32
Out of the Icehouse into the Greenhouse: A Late Paleozoic Analog for Modern Global Vegetational Change Robert A. Gastaldo, Department of Geol- ogy, Auburn University, AL 36849-5305, William A. DiMichele, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20506, Hermann W. Pfefferkorn, Department of Geology, University of Pennsylvania, Philadelphia, PA 19104-6316 L
ABSTRACT A change to global greenhouse con- ditions following deglaciation occurred during the late Paleozoic. The deep-past data set preserved in the stratigraphic C record can serve as a model system to understand vegetational responses dur- ing this kind of climatic change, espe- cially in the tropics. No other time in Earth history so mimics the late Ceno- FSSP zoic or provides the long-term data set from which generalizations can be Figure 1. Reconstruction of middle late Carboniferous tropical coal swamp showing different plant deduced. Two long-term glacial cycles communities made up of tree lycopods (L, tree club mosses), tree sphenopsids (two brushlike trees above letter S in center and tree scouring rushes), tree ferns (F), pteridosperms (P, seed plants with have been identified in Permian-Car- fernlike leaves; extinct group), and cordaites (C, seed plants with strap-shaped leaves; extinct group). boniferous time. The waxing and wan- From a painting by Alice Prickett, published in black and white in Phillips and Cross (1991, pl. 4). ing of glaciers during the height of either ice age resulted mainly in spatial displacement of vegetation, and also in minor variations in tropical climate. spatial distribution of plants in the the rates, geographic distribution, and Brief intervals of rapid deglaciation at tropics and temperate zones, and nearly nature of vegetational changes can serve the end of the Middle Pennsylvanian synchronous changes in the structure as portents of similar patterns in the (Westphalian) and mid–Early Permian of vegetation throughout the globe. transition to a modern greenhouse (Sakmarian) were accompanied by Although the plants of the late Paleo- world. major changes in plant assemblages, zoic and the geography of that time including extinctions, changes in the differed entirely from those of today, Greenhouse continued on p. 2
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2 GSA TODAY, October 1996 Greenhouse continued from p. 2 time over which these turnovers occurred. change of climatic patterns and greater However, the resolution of time within oscillations in seasonal moisture availabil- tal processes and permitting generaliza- stratigraphic sections is increasing. In spe- ity in the tropics. Specifically, there are tions to be made about how vegetation cific cases it is possible to constrain time much larger areas that experience strong responds to changing climate. The late either in the range of orbital cycles or even wet-dry seasonality. Paleozoic plant record consists of assem- months for tidal sediments. In the near During the Middle Pennsylvanian blages that are preserved with high resolu- future we can expect to find stratigraphic (Westphalian) ice age, the waxing and tion and fidelity (Behrensmeyer and Hook, sections that will allow us to put numeri- waning of polar ice caps and glaciers were 1992; Burnham, 1993) in sedimentary cal values both on the duration of change- represented in the Euramerican tropics by environments representing fluvial, lacus- overs and on intervals of stasis. We cyclical sedimentary patterns. During Mid- trine, coastal plain, and deltaic settings. expect change-overs to be in the range dle Pennsylvanian (Westphalian) glacial Plants colonized a wide variety of sub- of 1–10 ka. maxima, extensive peat-accumulating strates, and communities are known from swamps developed under an ever-wet cli- peat and clastic alluvial sediments. These LATE PALEOZOIC GLACIATION mate. Marine sediments reflecting a wide assemblages provide snapshots in time of variance in climate were deposited during Polar glaciation began in the latest vegetational patterns during both glacial interglacial periods (glacial minima). Such early Carboniferous (Visean-Namurian) and interglacial cycles over the entire ice- sea-level changes are evidenced by paralic and fluctuated in magnitude throughout house-greenhouse interval. Finally, late sequences bounded by transgressive ero- the Permian-Carboniferous (Fig. 2). Dur- Paleozoic tropical plants and plant ecosys- sional surfaces (Gastaldo et al., 1993) and ing these 75+ m.y., two ice ages peaked, tems are as well known as and possibly may be covariant with changes from ever- one during the late Middle Pennsylvanian better known than their Holocene coun- wet to seasonally dry climates (Cecil, (late Westphalian) and the other in the terparts, in terms of their long-term 1990). During the Early Permian glacia- Early Permian (Sakmarian). Orbital-driven response to abiotic stresses (sea level and tions, in contrast to the Westphalian, peat glacial and interglacial oscillations were climate fluctuations). From the late Paleo- accumulation was far more limited and superimposed on these long-term trends zoic record, we conclude that many effects localized in areas of wettest tropical cli- (Frakes et al., 1992). The maximum extent of an icehouse-greenhouse transition will mates. Interglacials of that time period of ice caps expanded gradually over the probably be expressed dramatically in the also were more intensely seasonal than continents, taking an estimated 20 m.y. to tropics. comparable intervals in the Westphalian, reach their greatest coverage. Increasing The late Paleozoic encompasses the on the basis of vegetational and paleosol evidence indicates that each ice age termi- decline of Earth’s primeval forests and patterns (Broutin et al., 1990). nated abruptly over 1–10 ka. their replacement by seed-plant-domi- During the Late Pennsylvanian The extent of polar glaciations (cover- nated vegetation more typical of the (Stephanian), which falls between the two age and ice mass) during Milankovitch Mesozoic. Increases in greenhouse gasses ice ages, Earth may have been warmer cycles has a direct effect on the distribu- during the late Paleozoic occurred over (Dorofyeva et al., 1982). Evidence from tion of rainfall in the tropics by affecting millions of years (Berner, 1990, 1991; coal-resource distributional patterns the pattern of atmospheric circulation and Graham et al., 1995). In contrast, similar (Phillips and Peppers, 1984) and from bio- the latitudinal range and width of the accumulations may occur within markedly facies analysis (DiMichele and Aronson, intertropical convergence zone (Ziegler shorter intervals of time today (Francey et 1992) indicates a generally drier or more et al., 1987; Pfefferkorn, 1995). During al., 1995). However, the time required for seasonal Late Pennsylvanian (Stephanian) glacial maxima, the intertropical conver- changes in plant life might not be signifi- interval with pulselike oscillations gence zone contracts toward the equator cantly different. While late Paleozoic between overall wetter and drier periods. and migrates over a narrower latitude, stages, as defined by plant fossils, lasted These oscillations continued into the Per- resulting in ever-wet conditions within its from 1 to 2 m.y., the change from one mian, with an increasing prominence of area of influence. In contrast, during inter- flora to another (widespread extinction, drier climates in tropical lowland and glacial intervals, the intertropical conver- radiation, and propagation) marks the intermontane areas. Drying continued gence zone expands latitudinally and boundary between stages. We cannot yet migrates during the yearly cycle over a put numerical values on the length of Greenhouse continued on p. 4 wider latitudinal belt, resulting in a
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GSA TODAY, October 1996 3 Greenhouse continued from p. 3 throughout the Permian, and ice caps and peat-accumulating systems were lost (Retallack, 1995). By latest Permian time, compressional tectonics, the oxidation of peat resources, and volcanic processes may have introduced vast quantities of CO2 into the atmosphere, driving global tem- peratures toward their maximum (Erwin, 1996).
