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  • 1
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    Online Resource
    Inference of facultative mobility in the enigmatic Ediacaran organism Parvancorina
    The Royal Society ; 2017
    In:  Biology Letters Vol. 13, No. 5 ( 2017-05), p. 20170033-
    Details
    In: Biology Letters, The Royal Society, Vol. 13, No. 5 ( 2017-05), p. 20170033-
    Abstract: Establishing how Ediacaran organisms moved and fed is critical to deciphering their ecological and evolutionary significance, but has long been confounded by their non-analogue body plans. Here, we use computational fluid dynamics to quantitatively analyse water flow around the Ediacaran taxon Parvancorina , thereby testing between competing models for feeding mode and mobility. The results show that flow was not distributed evenly across the organism, but was directed towards localized areas; this allows us to reject osmotrophy, and instead supports either suspension feeding or detritivory. Moreover, the patterns of recirculating flow differ substantially with orientation to the current, suggesting that if Parvancorina was a suspension feeder, it would have been most efficient if it was able to re-orient itself with respect to current direction, and thus ensure flow was directed towards feeding structures. Our simulations also demonstrate that the amount of drag varied with orientation, indicating that Parvancorina would have greatly benefited from adjusting its position to minimize drag. Inference of facultative mobility in Parvancorina suggests that Ediacaran benthic ecosystems might have possessed a higher proportion of mobile taxa than currently appreciated from trace fossil studies. Furthermore, this inference of movement suggests the presence of musculature or appendages that are not preserved in fossils, but which would noneltheless support a bilaterian affinity for Parvancorina .
    Type of Medium: Online Resource
    ISSN: 1744-9561 , 1744-957X
    URL: Article
    DOI: 10.1098/rsbl.2017.0033
    Language: English
    Publisher: The Royal Society
    Publication Date: 2017
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  • 2
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    Biotic replacement and mass extinction of the Ediacara biota
    The Royal Society ; 2015
    In:  Proceedings of the Royal Society B: Biological Sciences Vol. 282, No. 1814 ( 2015-09-07), p. 20151003-
    Details
    In: Proceedings of the Royal Society B: Biological Sciences, The Royal Society, Vol. 282, No. 1814 ( 2015-09-07), p. 20151003-
    Abstract: The latest Neoproterozoic extinction of the Ediacara biota has been variously attributed to catastrophic removal by perturbations to global geochemical cycles, ‘biotic replacement’ by Cambrian-type ecosystem engineers, and a taphonomic artefact. We perform the first critical test of the ‘biotic replacement’ hypothesis using combined palaeoecological and geochemical data collected from the youngest Ediacaran strata in southern Namibia. We find that, even after accounting for a variety of potential sampling and taphonomic biases, the Ediacaran assemblage preserved at Farm Swartpunt has significantly lower genus richness than older assemblages. Geochemical and sedimentological analyses confirm an oxygenated and non-restricted palaeoenvironment for fossil-bearing sediments, thus suggesting that oxygen stress and/or hypersalinity are unlikely to be responsible for the low diversity of communities preserved at Swartpunt. These combined analyses suggest depauperate communities characterized the latest Ediacaran and provide the first quantitative support for the biotic replacement model for the end of the Ediacara biota. Although more sites (especially those recording different palaeoenvironments) are undoubtedly needed, this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.
    Type of Medium: Online Resource
    ISSN: 0962-8452 , 1471-2954
    URL: Article
    DOI: 10.1098/rspb.2015.1003
    Language: English
    Publisher: The Royal Society
    Publication Date: 2015
    detail.hit.zdb_id: 1460975-7
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    SSG: 25
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  • 3
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    Gregarious suspension feeding in a modular Ediacaran organism
    American Association for the Advancement of Science (AAAS) ; 2019
    In:  Science Advances Vol. 5, No. 6 ( 2019-06-07)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 5, No. 6 ( 2019-06-07)
    Abstract: Reconstructing Precambrian eukaryotic paleoecology is pivotal to understanding the origins of the modern, animal-dominated biosphere. Here, we combine new fossil data from southern Namibia with computational fluid dynamics (CFD) to test between competing feeding models for the Ediacaran taxon Ernietta . In addition, we perform simulations for multiple individuals, allowing us to analyze hydrodynamics of living communities. We show that Ernietta lived gregariously, forming shallow marine aggregations in the latest Ediacaran, 548 to 541 million years (Ma) ago. We demonstrate enhanced vertical mixing of the water column above aggregations and preferential redirection of current into body cavities of downstream individuals. These results support the reconstruction of Ernietta as a macroscopic suspension feeder and also provide a convincing paleoecological advantage to feeding in aggregations analogous to those recognized in many extant marine metazoans. These results provide some of the oldest evidence of commensal facilitation by macroscopic eukaryotes yet recognized in the fossil record.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.aaw0260
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2019
    detail.hit.zdb_id: 2810933-8
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  • 4
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    Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems
    American Association for the Advancement of Science (AAAS) ; 2015
    In:  Science Advances Vol. 1, No. 10 ( 2015-11-06)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 1, No. 10 ( 2015-11-06)
