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Pérez-Pinedo D, Nicholls R, Neville JM, McIlroy D. Hydrodynamic insights into the paleobiology of the Ediacaran rangeomorph Fractofusus misrai. iScience 2024; 27:110107. [PMID: 38947528 PMCID: PMC11214322 DOI: 10.1016/j.isci.2024.110107] [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: 11/21/2023] [Revised: 03/10/2024] [Accepted: 05/23/2024] [Indexed: 07/02/2024] Open
Abstract
The Ediacaran of Newfoundland preserves some of the oldest complex macroscopic communities, several of which are dominated by the fractal-like rangeomorph genus Fractofusus. Here we use computational fluid dynamics and a detailed reconstruction of Fractofusus misrai to document for the first time hydrodynamic phenomena associated with this sediment-reclining organism and its rangeomorph elements that are relevant to interpreting feeding strategies, explain the recently documented rheotropic growth oblique to currents, and provide insights into their impact on the Ediacaran seafloor. Obliquely oriented Fractofusus are common, likely representing a compromise between maximized aspect ratio and minimization of drag. Flow patterns on the upper surface of Fractofusus are consistent with the collection of dissolved and finely particulate nutrients, as well as gas exchange. Fractofusus produce a wake downstream, demonstrating that reclining rangeomorphs had potential to modify sedimentation patterns on the ancient seafloor by potentially allowing deposition of fine-grained sediment.
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Affiliation(s)
- Daniel Pérez-Pinedo
- Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL A1B3X5, Canada
| | | | - Jenna M. Neville
- Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL A1B3X5, Canada
| | - Duncan McIlroy
- Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL A1B3X5, Canada
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2
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Mussini G, Dunn FS. Decline and fall of the Ediacarans: late-Neoproterozoic extinctions and the rise of the modern biosphere. Biol Rev Camb Philos Soc 2024; 99:110-130. [PMID: 37667585 DOI: 10.1111/brv.13014] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 08/22/2023] [Accepted: 08/25/2023] [Indexed: 09/06/2023]
Abstract
The end-Neoproterozoic transition marked a gradual but permanent shift between distinct configurations of Earth's biosphere. This interval witnessed the demise of the enigmatic Ediacaran Biota, ushering in the structured trophic webs and disparate animal body plans of Phanerozoic ecosystems. However, little consensus exists on the reality, drivers, and macroevolutionary implications of end-Neoproterozoic extinctions. Here we evaluate potential drivers of late-Neoproterozoic turnover by addressing recent findings on Ediacaran geochronology, the persistence of classical Ediacaran macrobionts into the Cambrian, and the existence of Ediacaran crown-group eumetazoans. Despite renewed interest in the possibility of Phanerozoic-style 'mass extinctions' in the latest Neoproterozoic, our synthesis of the available evidence does not support extinction models based on episodic geochemical triggers, nor does it validate simple ecological interpretations centred on direct competitive displacement. Instead, we argue that the protracted and indirect effects of early bilaterian innovations, including escalations in sediment engineering, predation, and the largely understudied impacts of reef-building, may best account for the temporal structure and possible selectivity of late-Neoproterozoic extinctions. We integrate these processes into a generalised model of early eumetazoan-dominated ecologies, charting the disruption of spatial and temporal isotropy on the Ediacaran benthos as a consequence of diversifying macrofaunal interactions. Given the nature of resource distribution in Ediacaran ecologies, the continuities among Ediacaran and Cambrian faunas, and the convergent origins of ecologically disruptive innovations among bilaterians we suggest that the rise of Phanerozoic-type biotas may have been unstoppable.
