Publications by authors named "William A DiMichele"

12 Publications

  • Page 1 of 1

Carboniferous plant physiology breaks the mold.

New Phytol 2020 08 8;227(3):667-679. Epub 2020 Apr 8.

Center for Integrative Geosciences, University of Connecticut, Storrs, CT, 06269, USA.

How plants have shaped Earth surface feedbacks over geologic time is a key question in botanical and geological inquiry. Recent work has suggested that biomes during the Carboniferous Period contained plants with extraordinary physiological capacity to shape their environment, contradicting the previously dominant view that plants only began to actively moderate the Earth's surface with the rise of angiosperms during the Mesozoic Era. A recently published Viewpoint disputes this recent work, thus here, we document in detail, the mechanistic underpinnings of our modeling and illustrate the extraordinary ecophysiological nature of Carboniferous plants.
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http://dx.doi.org/10.1111/nph.16460DOI Listing
August 2020

A hidden cradle of plant evolution in Permian tropical lowlands.

Science 2018 12;362(6421):1414-1416

Palaeobotany Research Group, Institute of Geology and Palaeontology, University of Münster, Münster, Germany.

The latitudinal biodiversity gradient today has deep roots in the evolutionary history of Earth's biota over geologic time. In the marine realm, earliest fossil occurrences at low latitudes reveal a tropical cradle for many animal groups. However, the terrestrial fossil record-especially from drier environments that are thought to drive evolutionary innovation-is sparse. We present mixed plant-fossil assemblages from Permian equatorial lowlands in present-day Jordan that harbor precocious records of three major seed-plant lineages that all became dominant during the Mesozoic, including the oldest representative of any living conifer family. These finds offer a glimpse of the early evolutionary origins of modern plant groups in disturbance-prone tropical habitats that are usually hidden from observation.
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http://dx.doi.org/10.1126/science.aau4061DOI Listing
December 2018

Fast or slow for the arborescent lycopsids?: Response to Thomas & Cleal (2018) 'Arborescent lycophyte growth in the late Carboniferous coal swamps'.

New Phytol 2018 05 19;218(3):891-893. Epub 2018 Feb 19.

Paleobiology, NMNH Smithsonian Institution, Washington, DC, 20560, USA.

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http://dx.doi.org/10.1111/nph.15059DOI Listing
May 2018

Dynamic Carboniferous tropical forests: new views of plant function and potential for physiological forcing of climate.

New Phytol 2017 Sep 25;215(4):1333-1353. Epub 2017 Jul 25.

Center for Integrative Geosciences, University of Connecticut, Storrs, CT, 06269, USA.

Contents 1333 I. 1334 II. 1335 III. 1339 IV. 1344 V. 1347 VI. 1347 1348 1348 References 1348 SUMMARY: The Carboniferous, the time of Earth's penultimate icehouse and widespread coal formation, was dominated by extinct lineages of early-diverging vascular plants. Studies of nearest living relatives of key Carboniferous plants suggest that their physiologies and growth forms differed substantially from most types of modern vegetation, particularly forests. It remains a matter of debate precisely how differently and to what degree these long-extinct plants influenced the environment. Integrating biophysical analysis of stomatal and vascular conductivity with geochemical analysis of fossilized tissues and process-based ecosystem-scale modeling yields a dynamic and unique perspective on these paleoforests. This integrated approach indicates that key Carboniferous plants were capable of growth and transpiration rates that approach values found in extant crown-group angiosperms, differing greatly from comparatively modest rates found in their closest living relatives. Ecosystem modeling suggests that divergent stomatal conductance, leaf sizes and stem life span between dominant clades would have shifted the balance of soil-atmosphere water fluxes, and thus surface runoff flux, during repeated, climate-driven, vegetation turnovers. This synthesis highlights the importance of 'whole plant' physiological reconstruction of extinct plants and the potential of vascular plants to have influenced the Earth system hundreds of millions of years ago through vegetation-climate feedbacks.
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http://dx.doi.org/10.1111/nph.14700DOI Listing
September 2017

Delayed fungal evolution did not cause the Paleozoic peak in coal production.

Proc Natl Acad Sci U S A 2016 Mar 19;113(9):2442-7. Epub 2016 Jan 19.

