Collaborative Research: Macrophytes Across the Proterozoic - Phanerozoic Boundary: A Baseline Study of Macroalgae During a Critical Interval in Earth System History

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Collaborative Research: Macrophytes Across the Proterozoic - Phanerozoic Boundary: A Baseline Study of Macroalgae During a Critical Interval in Earth System HistorySteven LoDuca and Shuhai XiaoEastern Michigan University and Virginia Tech UniversityBenthic macroalgae in present-day shallow marine ecosystems play a critical role in primary production and habitat provision, sediment generation, transportation, and accumulation, and organic carbon burial. In a broader Earth system context, they play a key role in the dynamics of the global carbon cycle and carbon isotope variations. Fossil data indicate that macroalgae originated during the early Proterozoic, but little is known about them across the Proterozoic-Phanerozoic boundary and into the early Paleozoic. Yet, it is likely that macroalgae during this critical interval played an even larger role in Biosphere and Earth system dynamics than today because of the confluence of three factors: (1) widespread epeiric seas, (2) lack of other marine macrophytes (seagrasses are Mesozoic in origin), and (3) the occurrence of major animal diversification events during the Ediacaran-Cambrian transition and in the Ordovician, which were focused within shallow marine settings. Our lack of information about macroalgae during this timeframe, therefore, amounts to a serious knowledge gap. This project will use the fossil record of macroalgae, particularly noncalcified forms represented abundantly in Ediacaran and early Paleozoic Konservat-Lagerstätten, to begin to fill this gap. Specifically, this will be accomplished through a multidisciplinary, four-pronged approach: (1) Integrative Analysis and Identification of problematic nonmineralized taxa with gross morphologies permissive of both algal and animal affinities, including species from the Lantian (Ediacaran), Burgess Shale, Chengjiang, and Kaili biotas; (2) Morphospace Characterization, including morphometric analyses of morphospace occupation, canopy heights, and thallus surface area to volume ratios; (3) Paleoecological Characterization, including comparisons with modern macroalgal communities; and (4) Stable Carbon Isotope Investigation of carbonate, total organic carbon, and individual macroalgal fossils, focusing on stratigraphic intervals known to yield an abundance of noncalcified macroalgae and to host significant carbon isotope variations. Key questions to be addressed during this investigation include: Did macroalgae experience significant episodes of morphological diversification concomitant with the Cambrian Explosion and Ordovician Radiation (GOBE) events? How do early Paleozoic macroalgal communities compare with those of Ediacaran and modern seas? Did the full array of macroalgal functional-form groups known from modern seas exist by the end of the early Paleozoic? Did massive influxes of nutrients caused by the initial colonization of the land by terrestrial plants trigger colossal blooms of macroalgae in early Paleozoic seas, and could such blooms have contributed to organic carbon burial thus driving major carbon isotope excursions identified in the early Paleozoic sedimentary rock record? This baseline study will establish the foundation necessary for larger-scale investigations of the Earth-Life system during this critical interval, including evolutionary feedback between early marine animals and algae and changing carbon cycle dynamics. The broader impacts of this project are realized, in part, through numerous educational dimensions built into the work, including training for graduate and undergraduate students and public outreach efforts to assist training of K-12 teachers through existing STEM programs. This project also involves international collaborations with Chinese and Canadian paleontologists. Directly related to the project, a website, entitled "Prehistoric Marine Flora," will be constructed and linked to the Paleontology Portal to promote the importance of this work to the general public. In addition, the taxonomic data generated by this project will be uploaded to the Paleobiology Database, and all fossil specimens will be reposited in publicly accessible museums. Finally, in terms of broader benefit to society, this research forms an important part of our quest to understand the origins of our biodiversity. The deep past is part of our collective human heritage, and a better understanding of our origins enriches us all.