LATE PALEOZOIC VEGETATION The beginning of the Carboniferous is marked by a radiation of vascular plants that established five major groups. During the late Paleozoic, ecological dominance was strongly partitioned by the different higher taxonomic groups (see Fig. 1): tree club mosses (rhizomorphic lycopsids) in swampy wetlands; tree scouring rushes Figure 2. Relation between global glaciation and vegetative change during the late Paleozoic in different (sphenopsids) in aggradational environ- tropical environments and the north and south temperate belts. Glacial ice extent, from Frakes et al. ments; ferns, including tree ferns, as weeds (1992), is based upon tillites (glacial) and ice-rafted deposits (IRD). Vegetation distributional patterns in a variety of disturbed settings; and seed are derived from sources cited in the text. M = Mississippian; Pa = Pennsylvanian; E = Early; L = Late; plants (seed ferns or pteridosperms and VIS = Visean; NAM = Namurian; WES = Westphalian; STE = Stephanian; ASS = Asselian; SAK = Sakmarian; cordaites) in better drained habitats. How- ART = Artinskian; KUN = Kungurian; KAZ = Kazanian; TAT = Tatarian; CHES = Chesterian; MORR = Mor- ever, temporal and spatial exceptions are rowan; ATOK = Atokan; DESM = Desmoinesian; MISS = Missourian; VIRG = Virgilian; WOLF = Wolf- campian; LEON = Leonardian; GUAD = Guadalupian. known to have existed—as, for example, peat-forming cordaites and pteridosperms. The dominance of each group of plants in a particular environment distinguishes the Carboniferous from later time periods. By Figure 3. Distribution of the end of the Paleozoic, these patterns floral realms in latest and groups had yielded, through a series Pennsylvanian time of steps, to seed plants, which began to (290 Ma). Northern dominate in most habitats throughout temperate (Angara), tropical the world (Niklas et al., 1983). (Euramerica), and southern Permian-Carboniferous terrestrial veg- temperate (Gondwana) realms can be distinguished. etation can be divided into three broad Continental position biogeographic realms (Fig. 3): (1) the redrawn from Denham and pantropical Euramerican (or Amerosinian) Scotese’s 1988 computer floral realm (Wagner, 1993), the best program, Terra Mobilis. known and most intensively studied, (2) the north-temperate Angaran floral realm (Meyen, 1982), and (3) the south-temper- ate Gondwanan floral realm (Archangel- Major vegetational changes have been includes a “wet” biome, characterized by sky, 1990). These three biogeographic noted at the base of the Late Carbonifer- mire (peat-forming) and clastic (flood- realms were occupied by different plants, ous, within the Early Pennsylvanian plain) wetland vegetation. These are the but the vegetational turnover occurred in (Namurian), near the Middle-Upper Penn- plants typically reconstructed in most Car- all three at about the same time (Wagner, sylvanian (Westphalian-Stephanian) boniferous “coal swamp” dioramas. Less 1993). However, there might be differ- boundary, during the transition from the well known, but present throughout most ences in the timing of turnover of as much Carboniferous to the Permian, and near of the Late Carboniferous, was a tropical as one stage between different climatic the Sakmarian-Artinskian boundary. Each “dry” biome with a flora rich in gym- belts, owing to the buffering of environ- changeover corresponds to significant nosperms and which included conifers mental change by local or regional physio- increases or decreases in polar ice volumes (Lyons and Darrah, 1989). This flora graphic differences and the resulting lag and global temperature (Fig. 2). In all entered the tropical lowlands only during time in vegetational turnover. These major these cases and in all parts of the world, short periods of regional dryness (probably vegetational turnovers appear to be in part the patterns of vegetational organization the result of increased seasonality; Elias, the result of geologically rapid (1–10 ka) yield to increased dominance by oppor- 1936; DiMichele and Aronson, 1992). migrations of groups of plants from one tunistic weedy taxa or, ultimately, to the Mires within the “wet” biome were climatic belt to another. In contrast, slow extinction-resistant life histories of seed dominated by lycopsids and cordaites migration of genera or species over mil- plants. throughout