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Affiliation(s)
- Giovanni Mussini
- Department of Earth Sciences, Downing Street, University of Cambridge, Cambridge, CB2 3EQ, UK
| | - Frances S Dunn
- Oxford University Museum of Natural History, Parks Road, University of Oxford, Oxford, OX1 3PW, UK
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3
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Hou JB, Hughes NC, Hopkins MJ, Shu D. Gill function in an early arthropod and the widespread adoption of the countercurrent exchange mechanism. ROYAL SOCIETY OPEN SCIENCE 2023; 10:230341. [PMID: 37593708 PMCID: PMC10427831 DOI: 10.1098/rsos.230341] [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: 03/19/2023] [Accepted: 07/25/2023] [Indexed: 08/19/2023]
Abstract
Rising but fluctuating oxygen levels in the Early Palaeozoic provide an environmental context for the radiation of early metazoans, but little is known about how mechanistically early animals satisfied their oxygen requirements. Here we propose that the countercurrent gaseous exchange, a highly efficient respiratory mechanism, was effective in the gills of the Late Ordovician trilobite Triarthrus eatoni. In order to test this, we use computational fluid dynamics to simulate water flow around its gills and show that water velocity decreased distinctly in front of and between the swollen ends, which first encountered the oxygen-charged water, and slowed continuously at the mid-central region, forming a buffer zone with a slight increase of the water volume. In T. eatoni respiratory surface area was maximized by extending filament height and gill shaft length. In comparison with the oxygen capacity of modern fish and crustaceans, a relatively low weight specific area in T. eatoni may indicate its low oxygen uptake, possibly related to a less active life mode. Exceptionally preserved respiratory structures in the Cambrian deuterostome Haikouella are also consistent with a model of countercurrent gaseous exchange, exemplifying the wide adoption of this strategy among early animals.
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Affiliation(s)
- Jin-Bo Hou
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210023, People's Republic of China
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
| | - Nigel C. Hughes
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521, USA
| | - Melanie J. Hopkins
- Division of Paleontology (Invertebrates), American Museum of Natural History, New York, NY 10024, USA
| | - Degan Shu
- Early Life Institute and State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, People's Republic of China
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4
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Darroch SA, Gutarra S, Masaki H, Olaru A, Gibson BM, Dunn FS, Mitchell EG, Racicot RA, Burzynski G, Rahman IA. The rangeomorph Pectinifrons abyssalis: Hydrodynamic function at the dawn of animal life. iScience 2023; 26:105989. [PMID: 36756377 PMCID: PMC9900436 DOI: 10.1016/j.isci.2023.105989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 12/06/2022] [Accepted: 01/12/2023] [Indexed: 01/18/2023] Open
Abstract
Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P. abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P. abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals.
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Affiliation(s)
- Simon A.F. Darroch
- Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA,Evolutionary Studies Institute, Vanderbilt University, Nashville, TN 37235, USA,Senckenberg Research Institute and Natural History Museum Frankfurt, 60325 Frankfurt, Germany
| | | | - Hale Masaki
- Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA
| | - Andrei Olaru
- Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA
| | - Brandt M. Gibson
- Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA,Department of Chemistry and Physical Sciences, University of Toronto Mississauga, Mississauga, ON L5L 1C6, Canada
| | - Frances S. Dunn
- Oxford University Museum of Natural History, University of Oxford, Oxford OX1 3PW, UK
| | - Emily G. Mitchell
- Department of Zoology, Museum of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
| | - Rachel A. Racicot
- Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37240, USA,Evolutionary Studies Institute, Vanderbilt University, Nashville, TN 37235, USA,Senckenberg Research Institute and Natural History Museum Frankfurt, 60325 Frankfurt, Germany
| | - Gregory Burzynski
- Department of Biology, Fairfield University, Fairfield, CT 06824, USA
| | - Imran A. Rahman
- The Natural History Museum, London SW7 5BD, UK,Oxford University Museum of Natural History, University of Oxford, Oxford OX1 3PW, UK,Corresponding author
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5
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Aria C. The origin and early evolution of arthropods. Biol Rev Camb Philos Soc 2022; 97:1786-1809. [PMID: 35475316 DOI: 10.1111/brv.12864] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Revised: 04/12/2022] [Accepted: 04/14/2022] [Indexed: 12/18/2022]
Abstract
