Acritarch
Acritarchs Temporal range:
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A supposed Ediacaran embryo contained within an acritarch from the Doushantuo Formation | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | incertae sedis |
(unranked): | †Acritarcha Evitt, 1963 |
Synonyms | |
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Acritarchs are organic microfossils, known from approximately 1800 million years ago to the present. The classification is a catch all term used to refer to any organic microfossils that cannot be assigned to other groups. Their diversity reflects major ecological events such as the appearance of predation and the Cambrian explosion.
Definition
Acritarchs were originally defined as non-
Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small
While the
Classification
Acritarchs were most likely
The recent application of atomic force microscopy, confocal microscopy, Raman spectroscopy, and other sophisticated analytic techniques to the study of the ultrastructure, life history, and systematic affinities of mineralized, but originally organic-walled microfossils,[7][8][9][10][11] has shown that some acritarchs are actually fossilized microalgae. In the end, it may well be, as Moczydłowska et al. suggested in 2011, that many acritarchs will, in fact, turn out to be algae.[12][13]
Occurrence
Acritarchs are found in sedimentary rocks from the present back into the
The Archean and earliest Proterozoic microfossils termed "acritarchs" may actually be prokaryotes. The earliest eukaryotic acritarchs known (as of 2020) are from between 1950 and 2150 million years ago.[15]
Diversity
At about 1 billion years ago the organisms responsible for acritarchs started to increase in abundance, diversity, size, complexity of shape, and especially, the size and number of spines. Their populations crashed during periods of extensive worldwide glaciations that covered the majority of the planet, but they proliferated in the Cambrian explosion and reached their highest diversity in the Paleozoic. The increased spininess 1000 million years ago possibly resulted from the need for defense against predators, especially predators large enough to swallow them or tear them apart. Other groups of small organisms from the Neoproterozoic era also show signs of anti-predator defenses.[16]
Further evidence that acritarchs were subject to herbivory around this time comes from a consideration of taxon longevity. The abundance of planktonic organisms that evolved between 1,700 and 1,400 million years ago was limited by nutrient availability – a situation which limits the origination of new species because the existing organisms are so specialised to their niches, and no other niches are available for occupation. Approximately 1,000 million years ago, species longevity fell sharply, suggesting that predation pressure, probably by protist herbivores, became an important factor. Predation would have kept populations in check, meaning that some nutrients were left unused, and new niches were available for new species to occupy.[17]
Etymology
Acritarch was coined in 1963 from the
Genera
This is a list of genera according to Fossilid.info.[19]
- Acanthodiacrodium (Ordovician)
- Acrosphaeridium (Ordovician)
- Actipillion (Ordovician)
- Akomachra (Ordovician)
- Ammonidium (Silurian)
- Aranidium (Cambrian)
- Arbusculidium (Cambrian-Ordovician)
- Archaeodiscina (Cambrian)
- Arcosphaeridium (Ordovician)
- Aremoricanium (Ordovician)
- Arkonia (Ordovician)
- Asteridium (Cambrian)
- Athabascaella (Tremadocian, Early Ordovician)
- Axisphaeridium (Ordovician)
- Bacisphaeridium (Ordovician)
- Baltisphaeridium (Cambrian-Silurian)
- Buedingiisphaeridium (Ordovician)
- Caldariola (Cambrian)
- Calyxiella
- Celtiberium
- Cephalonyx
- Ceratophyton (Cambrian)