the Middle Pennsylvanian lions of years has been documented by (Westphalian); tree ferns appeared in mires Laveine (1993). These two processes are TROPICAL PATTERNS of the latest Middle Pennsylvanian different in nature and should not be con- (mid–Westphalian D). Following major Each of the floral realms can be subdi- fused. Knowledge of the slow migration extinctions at the Middle-Late Pennsylva- vided into “biomes” characteristic of par- can improve our understanding of biogeo- nian (Westphalian-Stephanian) boundary ticular climatic and ecological conditions, graphic barriers during times of evolution- that reached nearly 70% of the known and each is further subdivisible into land- ary stasis. species (DiMichele and Phillips, 1996), scape units. The Euramerican realm
4 GSA TODAY, October 1996 elsewhere in the world during the Per- mian. The transition from the wet to the dry biome was not accompanied by exten- sive mixing of the component species. Figure 4. Changes in domi- Rather, each retained its distinctive taxo- nance patterns of major plant nomic and ecomorphic characteristics. groups in the clastic swamp At this temporal scale, replacement rather environment of the tropics throughout the Pennsylvanian than a competitive displacement is (late Carboniferous) and earli- strongly indicated. Additionally, it appears est Permian. Data from North that higher levels of ecological organiza- America and Europe (Pfeffer- tion may have spatial-temporal unity korn and Thomson, 1982). and take part in dynamics not predictable from the study of lower level population or community dynamics. The biomic tran- sition appears to have been independent of internal vegetational dynamics that occurred within each biome. The dry biome became increasingly dominated by conifers in parts of Euramerica throughout the Asselian (Broutin et al., 1990). It was not until the Figure 5. Changes in dominance Sakmarian-Artinkskian deglaciation that patterns of major plant groups in tree ferns re-emerged as dominant ele- the clastic swamp environment ments within a vegetation that was char- of the northern temperate realm acterized by a diversity of seed plants throughout the Pennsylvanian (Read and Mamay, 1964). Their re-emer- (late Carboniferous) and Per- gence indicates a change to increased mian. Data from Kazakhstan (Meyen, 1982). moisture availability within the tropics. NORTH-TEMPERATE PATTERNS The Angara floral realm was domi- nated by a lycopsid-rich flora prior to the onset of polar glaciations (Fig. 5). At or near the middle to late Namurian bound- tree ferns dominated Late Pennsylvanian ent conditions. This signaled the begin- ary, the lycopsid flora was replaced by a mires. ning of the breakdown of the landscape low-diversity but widespread flora domi- Clastic wetland habitats were largely between groups of plants. The high taxo- nated by seed ferns and cordaiteans pteridosperm dominated throughout the nomic level at which the data are summa- (Ruflorians) that were persistent through- Middle Pennsylvanian (Gastaldo, 1987). rized in Figures 2, 4, and 5 masks certain out the Middle Pennsylvanian wetlands. Beginning in the latest Middle Pennsylva- patterns at lower levels of ecological Near the Middle Pennsylvanian–Late nian, tree ferns rapidly established them- organization, particularly the persistence Pennsylvanian boundary a further floristic selves as codominants and continued as of dominance-diversity patterns within change ensued, resulting in the rise of dominant to codominant taxa throughout habitats and the replacement of species high-diversity cordaite-dominated assem- the Late Pennsylvanian (Pfefferkorn and on ecomorphic themes through time blages (Ruflorian 2 assemblage) (Meyen, Thomson, 1982). The predominance of (DiMichele et al., 1996). The major pat- 1982); Wagner (1993) suggested that this tree ferns during the Late Pennsylvanian terns revealed by these data are persistence floral change may be coeval with time- followed extinctions in the clastic wet- of communities and landscapes over mil- equivalent tropical vegetational changes. lands that, although less severe, paralleled lions of years, disrupted only by major The pteridospermalean (seed fern) compo- those of the mires. The extinctions within extinction events that lead to relatively nent of the Angaran Middle Pennsylva- the pteridosperm