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Anderson RP, Mughal S, Wedlake GO. Proterozoic microfossils continue to provide new insights into the rise of complex eukaryotic life. ROYAL SOCIETY OPEN SCIENCE 2024; 11:240154. [PMID: 39170929 PMCID: PMC11336685 DOI: 10.1098/rsos.240154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 07/11/2024] [Accepted: 07/12/2024] [Indexed: 08/23/2024]
Abstract
Eukaryotes have evolved to dominate the biosphere today, accounting for most documented living species and the vast majority of the Earth's biomass. Consequently, understanding how these biologically complex organisms initially diversified in the Proterozoic Eon over 539 million years ago is a foundational question in evolutionary biology. Over the last 70 years, palaeontologists have sought to document the rise of eukaryotes with fossil evidence. However, the delicate and microscopic nature of their sub-cellular features affords early eukaryotes diminished preservation potential. Chemical biomarker signatures of eukaryotes and the genetics of living eukaryotes have emerged as complementary tools for reconstructing eukaryote ancestry. In this review, we argue that exceptionally preserved Proterozoic microfossils are critical to interpreting these complementary tools, providing crucial calibrations to molecular clocks and testing hypotheses of palaeoecology. We highlight recent research on their preservation and biomolecular composition that offers new ways to enhance their utility.
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Affiliation(s)
- Ross P. Anderson
- Museum of Natural History, University of Oxford, OxfordOX1 3PW, UK
- All Souls College, University of Oxford, OxfordOX1 4AL, UK
| | - Sanaa Mughal
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AlbertaT6G 2E3, Canada
| | - George O. Wedlake
- Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK
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2
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Porfirio-Sousa AL, Tice AK, Morais L, Ribeiro GM, Blandenier Q, Dumack K, Eglit Y, Fry NW, Gomes E Souza MB, Henderson TC, Kleitz-Singleton F, Singer D, Brown MW, Lahr DJG. Amoebozoan testate amoebae illuminate the diversity of heterotrophs and the complexity of ecosystems throughout geological time. Proc Natl Acad Sci U S A 2024; 121:e2319628121. [PMID: 39012821 PMCID: PMC11287125 DOI: 10.1073/pnas.2319628121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Accepted: 06/01/2024] [Indexed: 07/18/2024] Open
Abstract
Heterotrophic protists are vital in Earth's ecosystems, influencing carbon and nutrient cycles and occupying key positions in food webs as microbial predators. Fossils and molecular data suggest the emergence of predatory microeukaryotes and the transition to a eukaryote-rich marine environment by 800 million years ago (Ma). Neoproterozoic vase-shaped microfossils (VSMs) linked to Arcellinida testate amoebae represent the oldest evidence of heterotrophic microeukaryotes. This study explores the phylogenetic relationship and divergence times of modern Arcellinida and related taxa using a relaxed molecular clock approach. We estimate the origin of nodes leading to extant members of the Arcellinida Order to have happened during the latest Mesoproterozoic and Neoproterozoic (1054 to 661 Ma), while the divergence of extant infraorders postdates the Silurian. Our results demonstrate that at least one major heterotrophic eukaryote lineage originated during the Neoproterozoic. A putative radiation of eukaryotic groups (e.g., Arcellinida) during the early-Neoproterozoic sustained by favorable ecological and environmental conditions may have contributed to eukaryotic life endurance during the Cryogenian severe ice ages. Moreover, we infer that Arcellinida most likely already inhabited terrestrial habitats during the Neoproterozoic, coexisting with terrestrial Fungi and green algae, before land plant radiation. The most recent extant Arcellinida groups diverged during the Silurian Period, alongside other taxa within Fungi and flowering plants. These findings shed light on heterotrophic microeukaryotes' evolutionary history and ecological significance in Earth's ecosystems, using testate amoebae as a proxy.