The rise of arthropods is a decisive event in the history of life. Likely the first animals to have established themselves on land and in the air, arthropods have pervaded nearly all ecosystems and have become pillars of the planet's ecological networks. Forerunners of this saga, exceptionally well-preserved Palaeozoic fossils recently discovered or re-discovered using new approaches and techniques have elucidated the precocious appearance of extant lineages at the onset of the Cambrian explosion, and pointed to the critical role of the plankton and hard integuments in early arthropod diversification. The notion put forward at the beginning of the century that the acquisition of extant arthropod characters was stepwise and represented by the majority of Cambrian fossil taxa is being rewritten. Although some key traits leading to Euarthropoda are indeed well documented along a diversified phylogenetic stem, this stem led to several speciose and ecologically diverse radiations leaving descendants late into the Palaeozoic, and a large part, if not all of the Cambrian euarthropods can now be placed on either of the two extant lineages: Mandibulata and Chelicerata. These new observations and discoveries have altered our view on the nature and timing of the Cambrian explosion and clarified diagnostic characters at the origin of extant arthropods, but also raised new questions, especially with respect to cephalic plasticity. There is now strong evidence that early arthropods shared a homologous frontalmost appendage, coined here the cheira, which likely evolved into antennules and chelicerae, but other aspects, such as brain and labrum evolution, are still subject to active debate. The early evolution of panarthropods was generally driven by increased mastication and predation efficiency and sophistication, but a wealth of recent studies have also highlighted the prevalent role of suspension-feeding, for which early panarthropods developed their own adaptive feedback through both specialized appendages and the diversification of small, morphologically differentiated larvae. In a context of general integumental differentiation and hardening across Cambrian metazoans, arthrodization of body and limbs notably prompted two diverging strategies of basipod differentiation, which arguably became founding criteria in the divergence of total-groups Mandibulata and Chelicerata. The kinship of trilobites and their relatives remains a source of disagreement, but a recent topological solution, termed the 'deep split', could embed Artiopoda as sister taxa to chelicerates and constitute definitive support for Arachnomorpha. Although Cambrian fossils have been critical to all these findings, data of exceptional quality have also been accumulating from other Palaeozoic Konservat-Lagerstätten, and a better integration of this information promises a much more complete and elaborate picture of early arthropod evolution in the near future. From the broader perspective of a total-evidence approach to the understanding of life's history, and despite persisting systematic debates and new interpretative challenges, various advances based on palaeontological evidence open the prospect of finally using the full potential of the most diverse animal phylum to investigate macroevolutionary patterns and processes.
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Affiliation(s)
- Cédric Aria
- 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, P. R. China.,Shaanxi Key Laboratory of Early Life and Environments, Northwest University, Xi'an, 710069, P.R. China
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6
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Bicknell RD, Smith PM, Brougham T, Bevitt JJ. An earliest Triassic age for Tasmaniolimulus and comments on synchrotron tomography of Gondwanan horseshoe crabs. PeerJ 2022; 10:e13326. [PMID: 35480564 PMCID: PMC9037155 DOI: 10.7717/peerj.13326] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 04/02/2022] [Indexed: 01/13/2023] Open
Abstract
Constraining the timing of morphological innovations within xiphosurid evolution is central for understanding when and how such a long-lived group exploited vacant ecological niches over the majority of the Phanerozoic. To expand the knowledge on the evolution of select xiphosurid forms, we reconsider the four Australian taxa: Austrolimulus fletcheri, Dubbolimulus peetae, Tasmaniolimulus patersoni, and Victalimulus mcqueeni. In revisiting these taxa, we determine that, contrary to previous suggestion, T. patersoni arose after the Permian and the origin of over-developed genal spine structures within Austrolimulidae is exclusive to the Triassic. To increase the availability of morphological data pertaining to these unique forms, we also examined the holotypes of the four xiphosurids using synchrotron radiation X-ray tomography (SRXT). Such non-destructive, in situ imaging of palaeontological specimens can aid in the identification of novel morphological data by obviating the need for potentially extensive preparation of fossils from the surrounding rock matrix. This is particularly important for rare and/or delicate holotypes. Here, SRXT was used to emphasize A. fletcheri and T. patersoni cardiac lobe morphologies and illustrate aspects of the V. mcqueeni thoracetronic doublure, appendage impressions, and moveable spine notches. Unfortunately, the strongly compacted D. peetae precluded the identification of any internal structures, but appendage impressions were observed. The application of computational fluid dynamics to high-resolution 3D reconstructions are proposed to understand the hydrodynamic properties of divergent genal spine morphologies of austrolimulid xiphosurids.