groups were accompa- rapid reorganization and establishment nian flora is the major casualty following nied by speciation that vastly increased of new persistent patterns. vegetational reorganization. The subse- the number of tree fern taxa of the later In spite of renewed polar glaciation, quently dominant, cordaite-rich floras Paleozoic (Fig. 4). pulselike climatic drying continued (Ruflorian 3) have been suggested to be The extinction events at the Middle throughout the tropics into the Early Per- tolerant of freezing conditions. As in the Pennsylvanian–Late Pennsylvanian (West- mian. Continued drying, in part the result tropical zone, the floras of Angara become phalian-Stephanian) boundary induced of Pangean assembly, progressively elimi- progressively more enriched in and domi- a thresholdlike internal reorganization nated tracts of continuous wetland habitat nated by other seed plants (gymnosperms) of the wetlands (DiMichele and Phillips, crucial to the survival of the wet biome. as major climatic changes caused extinc- 1995). The tree ferns that became domi- The exception occurs in south China, tions in, and reorganizations of, the nant descended from opportunistic weedy where a Westphalian-type flora persisted regional ecological structure (Fig. 5). forms in the older Westphalian land- in mires until the Late Permian (Guo, scapes. These plants were well suited to 1990). Seed plants, which were resistant SOUTH-TEMPERATE PATTERNS compete for space and resources in dis- to increasingly dry conditions by virtue of As in the tropical and north temper- rupted, postextinction landscapes, owing both reproductive and vegetative adapta- ate zones, the Gondwana zone had several to their reproductive strategy of producing tions, became the dominant elements in distinct vegetational regions in the late massive quantities of highly dispersible most tropical habitats, even in geographi- Paleozoic (Cuneo, 1996b). The northern- spores, a “cheaply” constructed body (one cally isolated patches of wetlands. The most parts of the Gondwana continent consisting largely of simple parenchyma Chinese “refugium” never served as a cells), and an ability to tolerate low nutri- source for repopulation of the wetlands Greenhouse continued on p. 6
GSA TODAY, October 1996 5 Greenhouse continued from p. 5 conifers, sphenopsids, ferns, pteri- The concept of refugium is elusive. dosperms, ginkgophytes, and cordaites. An area of survival of archaic vegetation (northern South America and North One aspect that has been neglected in (relative to the rest of a floristic realm) Africa) were in the tropics, and fossil most previous discussions is the fact that does not constitute a refugium if the assemblages from these areas are distinctly there must have been glacial and inter- plants cannot migrate back to previously Euramerican. All other parts of the conti- glacial intervals and that the interglacial occupied areas when conditions return to nent were in the south temperate Gond- periods could have been very warm, pro- those approximating the pre-extinction wana biogeographic zone. Major floral viding for part of the vegetational record. environment. Both abiotic factors, such as changes occurred on the Gondwana conti- the lack of clear routes of dispersal, and nent in the Southern Hemisphere at or DISCUSSION biotic factors, such as incumbent advan- near the mid-Carboniferous and Carbonif- tage, can prevent an expansion of vegeta- The late Paleozoic offers the best pre- erous-Permian boundaries. Prior to the tion from a potentially refugial area. Pleistocene opportunity to observe the mid-Carboniferous and the inception of Ultimately, species with life histories response of terrestrial vegetation to short- glaciation, biomes were characterized by and structural adaptations that precondi- term and long-term fluctuations in glacial progymnosperms and pteridosperms. tion them to survive under physically conditions, the ultimate end of an ice age, There is still debate as to the exact timing inhospitable conditions will survive to and change to a global greenhouse. In of floral change, because the onset of attain dominance. During the late Paleo- fact, the patterns of change in the tropics, glaciation may have affected the plant bio- zoic these were almost exclusively groups in particular, appear to be better docu- geography