Geological Sciences, Stanford University, Stanford, CA 94305;

Organic carbon burial plays a critical role in Earth systems, influencing atmospheric O2 and CO2 concentrations and, thereby, climate. The Carboniferous Period of the Paleozoic is so named for massive, widespread coal deposits. A widely accepted explanation for this peak in coal production is a temporal lag between the evolution of abundant lignin production in woody plants and the subsequent evolution of lignin-degrading Agaricomycetes fungi, resulting in a period when vast amounts of lignin-rich plant material accumulated. Here, we reject this evolutionary lag hypothesis, based on assessment of phylogenomic, geochemical, paleontological, and stratigraphic evidence. Lignin-degrading Agaricomycetes may have been present before the Carboniferous, and lignin degradation was likely never restricted to them and their class II peroxidases, because lignin modification is known to occur via other enzymatic mechanisms in other fungal and bacterial lineages. Furthermore, a large proportion of Carboniferous coal horizons are dominated by unlignified lycopsid periderm with equivalent coal accumulation rates continuing through several transitions between floral dominance by lignin-poor lycopsids and lignin-rich tree ferns and seed plants. Thus, biochemical composition had little relevance to coal accumulation. Throughout the fossil record, evidence of decay is pervasive in all organic matter exposed subaerially during deposition, and high coal accumulation rates have continued to the present wherever environmental conditions permit. Rather than a consequence of a temporal decoupling of evolutionary innovations between fungi and plants, Paleozoic coal abundance was likely the result of a unique combination of everwet tropical conditions and extensive depositional systems during the assembly of Pangea.
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http://dx.doi.org/10.1073/pnas.1517943113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780611PMC
March 2016

Holocene shifts in the assembly of plant and animal communities implicate human impacts.

Nature 2016 Jan 16;529(7584):80-3. Epub 2015 Dec 16.

Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.

Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.
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http://dx.doi.org/10.1038/nature16447DOI Listing
January 2016

Conservatism of Late Pennsylvanian vegetational patterns during short-term cyclic and long-term directional environmental change, western equatorial Pangea.

Geol Soc Spec Publ 2013 Sep;376(1):201-234

Department of Paleobiology, NMNH Smithsonian Institution, Washington, DC 20560, USA.

Patterns of plant distribution by palaeoenvironment were examined across the Pennsylvanian-Permian transition in North-Central Texas. Stratigraphically recurrent packages of distinct lithofacies, representing different habitats, contain qualitatively and quantitatively different macrofloras and microfloras. The species pools demonstrate niche conservatism, remaining closely tied to specific habitats, during both short-term cyclic environmental change and a long-term trend of increasing aridity. The deposits examined principally comprise the terrestrial Markley and its approximate marine equivalent, the Harpersville Formation and parts of lower Archer City Formation. Fossiliferous deposits are lens-like, likely representing fill sequences of channels formed during abandonment phases. Palaeosols, represented by blocky mudstones, comprise a large fraction of the deposits. They suggest progressive climate change from minimally seasonal humid to seasonal subhumid to seasonal dry subhumid. Five lithofacies yielded plants: kaolinite-dominated siltstone, organic shale, mudstone beds within organic shale, coarsening upward mudstone-sandstone interbeds and channel sandstone. Both macro- and microflora were examined. Lithofacies proved compositionally distinct, with different patterns of dominance diversity. Organic shales (swamp deposits), mudstone partings (swamp drainages) and coarsening upward mudstone-sandstone interbeds (floodplains) typically contain Pennsylvanian wetland vegetation. Kaolinite-dominated siltstones and (to the extent known) sandstones contain taxa indicative of seasonally dry substrates. Some kaolinite-dominated siltstones and organic shales/coals yielded palynomorphs. Microfloras are more diverse, with greater wetland-dryland overlap than macrofloras. It appears that these two floras were coexistent at times on the regional landscape.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4203347PMC
http://dx.doi.org/10.1144/sp376.14DOI Listing
September 2013

Growth habit of the late Paleozoic rhizomorphic tree-lycopsid family Diaphorodendraceae: phylogenetic, evolutionary, and paleoecological significance.

Am J Bot 2013 Aug 8;100(8):1604-25. Epub 2013 Aug 8.

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA.

