Aspidella

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Aspidella is also a homonym for the mushroom genus Saproamanita.

Aspidella
Temporal range: Tonian to Ediacaran, 850–555 Ma
Aspidella surface.jpg
Aspidella individuals on a bedding plane in the Fermeuse Formation, Newfoundland
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia (?)
Genus:† Aspidella
Billings, 1872
Species:
†A. terranovica
Binomial name
†Aspidella terranovica
Billings, 1872
Synonyms

Possibly numerous, see text.

Aspidella is an Ediacaran disk-shaped fossil of uncertain affinity. It is known from the single species A. terranovica. [1]

Contents

Morphology

Aspidella consists of disk-shaped fossils, with concentric rings and/or centripetal rays. The diameter of circular Aspidella varies from 1 to 180 mm. [1] Most individuals are between 4 and 10 mm, but smaller individuals would presumably have decayed before they could fossilize. Other Aspidella take the form of ellipses, 3–8 cm long and 1–4 cm wide. Most have a central pimple. The rim of all specimens is made up by ridge-edged rays and/or concentric rings.

Ecology

Large and small Aspidella discs on a bedding surface of the Fermeuse Formation Large Aspidella.jpg
Large and small Aspidella discs on a bedding surface of the Fermeuse Formation

The rarity of large individuals probably indicates that Aspidella were r-strategists, producing numerous offspring of which most died young. It is most common in deep-water sediments, but is a constituent of most Ediacaran fossil assemblages, including those deposited above storm wave-base. [2] The organisms can reach densities of more than 3000 per square meter. [2]

Affinity

Just like Ediacaria (see also below), Aspidella has initially been considered a scyphozoan jellyfish. This initial designation has been refuted; some specimens have been shown to be the holdfast of some organism, the main body of which extended into the open water but broke off before fossilization (a few specimens bearing stubs of stalks opposed to the central pimple support this); [3] [4] whereas others represent microbial colonies. [5]

Some individuals are associated with movement trails resembling those produced by modern sea anemones (Cnidaria). [6]

Taphonomy

The upper and lower surfaces of the fossils have a distinct elemental composition that resembles that of fossilized biofilms. [2] The sediment within the fossils also has a distinct composition, being enriched in certain elements with respect to the rock matrix. Since it is difficult to account for such a distribution of elements by post-mortem diagenetic processes, it would appear that the elements (and thus the sediment) were incorporated into the organism whilst it was alive. [2]

History of research

Aspidella terranovica was first discovered in 1868 by Scottish geologist Alexander Murray. [7] In 1872, Elkanah Billings described Aspidella terranovica fossils from Duckworth Street, St. John's, Newfoundland ( 47°34′01.3″N52°42′18.3″W / 47.567028°N 52.705083°W / 47.567028; -52.705083 (Aspidella) ). [8] They are preserved in a Neoproterozoic outcrop of black shale. Billings was the head paleontologist with the Geological Survey of Canada at the time. Even so, his findings were questioned by Charles Doolittle Walcott, who quoted opinion that the shapes in the rocks were concretions formed inorganically. [9] Other explanations offered at the time were that the circles were gas escape bubbles, or fakes planted by God to lure those with little faith into error[ citation needed ]. They were the first Ediacaran (Vendian) fossils described by a scientist.

For decades, Aspidella and its partner fossils were not considered to be Precambrian life forms. This lasted until the work of Reg Sprigg, who discovered the Ediacara Hills fossils. [10] Fossils were found in many other parts of the world in rocks of about the same age and became accepted as genuine remains of life forms.

Systematics and taxonomy

1-2 centimetre-wide Aspidella discs (and some smaller mm-sized individuals) on a bedding surface of the Fermeuse Formation near Ferryland, Newfoundland Aspidella specimens.jpg
1-2 centimetre-wide Aspidella discs (and some smaller mm-sized individuals) on a bedding surface of the Fermeuse Formation near Ferryland, Newfoundland
Artists interpretation of the rare Taphomorph of Aspidella, Wigwamiella enigmatica Wigwamiella.png
Artists interpretation of the rare Taphomorph of Aspidella, Wigwamiella enigmatica

Aspidella is derived from the Latin diminutive of Ancient Greek aspis (Ασπις, a round shield), and terranovica is Latin for "from the new land" (i.e. Newfoundland).

