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      Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways

      1 , 2 , * , 3 , 4

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          Abstract

          We report the discovery of two very early, basal-amniote fossil trackways on the same bedding plane in eolian sandstone of the Pennsylvanian Manakacha Formation in Grand Canyon, Arizona. Trackway 1, which is Chelichnus-like, we interpret to be a shallow undertrackway. It displays a distinctive, sideways-drifting, footprint pattern not previously documented in a tetrapod trackway. We interpret this pattern to record the trackmaker employing a lateral-sequence gait while diagonally ascending a slope of about 20°, thereby reducing the steepness of the ascent. Trackway 2 consists only of aligned sets of claw marks. We interpret this trackway to be a deeper undertrackway, made some hours or days later, possibly by an animal that was conspecific with Trackmaker 1, while walking directly up the slope at a speed of approximately 0.1 m/sec. These trackways are the first tetrapod tracks reported from the Manakacha Formation and the oldest in the Grand Canyon region. The narrow width of both trackways indicates that both trackmakers had relatively small femoral abduction angles and correspondingly relatively erect postures. They represent the earliest known occurrence of dunefield-dwelling amniotes―either basal reptiles or basal synapsids―thereby extending the known utilization of the desert biome by amniotes, as well as the presence of the Chelichnus ichnofacies, by at least eight million years, into the Atokan/Moscovian Age of the Pennsylvanian Epoch. The depositional setting was a coastal-plain, eolian dunefield in which tidal or wadi flooding episodically interrupted eolian processes and buried the dunes in mud.

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          Most cited references 75

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          A reevaluation of early amniote phylogeny

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            A chronology of Paleozoic sea-level changes.

            Sea levels have been determined for most of the Paleozoic Era (542 to 251 million years ago), but an integrated history of sea levels has remained unrealized. We reconstructed a history of sea-level fluctuations for the entire Paleozoic by using stratigraphic sections from pericratonic and cratonic basins. Evaluation of the timing and amplitude of individual sea-level events reveals that the magnitude of change is the most problematic to estimate accurately. The long-term sea level shows a gradual rise through the Cambrian, reaching a zenith in the Late Ordovician, then a short-lived but prominent withdrawal in response to Hirnantian glaciation. Subsequent but decreasingly substantial eustatic highs occurred in the mid-Silurian, near the Middle/Late Devonian boundary, and in the latest Carboniferous. Eustatic lows are recorded in the early Devonian, near the Mississippian/Pennsylvanian boundary, and in the Late Permian. One hundred and seventy-two eustatic events are documented for the Paleozoic, varying in magnitude from a few tens of meters to approximately 125 meters.
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              Basic types of stratification in small eolian dunes

               RALPH HUNTER (1977)
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: InvestigationRole: MethodologyRole: Project administrationRole: SupervisionRole: Writing – original draftRole: Writing – review & editing
                Role: Data curationRole: InvestigationRole: MethodologyRole: Writing – review & editing
                Role: Formal analysisRole: MethodologyRole: Software
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                19 August 2020
                2020
                : 15
                : 8
                Affiliations
                [1 ] Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada, United States of America
                [2 ] Las Vegas Natural History Museum, Las Vegas, Nevada, United States of America
                [3 ] Pacific Section SEPM (Society for Sedimentary Geology), Tujunga, California, United States of America
                [4 ] Department of Physical Sciences, College of Southern Nevada, Las Vegas, Nevada, United States of America
                University of Wisconsin Madison, UNITED STATES
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Article
                PONE-D-19-29394
                10.1371/journal.pone.0237636
                7437920
                32813715
                © 2020 Rowland et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Figures: 14, Tables: 0, Pages: 28
                Product
                Funding
                The publication fees for this article were generously supported by the UNLV University Libraries Open Article Fund.
                Categories
                Research Article
                Biology and Life Sciences
                Organisms
                Eukaryota
                Animals
                Vertebrates
                Amniotes
                Biology and Life Sciences
                Zoology
                Animals
                Vertebrates
                Amniotes
                Biology and Life Sciences
                Physiology
                Biological Locomotion
                Earth Sciences
                Geology
                Stratigraphy
                Biology and Life Sciences
                Physiology
                Biological Locomotion
                Walking
                Earth Sciences
                Geology
                Geologic Time
                Paleozoic Era
                Permian Period
                Biology and Life Sciences
                Anatomy
                Body Limbs
                Legs
                Feet
                Medicine and Health Sciences
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                Feet
                Biology and Life Sciences
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                Eukaryota
                Animals
                Prehistoric Animals
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                Zoology
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                Paleontology
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                Archosauria
                Dinosaurs
                Earth Sciences
                Paleontology
                Prehistoric Animals
                Archosauria
                Dinosaurs
                Biology and Life Sciences
                Paleontology
                Paleobiology
                Paleozoology
                Vertebrate Paleontology
                Prehistoric Animals
                Archosauria
                Dinosaurs
                Earth Sciences
                Paleontology
                Paleobiology
                Paleozoology
                Vertebrate Paleontology
                Prehistoric Animals
                Archosauria
                Dinosaurs
                Biology and Life Sciences
                Organisms
                Eukaryota
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