TY - JOUR

T1 - Uplands, lowlands, and climate

T2 - Taphonomic megabiases and the apparent rise of a xeromorphic, drought-tolerant flora during the Pennsylvanian-Permian transition

AU - DiMichele, William A.

AU - Bashforth, Arden R.

AU - Falcon-Lang, Howard J.

AU - Lucas, Spencer G.

PY - 2020

Y1 - 2020

N2 - The Late Mississippian and Pennsylvanian have been referred to as the Coal Age due to enormous paleotropical peat accumulations (coal beds). Numerous fossil floras have been collected from these coals, and their associated seat-earth paleosols and roof-shales, over more than two centuries, leading to the inference of vast swampy wetlands covering the Pangean tropics during the Pennsylvanian. In contrast, the Permian tropics are characterized as more arid, with sparser and more heterogeneous vegetation than inferred for the Pennsylvanian. In the tropics, the Pennsylvanian to Permian transition has been described as a changeover from a pteridophytedominated "Paleophytic flora", to a seed-plant dominated "Mesophytic flora. This view notwithstanding, floras dominated by xeromorphic seed plants also are well known from the Pennsylvanian tropics. Some authors have characterized these plants as being occupants of uplands, subsequently transported into basinal-lowland, preservational environments. In this model, uplands are well drained, causing areas of drought under otherwise everwet climates. In this paper, we present an alternative interpretation: that the apparent transition in Pennsylvanian-Permian tropical vegetation reflects two types of taphonomic megabias. First is a preservational megabias, strongly favoring the vegetation of humid climates over that of seasonally dry climates. Accordingly, tropical-plant preservational potential fluctuated in concert with Late Paleozoic Ice Age glacial-interglacial oscillations, and contemporaneous sea-level and climatic changes. Second is an analytical megabias, strongly favoring the discovery and collection of the wetland biome from Pennsylvanian strata, overlooking the less frequently and more poorly preserved drought-tolerant biome. By Permian times, vast wetlands, and their fossil record, had largely disappeared from central Pangea (although continuing in Cathaysia), making drought-tolerant vegetation more "visible" to searchers, without changing its preservational circumstances. We demonstrate that the upland model is untenable, being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record.

AB - The Late Mississippian and Pennsylvanian have been referred to as the Coal Age due to enormous paleotropical peat accumulations (coal beds). Numerous fossil floras have been collected from these coals, and their associated seat-earth paleosols and roof-shales, over more than two centuries, leading to the inference of vast swampy wetlands covering the Pangean tropics during the Pennsylvanian. In contrast, the Permian tropics are characterized as more arid, with sparser and more heterogeneous vegetation than inferred for the Pennsylvanian. In the tropics, the Pennsylvanian to Permian transition has been described as a changeover from a pteridophytedominated "Paleophytic flora", to a seed-plant dominated "Mesophytic flora. This view notwithstanding, floras dominated by xeromorphic seed plants also are well known from the Pennsylvanian tropics. Some authors have characterized these plants as being occupants of uplands, subsequently transported into basinal-lowland, preservational environments. In this model, uplands are well drained, causing areas of drought under otherwise everwet climates. In this paper, we present an alternative interpretation: that the apparent transition in Pennsylvanian-Permian tropical vegetation reflects two types of taphonomic megabias. First is a preservational megabias, strongly favoring the vegetation of humid climates over that of seasonally dry climates. Accordingly, tropical-plant preservational potential fluctuated in concert with Late Paleozoic Ice Age glacial-interglacial oscillations, and contemporaneous sea-level and climatic changes. Second is an analytical megabias, strongly favoring the discovery and collection of the wetland biome from Pennsylvanian strata, overlooking the less frequently and more poorly preserved drought-tolerant biome. By Permian times, vast wetlands, and their fossil record, had largely disappeared from central Pangea (although continuing in Cathaysia), making drought-tolerant vegetation more "visible" to searchers, without changing its preservational circumstances. We demonstrate that the upland model is untenable, being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record.

KW - Wetland

KW - Dryland

KW - Paleophytic

KW - Mesophytic

KW - Late Paleozoic

KW - CENTRAL APPALACHIAN BASIN

KW - TROPICAL RAIN-FOREST

KW - UPPER SILESIAN BASIN

KW - DESMOINESIAN-MISSOURIAN BOUNDARY

KW - PHYLOGENETIC NICHE CONSERVATISM

KW - WESTERN EQUATORIAL PANGEA

KW - INTRA-SUDETIC BASIN

KW - PALEOZOIC ICE-AGE

KW - LOWER CUTLER BEDS

KW - CONEMAUGH GROUP

U2 - 10.1016/j.palaeo.2020.109965

DO - 10.1016/j.palaeo.2020.109965

M3 - Journal article

VL - 559

JO - Palaeogeography, Palaeoclimatology, Palaeoecology - An International Journal for the Geo-Sciences

JF - Palaeogeography, Palaeoclimatology, Palaeoecology - An International Journal for the Geo-Sciences

SN - 0031-0182

M1 - 109965

ER -