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Affiliation(s)
- Alfredo L. Porfirio-Sousa
- Department of Zoology, Institute of Biosciences, University of São Paulo, São Paulo05508-090, Brazil
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
| | - Alexander K. Tice
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
- Department of Biological Sciences, Texas Tech University, Lubbock, TX79409
| | - Luana Morais
- Department of Geophysics, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo05508-090, Brazil
- Department of Applied Geology, Institute of Geosciences and Exact Sciences, São Paulo State University, Rio Claro13506-900, Brazil
| | - Giulia M. Ribeiro
- Department of Zoology, Institute of Biosciences, University of São Paulo, São Paulo05508-090, Brazil
| | - Quentin Blandenier
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
| | - Kenneth Dumack
- Department of Terrestrial Ecology, Institute of Zoology, University of Cologne, Cologne50674, Germany
| | - Yana Eglit
- Department of Biology, Dalhousie University, Halifax, NSB3H 4R2, Canada
- Department of Biology, Institute for Comparative Genomics, Dalhousie University, Halifax, NSV8P 3E6, Canada
- Department of Biology, University of Victoria, Victoria, BCV8P 3E6, Canada
| | - Nicholas W. Fry
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
| | | | - Tristan C. Henderson
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
| | | | - David Singer
- Soil Science and Environment Group, Changins, Haute école spécialisée de Suisse occidentale University of Applied Sciences and Arts Western Switzerland, Nyon1148, Switzerland
| | - Matthew W. Brown
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS39762
- Department of Biological Sciences, Institute for Genomics, Biocomputing & Biotechnology, Mississippi State University, Mississippi State, MS39762
| | - Daniel J. G. Lahr
- Department of Zoology, Institute of Biosciences, University of São Paulo, São Paulo05508-090, Brazil
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Yu Y, Li YP, Ren K, Hao X, Fru EC, Rønn R, Rivera WL, Becker K, Feng R, Yang J, Rensing C. A brief history of metal recruitment in protozoan predation. Trends Microbiol 2024; 32:465-476. [PMID: 38103995 DOI: 10.1016/j.tim.2023.11.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 11/20/2023] [Accepted: 11/23/2023] [Indexed: 12/19/2023]
Abstract
Metals and metalloids are used as weapons for predatory feeding by unicellular eukaryotes on prokaryotes. This review emphasizes the role of metal(loid) bioavailability over the course of Earth's history, coupled with eukaryogenesis and the evolution of the mitochondrion to trace the emergence and use of the metal(loid) prey-killing phagosome as a feeding strategy. Members of the genera Acanthamoeba and Dictyostelium use metals such as zinc (Zn) and copper (Cu), and possibly metalloids, to kill their bacterial prey after phagocytosis. We provide a potential timeline on when these capacities first evolved and how they correlate with perceived changes in metal(loid) bioavailability through Earth's history. The origin of phagotrophic eukaryotes must have postdated the Great Oxidation Event (GOE) in agreement with redox-dependent modification of metal(loid) bioavailability for phagotrophic poisoning. However, this predatory mechanism is predicted to have evolved much later - closer to the origin of the multicellular metazoans and the evolutionary development of the immune systems.
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Affiliation(s)
- Yanshuang Yu
- Institute of Environmental Microbiology, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Yuan-Ping Li
- Institute of Environmental Microbiology, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Kexin Ren
- Aquatic EcoHealth Group, Fujian Key Laboratory of Watershed Ecology, Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
| | - Xiuli Hao
- Hubei Key Laboratory of Soil Environment and Pollution Remediation, Huazhong Agricultural University, Wuhan 430070, China
| | - Ernest Chi Fru
- Centre for Geobiology and Geochemistry, School of Earth and Ocean Sciences, Cardiff University, CF10 3AT Cardiff, UK
| | - Regin Rønn
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Windell L Rivera
- Pathogen-Host-Environment Interactions Research Laboratory, Institute of Biology, College of Science, University of the Philippines Diliman, Quezon City 1101, Philippines
| | - Karsten Becker
- Friedrich Loeffler-Institute for Medical Microbiology, University Medicine Greifswald, D-17489 Greifswald, Germany
| | - Renwei Feng
- Institute of Environmental Microbiology, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China
| | - Jun Yang
- Aquatic EcoHealth Group, Fujian Key Laboratory of Watershed Ecology, Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
| | - Christopher Rensing
- Institute of Environmental Microbiology, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, Fujian 350002, China.
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Abstract
The origin of modern eukaryotes is one of the key transitions in life's history, and also one of the least understood. Although the fossil record provides the most direct view of this process, interpreting the fossils of early eukaryotes and eukaryote-grade organisms is not straightforward. We present two end-member models for the evolution of modern (i.e., crown) eukaryotes-one in which modern eukaryotes evolved early, and another in which they evolved late-and interpret key fossils within these frameworks, including where they might fit in eukaryote phylogeny and what they may tell us about the evolution of eukaryotic cell biology and ecology. Each model has different implications for understanding the rise of complex life on Earth, including different roles of Earth surface oxygenation, and makes different predictions that future paleontological studies can test.