in continental interiors earlier of seed plants. The pattern has continued, mented for the Permian-Carboniferous (Archangelsky, 1990). with subsequent global and regional eco- tropics than for those of today. Several Floristic turnover at the mid-Car- logical perturbation resulting in domi- conclusions and generalities can already boniferous boundary is characterized nance of the landscape by an ever narrow- be drawn from study of these long-extinct by a flora that was made up of taxa like ing phylogenetic spectrum of plants after ecosystems. Nothorhacopteris, which appear to be simi- the late Paleozoic. Within the seed plants, Despite difficulties in correlation, a lar in aspect to forms dominating early dominance has been narrowed largely to case can be made for approximate syn- Carboniferous floras in the tropics. Several angiosperms. Within angiosperms, com- chroneity of changes in plant communi- of the dominant taxa were considered to posites and grasses have become ever more ties throughout the world in response to be progymnosperms. However, recent dominant over wider areas of Earth’s sur- severe global physical stresses. These con- work has shown that some of them were face as a consequence of climatic changes. sequences might be offset in time by as pteridosperms (Vega and Archangelsky, Patterns in the late Paleozoic provide much as a stage because some climatic 1996; Galtier, 1996). Scouring rushes us with one certainty: global warming pre- belts or environments are able to buffer (sphenopsids) and club mosses (lycopsids) sents plants with conditions that are consequences of changes until threshold also were present, but they were small in markedly different from those found dur- levels are overcome. The “recovery” the cooler areas; they grew to tree size ing periods of icehouse climate. The wax- phases following periods of major glacial only in the warmer areas (Peru, Niger). ing and waning of glaciers are, in and of onset or retreat are complex and depen- Ferns were rare or absent. The highest themselves, a climate-mode to which veg- dent on local factors, both biotic (for diversity floras occupied the lower lati- etations become attuned. Global warming example, ability of species to extend their tudes, whereas the low-diversity floras are breaks the mold and encourages the estab- ranges into an area) and abiotic. known from more poleward regions. lishment, quite rapidly (in geological Ecosystems appear to be able to At or near the Carboniferous-Permian terms at a stage boundary; probably on “absorb” regional to global species extinc- boundary, this late Carboniferous flora the order of 1–10 ka), of new kinds of veg- tions below some threshold level. Our was replaced by one dominated by seed- etation, the origins of which are as much data do not yet permit us to pinpoint this bearing glossopterids, large trees with due to evolutionary innovation as to reor- with great accuracy, but it appears to be deciduous leaves (Cuneo, 1996a). Early ganization of species associations. Extinc- less than 50% and probably more than glossopterids appeared suddenly, accom- tions break the hold incumbent taxa have 10% of common species of trees and panied by the extinction of many of the over the resources and favor or permit the shrubs. Such background turnover and Carboniferous elements. The simple vena- establishment of new species, although replacement are visible at the species level tion of these early forms cannot be distin- apparently those descended from oppor- in data derived from peat-forming mires guished from the genus Lesleya that tunistic and/or extinction-resistant ances- and clastic wetlands. When this threshold occurred in seasonally dry areas of the tors. Past patterns, when coupled with extinction level is surpassed, reorganiza- tropics as early as earliest Pennsylvanian recently developed ecological concepts tion takes place and results in a different (Namurian) time in Illinois (Leary, 1980). such as the recognition of thresholdlike dominance-diversity structure. Floras and If actually related to glossopterids, Lesleya responses to perturbation (Kareiva and vegetation in both the tropical and north- would have been at least partly preadapted Wennergren, 1995), provide a basis to temperate regions persist for millions of to a seasonally cold climate of the South- speculate on