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Affiliation(s)
| | - Patrick M. Smith
- Australian Museum Research Institute, Sydney, Australia,Macquarie University, Sydney, Australia
| | | | - Joseph J. Bevitt
- Australian Nuclear Science and Technology Organisation, Sydney, Australia
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7
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Plummer PS. Was the Amadeus Basin of Central Australia a crucible for pre-Ediacaran macro-biotic evolutionary trials? T ROY SOC SOUTH AUST 2021. [DOI: 10.1080/03721426.2021.1935585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Phillip S. Plummer
- Department of Earth Sciences, University of Adelaide, Adelaide, South Australia, Australia
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8
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Cracknell K, García-Bellido DC, Gehling JG, Ankor MJ, Darroch SAF, Rahman IA. Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities. Sci Rep 2021; 11:4121. [PMID: 33602958 PMCID: PMC7893023 DOI: 10.1038/s41598-021-83452-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Accepted: 02/03/2021] [Indexed: 01/31/2023] Open
Abstract
Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and evolution, with implications for understanding the origins of the modern marine biosphere. Here, we use three-dimensional modelling and computational fluid dynamics to establish the feeding mode of the enigmatic Ediacaran pentaradial eukaryote Arkarua. Through comparisons with two Cambrian echinoderms, Cambraster and Stromatocystites, we show that flow patterns around Arkarua strongly support its interpretation as a passive suspension feeder. Arkarua is added to the growing number of Ediacaran benthic suspension feeders, suggesting that the energy link between pelagic and benthic ecosystems was likely expanding in the White Sea assemblage (~ 558-550 Ma). The advent of widespread suspension feeding could therefore have played an important role in the subsequent waves of ecological innovation and escalation that culminated with the Cambrian explosion.
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Affiliation(s)
- Kelsie Cracknell
- grid.5337.20000 0004 1936 7603School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ UK
| | - Diego C. García-Bellido
- grid.1010.00000 0004 1936 7304School of Biological Sciences, University of Adelaide, North Terrace Campus, Adelaide, South Australia 5005 Australia ,grid.437963.c0000 0001 1349 5098South Australian Museum, Adelaide, South Australia 5000 Australia
| | - James G. Gehling
- grid.437963.c0000 0001 1349 5098South Australian Museum, Adelaide, South Australia 5000 Australia
| | - Martin J. Ankor
- grid.1010.00000 0004 1936 7304Department of Earth Sciences and Sprigg Geobiology Centre, University of Adelaide, North Terrace Campus, Adelaide, South Australia 5005 Australia
| | - Simon A. F. Darroch
- grid.152326.10000 0001 2264 7217Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN 37235-1805 USA ,grid.462628.c0000 0001 2184 5457Senckenberg Museum of Natural History, 60325 Frankfurt, Germany
| | - Imran A. Rahman
- grid.440504.10000 0000 8693 4250Oxford University Museum of Natural History, Oxford, OX1 3PW UK
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9
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Gibson BM, Furbish DJ, Rahman IA, Schmeeckle MW, Laflamme M, Darroch SAF. Ancient life and moving fluids. Biol Rev Camb Philos Soc 2020; 96:129-152. [PMID: 32959981 PMCID: PMC7821342 DOI: 10.1111/brv.12649] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Revised: 08/21/2020] [Accepted: 08/25/2020] [Indexed: 11/27/2022]
Abstract
Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft‐bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in‐depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.