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Affiliation(s)
- Susannah M Porter
- Department of Earth Science, University of California at Santa Barbara, Santa Barbara, California, USA;
| | - Leigh Anne Riedman
- Department of Earth Science, University of California at Santa Barbara, Santa Barbara, California, USA;
- Earth Research Institute, University of California at Santa Barbara, Santa Barbara, California, USA;
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Wang K, Xu HH, Liu BC, Bai J, Wang Y, Tang P, Lu JF, Wang Y. Shallow-marine testate amoebae with internal structures from the Lower Devonian of China. iScience 2023; 26:106678. [PMID: 37182111 PMCID: PMC10173733 DOI: 10.1016/j.isci.2023.106678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 03/08/2023] [Accepted: 04/12/2023] [Indexed: 05/16/2023] Open
Abstract
Testate amoebae, a polyphyletic protist group inhabiting a wide variety of extant ecosystems, have evolved as far back as early Neoproterozoic. However, their fossil record is discontinuous and biased toward empty shells. Here, we report an arcellinid testate amoeba species, Cangwuella ampulliformis gen. nov., sp. nov., from a shallow-marine community in the Early Devonian of Guangxi, southwestern China. With the aid of scanning electron microscopy and X-ray micro-tomography, we find that the shell of our testate amoeba contains some acetabuliform structures. Although such configuration does not match exactly with the known internal structures in extant testate amoebae, our fossils highlight the potential of exploring the ecological relationships between fossil testate amoebae and their associated organisms, and increase our knowledge on the diversity of testate amoebae in Early Devonian environments.
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Affiliation(s)
- Kai Wang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hong-He Xu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- Corresponding author
| | - Bing-Cai Liu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jiao Bai
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yao Wang
- School of Geography and Tourism, Qufu Normal University, Rizhao 276826, China
| | - Peng Tang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
| | - Jian-Feng Lu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
| | - Yi Wang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, China
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Tingle KE, Porter SM, Raven MR, Czaja AD, Webb SM, Bloeser B. Organic preservation of vase-shaped microfossils from the late Tonian Chuar Group, Grand Canyon, Arizona, USA. GEOBIOLOGY 2023; 21:290-309. [PMID: 36651474 DOI: 10.1111/gbi.12544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2022] [Revised: 12/08/2022] [Accepted: 01/05/2023] [Indexed: 06/17/2023]
Abstract
Vase-shaped microfossils (VSMs) are found globally in middle Neoproterozoic (800-730 Ma) marine strata and represent the earliest evidence for testate (shell-forming) amoebozoans. VSM tests are hypothesized to have been originally organic in life but are most commonly preserved as secondary mineralized casts and molds. A few reports, however, suggest possible organic preservation. Here, we test the hypothesis that VSMs from shales of the lower Walcott Member of the Chuar Group, Grand Canyon, Arizona, contain original organic material, as reported by B. Bloeser in her pioneering studies of Chuar VSMs. We identified VSMs from two thin section samples of Walcott Member black shales in transmitted light microscopy and used scanning electron microscopy to image VSMs. Carbonaceous material is found within the internal cavity of all VSM tests from both samples and is interpreted as bitumen mobilized from Walcott shales likely during the Cretaceous. Energy dispersive X-ray spectroscopy (EDS) and wavelength dispersive X-ray spectroscopy (WDS) reveal that VSM test walls contain mostly carbon, iron, and sulfur, while silica is present only in the surrounding matrix. Raman spectroscopy was used to compare the thermal maturity of carbonaceous material within the samples and indicated the presence of pyrite and jarosite within fossil material. X-ray absorption spectroscopy revealed the presence of reduced organic sulfur species within the carbonaceous test walls, the carbonaceous material found within test cavities, and in the sedimentary matrix, suggesting that organic matter sulfurization occurred within the Walcott shales. Our suite of spectroscopic analyses reveals that Walcott VSM test walls are organic and sometimes secondarily pyritized (with the pyrite variably oxidized to jarosite). Both preservation modes can occur at a millimeter spatial scale within sample material, and at times even within a single specimen. We propose that sulfurization within the Walcott Shales promoted organic preservation, and furthermore, the ratio of iron to labile VSM organic material controlled the extent of pyrite replacement. Based on our evidence, we conclude that the VSMs are preserved with original organic test material, and speculate that organic VSMs may often go unrecognized, given their light-colored, translucent appearance in transmitted light.