responses to change. years despite background extinction, only ern Hemisphere (Leary, 1980; Archangel- Although the interactions between vegeta- to change approximately simultaneously sky, 1990) by virtue of its origin in season- tion and climate are complex, they do during a period of glacial onset or ally dry parts of the tropics. conform to some general and recurrent deglaciation and global warming. The Glossopteris-dominated flora per- patterns that exist on different scales in When ecosystems are physically dis- sisted throughout the Permian and diversi- space and time. Recognizing patterns and rupted by short-term but severe and fied in complexity of leaf venation and principles of change at the icehouse-green- widespread perturbations, opportunists reproductive structures. In addition, tropi- house transitions of the late Paleozoic will will have a distinct advantage in securing cal plants appeared in the temperate areas enable us to use this understanding to and maintaining dominance. The low- in response to higher rainfall and due to make predictions about changes to come. land-wetland, tropical Late Pennsylvanian the drying of most of the tropical areas. (Stephanian) is, in some ways, analogous The temperate areas of Gondwana were ACKNOWLEDGMENTS to an extended “fern spike” recognized as clearly not very cold (Cuneo, 1987), cer- the initial recovery phase following the William L. Crepet, Louis Derry, tainly much warmer than hypothesized Cretaceous-Tertiary extinction event Robert W. Kay, and two anonymous by climate models (Yemane, 1993). This is (Nichols et al., 1986). reviewers offered helpful discussions and reflected in the successful colonization by
6 GSA TODAY, October 1996 review of the manuscript. We thank T. L. Dorofyeva, L. A., Davydov, V. I., and Kashlik, D. S., Nichols, D. J., Jarzen, D. M., Orth, C. J., and Oliver, 1982, Mode of temperature variation in the late Paleo- P. Q., 1986, Palynology and iridium anomalies at Creta- Phillips for granting permission to use the zoic of the southwest Darvaz: Akademie Nauk SSSR ceous-Tertiary boundary, south-central Saskatchewan: reconstruction of a Pennsylvanian peat Doklady, Earth Science Section, v. 263, p. 81–89. Science, v. 231, p. 714–717. swamp. This research has been supported Elias, M. K., 1936, Late Paleozoic plants of the Midcon- Niklas, K. J., Tiffney, B. H., and Knoll, A., 1983, Patterns by various funding agencies, including the tinent region as indicators of time and of environment: in vascular land plant diversification: Nature, v. 303, International Geological Congress, 16th, Compte p. 614–616. National Science Foundation to Gastaldo, Rendu, v. 1, p. 691–700. the American Chemical Society, the Pfefferkorn, H. W., 1995, We are temperate climate Erwin, D. H., 1996, The mother of mass extinctions: chauvinists: Palaios, v. 10, p. 389–391. Deutsches Forschung Gemeinschaft, the Scientific American, v. 275, p. 72–78. Pfefferkorn, H. W., and Thomson, M. C., 1982, Changes Research Foundation of the University of Fischer, A .G., 1982, Long-term climatic oscillations in dominance patterns in upper Carboniferous plant- Pennsylvania, and the Smithsonian Insti- recorded in stratigraphy, in Berger, W. H. and Crowell, fossil assemblages: Geology, v. 10, p. 641–644. J. C., eds., Climate in Earth history: Washington, D.C.: tution. Evolution of Terrestrial Ecosystem Phillips, T. L., and Cross, A. T., 1991, Paleobotany and National Academy Press, p. 97–104. Program contribution #30. paleoecology of coal, in Gluskoter, H. J., et al., eds., Frakes, L. A., Francis, J. E., and Syktus, J. 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L., 1995, The PUBLICATIONS OF RELATED INTEREST FROM GSA response of hierarchically structured ecosystems to Pangea: Paleoclimate, Tectonics, and Sedimentation during Accretion, Zenith, and Breakup of a long-term climate change: A case study using tropical peat swamps of Pennsylvanian age, in Stanley, S. M., et Supercontinent (SPE288, $72.50, Member price $58.00 al., eds., Effects of past global change on life: Washing- Economic Geology, U.S. (GNA-P2, $80.00, Member price $65.00) ton, D.C., National Academy Press, p. 134–155. Gondwana Master Basin of Peninsular India between Tethys and the Interior of the Gondwanaland DiMichele, W. A., and Phillips, T. 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