    Abstract: The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical “pits.” These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.1500800
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2015
    detail.hit.zdb_id: 2810933-8
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  • 5
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    The life and times of Pteridinium simplex
    Cambridge University Press (CUP) ; 2022
    In:  Paleobiology Vol. 48, No. 4 ( 2022-11), p. 527-556
    Details
    In: Paleobiology, Cambridge University Press (CUP), Vol. 48, No. 4 ( 2022-11), p. 527-556
    Abstract: Pteridinium simplex is an iconic erniettomorph taxon best known from late Ediacaran successions in South Australia, Russia, and Namibia. Despite nearly 100 years of study, there remain fundamental questions surrounding the paleobiology and paleoecology of this organism, including its life position relative to the sediment–water interface, and how it fed and functioned within benthic communities. Here, we combine a redescription of specimens housed at the Senckenberg Forschungsinstitut und Naturmuseum Frankfurt with field observations of fossiliferous surfaces, to constrain the life habit of Pteridinium and gain insights into the character of benthic ecosystems shortly before the beginning of the Cambrian. We present paleontological and sedimentological evidence suggesting that Pteridinium was semi-infaunal and lived gregariously in aggregated communities, preferentially adopting an orientation with the long axis perpendicular to the prevailing current direction. Using computational fluid dynamics simulations, we demonstrate that this life habit could plausibly have led to suspended food particles settling within the organism's central cavity. This supports interpretation of Pteridinium as a macroscopic suspension feeder that functioned similarly to the coeval erniettomorph Ernietta , emblematic of a broader paleoecological shift toward benthic suspension-feeding strategies over the course of the latest Ediacaran. Finally, we discuss how this new reconstruction of Pteridinium provides information concerning its potential relationships with extant animal groups and state a case for reconstructing Pteridinium as a colonial metazoan.
    Type of Medium: Online Resource
    ISSN: 0094-8373 , 1938-5331
    URL: Article
    DOI: 10.1017/pab.2022.2
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2022
    detail.hit.zdb_id: 2052186-8
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  • 6
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    The role of iron in the formation of Ediacaran ‘death masks’
    Wiley ; 2023
    In:  Geobiology Vol. 21, No. 4 ( 2023-07), p. 421-434
    Details
    In: Geobiology, Wiley, Vol. 21, No. 4 ( 2023-07), p. 421-434
    Abstract: The Ediacara biota are an enigmatic group of Neoproterozoic soft‐bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic “death masks” mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing “death masks” produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a “perfect storm” of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions.
    Type of Medium: Online Resource
    ISSN: 1472-4677 , 1472-4669
    URL: Issue
    URL: Article
    DOI: 10.1111/gbi.v21.4
    DOI: 10.1111/gbi.12551
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 2113509-5
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  • 7
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    Integrating morphology and in vivo skeletal mobility with digital models to infer function in brittle star arms
    Wiley ; 2018
    In:  Journal of Anatomy Vol. 233, No. 6 ( 2018-12), p. 696-714
    Details
    In: Journal of Anatomy, Wiley, Vol. 233, No. 6 ( 2018-12), p. 696-714
    Abstract: Brittle stars (Phylum Echinodermata, Class Ophiuroidea) have evolved rapid locomotion employing muscle and skeletal elements within their (usually) five arms to apply forces in a manner analogous to that of vertebrates. Inferring the inner workings of the arm has been difficult as the skeleton is internal and many of the ossicles are sub‐millimeter in size. Advances in 3D visualization and technology have made the study of movement in ophiuroids possible. We developed six virtual 3D skeletal models to demonstrate the potential range of motion of the main arm ossicles, known as vertebrae, and six virtual 3D skeletal models of non‐vertebral ossicles. These models revealed the joint center and relative position of the arm ossicles during near‐maximal range of motion. The models also provide a platform for the comparative evaluation of functional capabilities between disparate ophiuroid arm morphologies. We made observations on specimens of Ophioderma brevispina and Ophiothrix angulata . As these two taxa exemplify two major morphological categories of ophiuroid vertebrae, they provide a basis for an initial assessment of the functional consequences of these disparate vertebral morphologies. These models suggest potential differences in the structure of the intervertebral articulations in these two species, implying disparities in arm flexion mechanics. We also evaluated the differences in the range of motion between segments in the proximal and distal halves of the arm length in a specimen of O. brevispina , and found that the morphology of vertebrae in the distal portion of the arm allows for higher mobility than in the proximal portion. Our models of non‐vertebral ossicles show that they rotate further in the direction of movement than the vertebrae themselves in order to accommodate arm flexion. These findings raise doubts over previous hypotheses regarding the functional consequences of ophiuroid arm disparity. Our study demonstrates the value of integrating experimental data and visualization of articulated structures when making functional interpretations instead of relying on observations of vertebral or segmental morphology alone. This methodological framework can be applied to other ophiuroid taxa to enable comparative functional analyses. It will also facilitate biomechanical analyses of other invertebrate groups to illuminate how appendage or locomotor function evolved.