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Affiliation(s)
- Kelly E Tingle
- Department of Earth Science, University of California, Santa Barbara, California, USA
| | - Susannah M Porter
- Department of Earth Science, University of California, Santa Barbara, California, USA
| | - Morgan R Raven
- Department of Earth Science, University of California, Santa Barbara, California, USA
| | - Andrew D Czaja
- Department of Geology, University of Cincinnati, Cincinnati, Ohio, USA
| | - Samuel M Webb
- Stanford Synchrotron Radiation Lightsource, Stanford University, Menlo Park, California, USA
| | - Bonnie Bloeser
- Department of Geological Sciences, San Diego State University, San Diego, California, USA
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7
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Li G, Chen L, Pang K, Tang Q, Wu C, Yuan X, Zhou C, Xiao S. Tonian carbonaceous compressions indicate that Horodyskia is one of the oldest multicellular and coenocytic macro-organisms. Commun Biol 2023; 6:399. [PMID: 37046079 PMCID: PMC10097871 DOI: 10.1038/s42003-023-04740-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Accepted: 03/21/2023] [Indexed: 04/14/2023] Open
Abstract
Macrofossils with unambiguous biogenic origin and predating the one-billion-year-old multicellular fossils Bangiomorpha and Proterocladus interpreted as crown-group eukaryotes are quite rare. Horodyskia is one of these few macrofossils, and it extends from the early Mesoproterozoic Era to the terminal Ediacaran Period. The biological interpretation of this enigmatic fossil, however, has been a matter of controversy since its discovery in 1982, largely because there was no evidence for the preservation of organic walls. Here we report new carbonaceous compressions of Horodyskia from the Tonian successions (~950-720 Ma) in North China. The macrofossils herein with bona fide organic walls reinforce the biogenicity of Horodyskia. Aided by the new material, we reconstruct Horodyskia as a colonial organism composed of a chain of organic-walled vesicles that likely represent multinucleated (coenocytic) cells of early eukaryotes. Two species of Horodyskia are differentiated on the basis of vesicle sizes, and their co-existence in the Tonian assemblage provides a link between the Mesoproterozoic (H. moniliformis) and the Ediacaran (H. minor) species. Our study thus provides evidence that eukaryotes have acquired macroscopic size through the combination of coenocytism and colonial multicellularity at least ~1.48 Ga, and highlights an exceptionally long range and morphological stasis of this Proterozoic macrofossils.
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Affiliation(s)
- Guangjin Li
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China
| | - Lei Chen
- College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao, 266590, China.
| | - Ke Pang
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China.
- University of Chinese Academy of Sciences, Beijing, 100049, China.
- University of Chinese Academy of Sciences, Nanjing, 211135, China.
| | - Qing Tang
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China
- Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Chengxi Wu
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xunlai Yuan
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Chuanming Zhou
- State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences, Nanjing, 210008, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
- University of Chinese Academy of Sciences, Nanjing, 211135, China
| | - Shuhai Xiao
- Department of Geosciences and Global Change Center, Virginia Tech, Blacksburg, VA, 24061, USA
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Lahr DJ. An emerging paradigm for the origin and evolution of shelled amoebae, integrating advances from molecular phylogenetics, morphology and paleontology. Mem Inst Oswaldo Cruz 2021; 116:e200620. [PMID: 34406221 PMCID: PMC8370470 DOI: 10.1590/0074-02760200620] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 07/05/2021] [Indexed: 11/22/2022] Open
Abstract
The phylogenetic paradigm of eukaryotic evolution has changed dramatically over the past two decades, with profound reflections on the understanding of life on earth. Arcellinida testate (shelled) amoebae lineages represent some of the oldest fossils of eukaryotes, and the elucidation of their phylogenetic relationships opened a window to the distant past, with important implications for understanding the evolution of life on earth. This four-part essay summarises advances made in the past 20 years regarding: (i) the phylogenetic relationships among amoebae with shells evolving in concert with the advances made in the phylogeny of eukaryotes; (ii) paleobiological studies unraveling the biological affinities of Neoproterozoic vase-shaped microfossils (VSMs); (iii) the interwoven interpretation of these different sets of data concluding that the Neoproterozoic contains a surprising diversity of organisms, in turn demanding a reinterpretation of the most profound events we know in the history of eukaryotes, and; (iv) a synthesis of the current knowledge about the evolution of Arcellinida, together with the possibilities and pitfalls of their interpretation.