- Cheleutochroa (Ordovician)
- Chlamydosphaeridia (Ordovician)
- Comasphaeridium (Ordovician)
- Coronitesta (Ordovician)
- Coryphidium (Ordovician)
- Costatilobus (Ordovician)
- Cristallinium (Cambrian)
- Cycloposphaeridium (Ordovician)
- Cymatiogalea (Cambrian)
- Cymatiosphaera (Cambrian-Ordovician)
- Dactylofusa (Ordovician)
- Dasydiacrodium (Cambrian)
- Dicommopalla (Ordovician)
- Dictyosphaera (Paleozoic)
- Dictyosphaeridium (Ordovician)
- Diexallophasis (Silurian)
- Dilatisphaera (Ordovician)
- Domasia (Ordovician-Silurian)
- Dongyesphaera (Paleozoic)
- Elektroriskos (Cambrian)
- Elenia
- Eliasum
- Estiastra (Ordovician)
- Excultibrachium (Ordovician)
- Fimbriaglomerella
- Florisphaeridium (Ordovician)
- Globosphaeridium (Cambrian)
- Goniosphaeridium (Cambrian-Ordovician)
- Gorgonisphaeridium (Ordovician)
- Granomarginata (Cambrian)
- Gyalorhethium (Ordovician)
- Hapsidopalla (Ordovician)
- Helosphaeridium (Ordovician)
- Impluviculus (Cambrian)
- Introvertocystis (Late Cretaceous)
- Izhoria
- Joehvisphaera (Ordovician)
- Korilophyton (Cambrian)
- Kundasphaera (Ordovician)
- Labyrinthosphaeridium (Ordovician)
- Lacunosphaeridium (Ordovician)
- Ladogella
- Leiofusa (Cambrian-Silurian)
- Leiosphaeridia (Cambrian-Silurian)
- Leiovalia (Ordovician)
- Liepaina (Cambrian)
- Liliosphaeridium (Ordovician)
- Lophosphaeridium (Ordovician-Silurian)
- Lunulidia
- Micrhystridium (Ordovician-Silurian)
- Multiplicisphaeridium (Cambiran-Silurian)
- Nanocyclopia (Ordovician)
- Nodosus
- Oppilatala (Silurian)
- Ordovicidium (Ordovician)
- Orthosphaeridium (Ordovician)
- Ovulum (Cambrian)
- Palaeocladophora (Cambrian)
- Palaeomonostroma (Cambrian)
- Peteinosphaeridium (Ordovician)
- Pheoclosterium (Ordovician)
- Pirea (Cambrian)
- Poikilofusa
- Polyancistrodorus (Ordovician)
- Polyedryxium (Ordovician)
- Polygonium (Cambrian-Ordovician)
- Portalites (Permian)
- Priscogaleata (Ordovician)
- Priscotheca
- Protosphaeridium (Silurian)
- Pterospermella
- Pterospermopsis (Ordovician)
- Pulvinosphaeridium (Ordovician)
- Quadrisporites (Permian)
- Raplasphaera (Ordovician)
- Revinotesta (Ordovician)
- Rhopaliophora (Ordovician)
- Saharidia (Ordovician)
- Salopidium (Silurian)
- Satka (Paleozoic)
- Skiagia (Cambrian)
- Solisphaeridium (Ordovician)
- Stellechinatum (Ordovician)
- Stelliferidium (Cambrian)
- Taeniosphaeridium (Ordovician)
- Tasmanites (Ordovician-Silurian)
- Tetraporina (Permian)
- Timofeevia (Cambrian-Ordovician)
- Tranvikium (Ordovician)
- Trichosphaeridium
- Tunisphaeridium (Ordovician-Silurian)
- Tylotopalla (Ordovician)
- Vernanimalcula (Pre-Cambrian)
- Veryhachium (Cambrian-Silurian)
- Villosacapsula (Ordovician)
- Visbysphaera (Silurian)
- Volkovia
- Vulcanisphaera (Cambrian-Ordovician)
- Winwaloeusia (Ordovician)
See also
References
- .
- PMID 16591055– via PNAS.
- S2CID 221527533.
- .
- ISSN 0034-6667.
- PMID 20164911.
- PMID 12089337.
- .
- .
- .
- S2CID 130041483.
- .
- doi:10.3390/geosciences6040057. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
- S2CID 127238427.
- .
- ^ Bengtson, S. (2002). "Origins and early evolution of predation" (PDF). In Kowalewski, M.; Kelley, P.H. (eds.). The fossil record of predation. The Paleontological Society Papers. Vol. 8. The Paleontological Society. pp. 289–317. Retrieved 29 December 2014.
- S2CID 83713101.
- ^ definition of acritarch at dictionary.com
- ^ "Actipillion".
External links
- CIMP Subcommission on Acritarchs* "CIMP Home page". Archived from the original on 17 February 2007. Commission Internationale de Microflore du Paléozoique (CIMP), international commission for Palaeozoic palynology.
- "The Micropalaeontological Society". Archived from the original on 8 December 2004. Retrieved 12 November 2004.
- "The Palynological Society". The American Association of Stratigraphic Palynologists (AASP)