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Affiliation(s)
- Brandt M Gibson
- Department of Earth and Environmental Sciences, Vanderbilt University, PMB 351805, 2301 Vanderbilt Place, Nashville, TN, 37235-1805, U.S.A
| | - David J Furbish
- Department of Earth and Environmental Sciences, Vanderbilt University, PMB 351805, 2301 Vanderbilt Place, Nashville, TN, 37235-1805, U.S.A
| | - Imran A Rahman
- Oxford University Museum of Natural History, Parks Road, Oxford, OX1 3PW, U.K
| | - Mark W Schmeeckle
- School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ, 85281, U.S.A
| | - Marc Laflamme
- Department of Chemical and Physical Sciences, University of Toronto Mississauga, 3356 Mississauga Rd North, Mississauga, Ontario, L5L 1C6, Canada
| | - Simon A F Darroch
- Department of Earth and Environmental Sciences, Vanderbilt University, PMB 351805, 2301 Vanderbilt Place, Nashville, TN, 37235-1805, U.S.A
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10
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Santagata S. Genes with evidence of positive selection as potentially related to coloniality and the evolution of morphological features among the lophophorates and entoprocts. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2020; 336:267-280. [PMID: 32638536 DOI: 10.1002/jez.b.22975] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 05/14/2020] [Accepted: 06/03/2020] [Indexed: 02/06/2023]
Abstract
Evolutionary mechanisms that underlie the origins of coloniality among organisms are diverse. Some animal colonies may be comprised strictly of clonal individuals formed from asexual budding or comprised of a chimera of clonal and sexually produced individuals that fuse secondarily. This investigation focuses on select members of the lophophorates and entoprocts whose evolutionary relationships remain enigmatic even in the age of genomics. Using transcriptomic data sets, two coloniality-based hypotheses are tested in a phylogenetic context to find candidate genes showing evidence of positive selection and potentially convergent molecular signatures among solitary species and taxa-forming colonies from aggregate groups or clonal budding. Approximately 22% of the 387 orthogroups tested showed evidence of positive selection in at least one of the three branch-site tests (CODEML, BUSTED, and aBSREL). Only 12 genes could be reliably associated with a developmental function related to traits linked with coloniality, neuroanatomy, or ciliary fields. Genes testing for both positive selection and convergent molecular characters include orthologues of Radial spoke head, Elongation translation initiation factors, SEC13, and Immediate early response gene5. Maximum likelihood analyses included here resulted in tree topologies typical of other phylogenetic investigations based on wider genomic information. Further genomic and experimental evidence will be needed to resolve whether a solitary ancestor with multiciliated cells that formed aggregate groups gave rise to colonial forms in bryozoans (and perhaps the entoprocts) or that the morphological differences exhibited by phoronids and brachiopods represent trait modifications from a colonial ancestor.
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Affiliation(s)
- Scott Santagata
- Department of Biological and Environmental Sciences, Long Island University, Greenvale, New York
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11
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Schiffbauer JD, Selly T, Jacquet SM, Merz RA, Nelson LL, Strange MA, Cai Y, Smith EF. Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period. Nat Commun 2020; 11:205. [PMID: 31924764 PMCID: PMC6954273 DOI: 10.1038/s41467-019-13882-z] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Accepted: 12/04/2019] [Indexed: 11/08/2022] Open
Abstract
The fossil record of the terminal Ediacaran Period is typified by the iconic index fossil Cloudina and its relatives. These tube-dwellers are presumed to be primitive metazoans, but resolving their phylogenetic identity has remained a point of contention. The root of the problem is a lack of diagnostic features; that is, phylogenetic interpretations have largely centered on the only available source of information-their external tubes. Here, using tomographic analyses of fossils from the Wood Canyon Formation (Nevada, USA), we report evidence of recognizable soft tissues within their external tubes. Although alternative interpretations are plausible, these internal cylindrical structures may be most appropriately interpreted as digestive tracts, which would be, to date, the earliest-known occurrence of such features in the fossil record. If this interpretation is correct, their nature as one-way through-guts not only provides evidence for establishing these fossils as definitive bilaterians but also has implications for the long-debated phylogenetic position of the broader cloudinomorphs.