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Affiliation(s)
- Daniel Jg Lahr
- Universidade de São Paulo, Instituto de Biociências, Departamento de Zoologia, São Paulo, SP, Brasil
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Riedman LA, Porter SM, Czaja AD. Phosphatic scales in vase-shaped microfossil assemblages from Death Valley, Grand Canyon, Tasmania, and Svalbard. GEOBIOLOGY 2021; 19:364-375. [PMID: 33634584 DOI: 10.1111/gbi.12439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 02/09/2021] [Accepted: 02/14/2021] [Indexed: 06/12/2023]
Abstract
Although biomineralized skeletal elements dominate the Phanerozoic fossil record, they did not become common until ~550-520 Ma when independent acquisitions of biomineralization appeared in multiple lineages of animals and a few protists (single-celled eukaryotes). Evidence of biomineralization preceding the late Ediacaran is spotty aside from the apatitic scale microfossils of the ~811 Ma Fifteenmile Group, northwestern Canada. Here, we describe scale-shaped microfossils from four vase-shaped microfossil (VSM)-bearing units of later Tonian age: the Togari Group of Tasmania, Chuar and Pahrump groups of southwestern United States, and the Roaldtoppen Group of Svalbard. These scale-shaped microfossils consist of thin, ~13 micron-long plates typically surrounded by a 1-3 micron-thick colorless envelope; they are found singly and in heterotypic and monotypic clusters of a few to >20 specimens. Raman spectroscopy and confocal laser scanning microscopy indicate these microfossils are composed of apatite and kerogen, just as is seen in the Fifteenmile Group scale microfossils. Despite compositional similarity, however, these scales are probably not homologous, representing instead, an independent acquisition of apatite mineralization. We propose that these apatite-kerogen scale-shaped microfossils are skeletal elements of a protistan cell. In particular, their consistent co-occurrence with VSMs, and similarities with scales of arcellinid testate amoebae, a group to which the VSMs are thought to belong, suggest the possibility that these microfossils may be test-forming scales of ancient arcellinid testate amoebae. The apparent apatite biomineralization in both these microfossils and the Fifteenmile scales is unexpected given its exceedingly rare use in skeletons of modern protists. This modern absence is attributed to the extravagance of using a limiting nutrient in a structural element, but multiple occurrences of apatite biomineralization in the Tonian suggest that phosphorus was not a limiting nutrient for these organisms, a suggestion consistent with the idea that dissolved seawater phosphate concentrations may have been higher at this time.
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Affiliation(s)
- Leigh Anne Riedman
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
- Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Susannah M Porter
- Department of Earth Science, University of California at Santa Barbara, Santa Barbara, CA, USA
| | - Andrew D Czaja
- Department of Geology, University of Cincinnati, Cincinnati, OH, USA
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10
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Abstract
Phagocytosis, or 'cell eating', is a eukaryote-specific process where particulate matter is engulfed via invaginations of the plasma membrane. The origin of phagocytosis has been central to discussions on eukaryogenesis for decades-, where it is argued as being either a prerequisite for, or consequence of, the acquisition of the ancestral mitochondrion. Recently, genomic and cytological evidence has increasingly supported the view that the pre-mitochondrial host cell-a bona fide archaeon branching within the 'Asgard' archaea-was incapable of phagocytosis and used alternative mechanisms to incorporate the alphaproteobacterial ancestor of mitochondria. Indeed, the diversity and variability of proteins associated with phagosomes across the eukaryotic tree suggest that phagocytosis, as seen in a variety of extant eukaryotes, may have evolved independently several times within the eukaryotic crown-group. Since phagocytosis is critical to the functioning of modern marine food webs (without it, there would be no microbial loop or animal life), multiple late origins of phagocytosis could help explain why many of the ecological and evolutionary innovations of the Neoproterozoic Era (e.g. the advent of eukaryotic biomineralization, the 'Rise of Algae' and the origin of animals) happened when they did.
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Affiliation(s)
- Daniel B. Mills
- Department of Geological Sciences, Stanford University, Stanford, CA 94305, USA
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