Premise Of The Study: Rhizomorphic lycopsids evolved the tree habit independently of all other land plants. Newly discovered specimens allow radical revision of our understanding of the growth architectures of the extinct Paleozoic sister-genera Synchysidendron and Diaphorodendron.

Methods: Detailed descriptions of six remarkable adpression specimens from the Pennsylvanian of the USA and three casts from the late Mississippian of Scotland are used to revise and reanalyze a previously published morphological cladistic matrix and to reinterpret their remarkable growth forms.

Key Results: Contrary to previous assertions, Synchysidendron resembled Diaphorodendron in having a distinct and relatively complex growth habit that emphasized serially homologous, closely spaced, deciduous lateral branches at the expense of reduced monocarpic crown branches. Lateral branches originated through several strongly anisotomous dichotomies before producing during extended periods large numbers of Achlamydocarpon strobili. The comparatively large diameter of abscission scars remaining on the main trunk and the emergence of branches above the horizontal plane suggest that the lateral branch systems were robust. Lateral branches were borne in two opposite rows on the main trunk and continued upward into an isotomously branched, determinate crown; their striking distichous arrangement caused preferred orientation of fallen trunks on bedding planes.

Conclusions: This discovery identifies the plagiotropic growth habit, dominated by serial lateral branches, as ubiquitous in the Diaphorodendraceae and also as unequivocally primitive within Isoetales s.l., a conclusion supported by both the revised morphological cladistic analysis and relative first appearances of taxa in the fossil record. Previously assumed complete homology between crown branching in Lepidodendraceae and that of all earlier-divergent genera requires reassessment. Saltational phenotypic transitions via modification of key developmental switches remains the most credible explanation for architectural evolution in the group. The resulting architecture allowed Diaphorodendraceae to co-dominate disturbed, clastic, equatorial wetlands from the Asbian to the Early Permian.
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http://dx.doi.org/10.3732/ajb.1200623DOI Listing
August 2013

Permian Coal Forest offers a glimpse of late Paleozoic ecology.

Proc Natl Acad Sci U S A 2012 Mar 15;109(13):4717-8. Epub 2012 Mar 15.

Department of Paleobiology, National Museum of Natural History Smithsonian Institution, Washington, DC 20560, USA.

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http://dx.doi.org/10.1073/pnas.1203261109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3324014PMC
March 2012

CO2-forced climate and vegetation instability during Late Paleozoic deglaciation.

Science 2007 Jan;315(5808):87-91

Department of Geology, University of California, Davis, CA 95616, USA.

The late Paleozoic deglaciation is the vegetated Earth's only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO2) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO2, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO2 shifts, illustrating the biotic impact associated with past CO2-forced turnover to a permanent ice-free world.
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http://dx.doi.org/10.1126/science.1134207DOI Listing
January 2007

THE PENNSYLVANIAN-PERMIAN VEGETATIONAL TRANSITION: A TERRESTRIAL ANALOGUE TO THE ONSHORE-OFFSHORE HYPOTHESIS.

Evolution 1992 Jun;46(3):807-824

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA.

An analysis of 68 floras from the Pennsylvanian and Early Permian of Euramerica reveals distinct patterns of environmental distribution. Wetland assemblages are the most commonly encountered floras from the Early and Middle Pennsylvanian. Floras from drier habitats characterize the Permian. Both wetland and dry-site floras occur in the Late Pennsylvanian, but floristic overlap is minimal, which implies strong environmental controls on the distributions of the component species. Drier habitats appear to be the sites of first appearance of orders that become prominent during the Late Permian and Mesozoic. Higher taxa originated in physically heterogeneous, drier habitats, which were geographically marginal throughout most of the Pennsylvanian. They then moved into the lowlands during periods of climatic drying in the Permian, replacing older wetland vegetation. This pattern is analogous to the marine onshore-offshore pattern of origination and migration. The derivation of Mesozoic wetland clades from the Permian dry-lowland vegetation completes the parallel. The similarities of the marine and terrestrial patterns suggest that the combination of evolutionary opportunity, created by physical heterogeneity of the environment, and migrational opportunity, created by changing extrinsic conditions, may be underlying factors that transcend the specifics of organism and environment.
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http://dx.doi.org/10.1111/j.1558-5646.1992.tb02086.xDOI Listing
June 1992