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Affiliation(s)
- James D Schiffbauer
- Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA.
- X-ray Microanalysis Core, University of Missouri, Columbia, MO, 65211, USA.
| | - Tara Selly
- Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA.
- X-ray Microanalysis Core, University of Missouri, Columbia, MO, 65211, USA.
| | - Sarah M Jacquet
- Department of Geological Sciences, University of Missouri, Columbia, MO, 65211, USA
| | - Rachel A Merz
- Biology Department, Swarthmore College, Swarthmore, PA, 19081, USA
| | - Lyle L Nelson
- Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Michael A Strange
- Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV, 89154, USA
| | - Yaoping Cai
- Shaanxi Key Laboratory of Early Life and Environment, State Key Laboratory of Continental Dynamics, and Department of Geology, Northwest University, Xi'an, 710069, China
| | - Emily F Smith
- Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, 21218, USA
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12
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Cribb AT, Kenchington CG, Koester B, Gibson BM, Boag TH, Racicot RA, Mocke H, Laflamme M, Darroch SAF. Increase in metazoan ecosystem engineering prior to the Ediacaran-Cambrian boundary in the Nama Group, Namibia. ROYAL SOCIETY OPEN SCIENCE 2019; 6:190548. [PMID: 31598294 PMCID: PMC6774933 DOI: 10.1098/rsos.190548] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 08/23/2019] [Indexed: 05/20/2023]
Abstract
The disappearance of the soft-bodied Ediacara biota at the Ediacaran-Cambrian boundary potentially represents the earliest mass extinction of complex life, although the precise driver(s) of this extinction remain unresolved. The 'biotic replacement' model proposes that an evolutionary radiation of metazoan ecosystem engineers in the latest Ediacaran profoundly altered marine palaeoenvironments, resulting in the extinction of Ediacara biota and setting the stage for the subsequent Cambrian Explosion. However, metazoan ecosystem engineering across the Ediacaran-Cambrian transition has yet to be quantified. Here, we test this key tenet of the biotic replacement model by characterizing the intensity of metazoan bioturbation and ecosystem engineering in trace fossil assemblages throughout the latest Ediacaran Nama Group in southern Namibia. The results illustrate a dramatic increase in both bioturbation and ecosystem engineering intensity in the latest Ediacaran, prior to the Cambrian boundary. Moreover, our analyses demonstrate that the highest-impact ecosystem engineering behaviours were present well before the onset of the Cambrian. These data provide the first support for a fundamental prediction of the biotic replacement model, and evidence for a direct link between the early evolution of ecosystem engineering and the extinction of the Ediacara biota.
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Affiliation(s)
- Alison T. Cribb
- Earth and Environmental Science, Vanderbilt University, Nashville, TN 37235-1805, USA
- Earth Sciences, University of Southern California, Los Angeles, CA 90089-0740, USA
| | | | - Bryce Koester
- Earth and Environmental Science, Vanderbilt University, Nashville, TN 37235-1805, USA
- Department of Biodiversity, Drexel University, Philadelphia, PA, 19104, USA
| | - Brandt M. Gibson
- Earth and Environmental Science, Vanderbilt University, Nashville, TN 37235-1805, USA
| | - Thomas H. Boag
- Geological Sciences, Stanford University, Stanford, CA 94304, USA
| | - Rachel A. Racicot
- Earth and Environmental Science, Vanderbilt University, Nashville, TN 37235-1805, USA
| | - Helke Mocke
- Geological Survey of Namibia, Ministry of Mines and Energy, Windhoek, Namibia
| | - Marc Laflamme
- Chemical and Physical Sciences, University of Toronto Mississauga, Mississauga, Ontario, CanadaL5L 1C6
| | - Simon A. F. Darroch
- Earth and Environmental Science, Vanderbilt University, Nashville, TN 37235-1805, USA
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