    Type of Medium: Online Resource
    ISSN: 0021-8782 , 1469-7580
    URL: Issue
    URL: Article
    DOI: 10.1111/joa.2018.233.issue-6
    DOI: 10.1111/joa.12887
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 1474856-3
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  • 8
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    Neuroanatomy and inner ear labyrinths of the narwhal, Monodon monoceros , and beluga, Delphinapterus leucas (Cetacea: Monodontidae)
    Wiley ; 2018
    In:  Journal of Anatomy Vol. 233, No. 4 ( 2018-10), p. 421-439
    Details
    In: Journal of Anatomy, Wiley, Vol. 233, No. 4 ( 2018-10), p. 421-439
    Abstract: Narwhals ( Monodon monoceros ) and belugas ( Delphinapterus leucas ) are the only extant members of the Monodontidae, and are charismatic Arctic‐endemic cetaceans that are at risk from global change. Investigating the anatomy and sensory apparatuses of these animals is essential to understanding their ecology and evolution, and informs efforts for their conservation. Here, we use X‐ray CT scans to compare aspects of the endocranial and inner ear labyrinth anatomy of extant monodontids and use the overall morphology to draw larger inferences about the relationship between morphology and ecology. We show that differences in the shape of the brain, vasculature, and neural canals of both species may relate to differences in diving and other behaviors. The cochleae are similar in morphology in the two species, signifying similar hearing ranges and a close evolutionary relationship. Lastly, we compare two different methods for calculating 90var – a calculation independent of body size that is increasingly being used as a proxy for habitat preference. We show that a ‘direct’ angular measurement method shows significant differences between Arctic and other habitat preferences, but angle measurements based on planes through the semicircular canals do not, emphasizing the need for more detailed study and standardization of this measurement. This work represents the first comparative internal anatomical study of the endocranium and inner ear labyrinths of this small clade of toothed whales.
    Type of Medium: Online Resource
    ISSN: 0021-8782 , 1469-7580
    URL: Issue
    URL: Article
    DOI: 10.1111/joa.2018.233.issue-4
    DOI: 10.1111/joa.12862
    Language: English
    Publisher: Wiley
    Publication Date: 2018
    detail.hit.zdb_id: 1474856-3
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  • 9
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    Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities
    Springer Science and Business Media LLC ; 2021
    In:  Scientific Reports Vol. 11, No. 1 ( 2021-02-18)
    Details
    In: Scientific Reports, Springer Science and Business Media LLC, Vol. 11, No. 1 ( 2021-02-18)
    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.
    Type of Medium: Online Resource
    ISSN: 2045-2322
    URL: Article
    DOI: 10.1038/s41598-021-83452-1
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2021
    detail.hit.zdb_id: 2615211-3
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  • 10
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    Evidence for convergent evolution of ultrasonic hearing in toothed whales (Cetacea: Odontoceti)
    The Royal Society ; 2019
    In:  Biology Letters Vol. 15, No. 5 ( 2019-05-31), p. 20190083-
    Details
    In: Biology Letters, The Royal Society, Vol. 15, No. 5 ( 2019-05-31), p. 20190083-
    Abstract: Toothed whales (Cetacea: Odontoceti) are the most diverse group of modern cetaceans, originating during the Eocene/Oligocene transition approximately 38 Ma. All extant odontocetes echolocate; a single origin for this behaviour is supported by a unique facial source for ultrasonic vocalizations and a cochlea adapted for hearing the corresponding echoes. The craniofacial and inner ear morphology of Oligocene odontocetes support a rapid (less than 5 Myr) early evolution of echolocation. Although some cranial features in the stem odontocetes Simocetus and Olympicetus suggest an ability to generate ultrasonic sound, until now, the bony labyrinths of taxa of this grade have not been investigated. Here, we use µCT to examine a petrosal of a taxon with clear similarities to Olympicetus avitus . Measurements of the bony labyrinth, when added to an extensive dataset of cetartiodactyls, resulted in this specimen sharing a morphospace with stem whales, suggesting a transitional inner ear. This discovery implies that either the lineage leading to this Olympicetus ­-like taxon lost the ability to hear ultrasonic sound, or adaptations for ultrasonic hearing evolved twice, once in xenorophids and again on the stem of the odontocete crown group. We favour the latter interpretation as it matches a well-documented convergence of craniofacial morphology between xenorophids and extant odontocetes.
    Type of Medium: Online Resource
    ISSN: 1744-9561 , 1744-957X
    URL: Article
    DOI: 10.1098/rsbl.2019.0083
    Language: English
    Publisher: The Royal Society
    Publication Date: 2019
    detail.hit.zdb_id: 2103283-X
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