A review of the Ordovician acritarch genus<i>Barakella</i>Cramer &amp; Díez 1977

Yan, Kui; Li, Jun; Molyneux, Stewart G.; Raevskaya, Elena; Servais, Thomas

doi:10.1080/01916122.2017.1366747

Cited by 12 publications

(7 citation statements)

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“…1.5–6). Regardless of their potential origin(s), these striking connections between disparate collections of form taxa tend to suggest that a high level of taxonomic confusion (and potentially inflation) exists beyond that evidenced within the genus Skiagia and would warrant a critical evaluation of taxonomic boundaries and co-occurrence patterns using morphometric means (e.g., Stricanne and Servais 2002; Wang et al 2017; Yan et al 2017; Kroeck et al 2020).…”

Section: Discussionmentioning

confidence: 99%

“…This ordination technique has been widely used in paleontology to help discriminate species based on morphological criteria in groups as varied as sharks (Marramà and Kriwet 2017), killifish (Reichenbacher et al 2007), plants (Álvarez et al 2009), bees (De Meulemeester et al 2012), bryozoans (Cheetham 1986), mollusks (Geary 1992; Marko and Jackson 2001; Reyment 2003), trilobites (Labandeira and Hughes 1994), and brachiopods (Kowalewski et al 1997; Carranza and Carlson 2021). LDA has also been used as a quantitative tool for taxonomic revision of various upper Cambrian and Ordovician acritarch taxa (Wang et al 2017; Yan et al 2017; Kroeck et al 2020).…”

Section: Methodsmentioning

confidence: 99%

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Morphometric analysis ofSkiagia-plexus acritarchs from the early Cambrian of North Greenland: toward a meaningful evaluation of phenotypic plasticity

2022

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The Cambrian evolutionary radiations are marked by spectacular biotic turnovers and the establishment of increasingly tiered food chains. At the base of these food chains are primary producers, which in the Cambrian fossil record are chiefly represented among organic-walled microfossils. The majority of these microfossil remains have traditionally been attributed to an informal category of incertae sedis called “acritarchs,” based entirely on form taxonomy. Acritarch form taxa have been intensely used for biostratigraphy and in large-scale studies of phytoplankton diversity. However, both prospects have been challenged by cases of taxonomic inconsistencies and oversplitting arising from the large phenotypic plasticity seen among these microfossils. The acritarch form genus Skiagia stands as an ideal case study to explore these taxonomic challenges, because it encompasses a number of form species widely used in lower Cambrian biostratigraphy. Moreover, subtle morphological differences among Skiagia species were suggested to underlie key evolutionary innovations toward complex reproductive strategies. Here we apply a multivariate morphometric approach to investigate the morphological variation of Skiagia-plexus acritarchs using an assemblage sourced from the Buen Formation (Cambrian Series 2, Stages 3–4) of North Greenland. Our analysis showed that the species-level classification of Skiagia discretizes a continuous spectrum of morphologies. While these findings bring important taxonomic and biostratigraphic hurdles to light, the unequal frequency distribution of life cycle stages among Skiagia species suggests that certain elements of phytoplankton paleobiology are nonetheless captured by Skiagia form taxonomy. These results demonstrate the value of using morphometric tools to explore acritarch phenotypic plasticity and its potential ontogenetic and paleoecological drivers in Cambrian ecosystems.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Morphometric analysis ofSkiagia-plexus acritarchs from the early Cambrian of North Greenland: toward a meaningful evaluation of phenotypic plasticity

2022

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“…In South China, the FAD of the genus is placed in Stage Slice Fl1 in the lower or middle Floian, in the lower part of Time‐Slice 2b or possibly in 2a (Yan et al . ). On Avalonia, Molyneux () recorded the genus from the upper part of the Moridunian Stage of the Arenig Series in South Wales, approximately equivalent to Time‐Slice 2b (Fig.…”

Section: Fads Of Selected Acritarch Morphotypesmentioning

confidence: 97%

First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician

Servais

Molyneux

et al. 2018

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First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity.

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“…Several acritarch taxa have been proposed as indicators for the peri-Gondwanan province: Arbusculidium, Coryphidium and Striatotheca are restricted to the peri-Gondwana margin (Li 1989). Barakella and Vavrdovella are also considered to be characteristic for this palaeoprovince (Tongiorgi and Di Milia 1999;Li and Servais 2002;Yan et al 2017). With all occurrences of Virgatasporites and Attritasporites coming from the margins of Gondwana, it may be worth considering to include these taxa also as indicators for the peri-Gondwanan acritarch province.…”

Section: Palaeobiogeographical Distribution Of Attritasporites and Vi...mentioning

confidence: 99%

Virgatasporites and Attritasporites: the oldest land plant derived spores, cryptospores or acritarchs?

et al. 2022

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The oldest reported occurrence of cryptospores supposed to derive from land plants (embryophytes) is currently considered to be in the Middle Ordovician. The two genera Virgatasporites and Attritasporites, described in the 1960ʹs from the Early Ordovician (Tremadocian) of Algeria, are morphologically close to the miospores, and therefore pose a dilemma, because these spore-like microfossils are recorded before the first appearance of the oldest land plant derived spores. Here the taxonomy, biostratigraphy and palaeobiogeography of the two genera and their species are revised. Both genera are found in many localities on the Gondwanan border between the late Cambrian and the Middle Ordovician. They have not been found at the margins of other palaeocontinents so far. The biological affinity of the taxa remains uncertain. Several authors considered the two genera to be spore-like microfossils, whereas other authors classified them as acritarchs, i.e. organic-walled microfossils of unknown biological affinity. As the relationship to the embryophyte lineage cannot be established clearly to date, the biological affiliation remains enigmatic. Therefore, in the absence of other evidence, the taxa Virgatasporites and Attritasporites should be temporarily classified as incertae sedis, i.e. as acritarchs, before their true biological affinity is known and they can be adequately placed into a biological group.

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A review of the Ordovician acritarch genusBarakellaCramer & Díez 1977

Cited by 12 publications

References 46 publications

Morphometric analysis ofSkiagia-plexus acritarchs from the early Cambrian of North Greenland: toward a meaningful evaluation of phenotypic plasticity

Morphometric analysis ofSkiagia-plexus acritarchs from the early Cambrian of North Greenland: toward a meaningful evaluation of phenotypic plasticity

First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician

Virgatasporites and Attritasporites: the oldest land plant derived spores, cryptospores or acritarchs?

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