Different morphological forms have been called Ediacaria or Spriggia. However, the differences between the small elliptical "typical" Aspidella, the flat, ringed Spriggia wadea and the large, pimpled, and rayed Ediacaria seem to be due to different taphonomic conditions. For example, Spriggia and Ediacaria appear to be remains of the same animals, only that the former was fossilized in more compact, fine-grained clay, whereas the latter is known from rocks that originally were predominantly sandy sediment.[ citation needed ]

Numerous other taxa may also be junior synonyms of Aspidella:

Due to its nondescript nature, Aspidella might be considered a form taxon, an artificial assemblage of similar-looking and similar-living organisms without a phylogenetic relationship. In this case, some presumed synonyms (such as Ediacaria or Cyclomedusa) would remain valid. The type specimens were of the ellipsoid type (they are lost, but a cast remains). Thus, if Aspidella in the loose sense turns out to be an assemblage of more or less related taxa, the genus name would apply only to the smallish ellipsoid specimens. Regardless of its ultimate classification, because it has been classified as either an animal, or a plant (alga), or a fungus (lichen), the name Aspidella is covered by both Codes of Nomenclature, and this prevents adoption of a later homonym "Aspidella" (Gilbert 1940) for a group of extant mushrooms, now renamed Saproamanita . [11]

Occurrence

Other locations where Aspidella specimens are reported include the Bonavista Peninsula and Mistaken Point in Newfoundland, the Twitya Formation in British Columbia, and central North Carolina. [12]

Aspidella fossils are found from 610 to 555 million years ago, with putative representatives dating to 770  million years ago. [13]

More recently, Aspidella fossils have been found in the mid-Tonian-aged Heavitree Formation, Amadeus Basin, Central Australia, dated to ~ 850  million years ago. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

<span class="mw-page-title-main">Neoproterozoic</span> Third and last era of the Proterozoic Eon

The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era of the Phanerozoic eon, and is further subdivided into three periods, the Tonian, Cryogenian and Ediacaran.

<i>Pteridinium</i> Ediacaran fossil

Pteridinium is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota.

<i>Dickinsonia</i> Extinct genus of early animals

Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. It lived during the late Ediacaran. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.

<i>Cyclomedusa</i> Extinct genus of aquatic animals

Cyclomedusa is a circular fossil of the Ediacaran biota; it has a circular bump in the middle and as many as five circular growth ridges around it. Many specimens are small, but specimens in excess of 20 cm are known. The concentric disks are not necessarily circular, especially when adjacent individuals interfere with each other's growth. Many radial segment lines — somewhat pineapple-like — extend across the outer disks. A few specimens show what might be a stem extending from the center in some direction or other.

<i>Charnia</i> Genus of frond-like lifeforms

Charnia is an extinct genus of frond-like lifeforms belonging to the Ediacaran biota with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture. The genus Charnia was named after Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found. Charnia is significant because it was the first Precambrian fossil to be recognized as such.

<span class="mw-page-title-main">Rangeomorph</span> Form taxon of frondose Ediacaran fossils

The rangeomorphs are a form taxon of frondose Ediacaran fossils that are united by a similarity to Rangea. Some researchers, such as Pflug and Narbonne, suggest that a natural taxon Rangeomorpha may include all similar-looking fossils. Rangeomorphs appear to have had an effective reproductive strategy, based on analysis of the distribution pattern of Fractofusus, which consisted of sending out a waterborne asexual propagule to a distant area, and then spreading rapidly from there, just as plants today spread by stolons or runners.

<i>Tribrachidium</i> Extinct genus of invertebrates

Tribrachidium heraldicum is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. T. heraldicum is the best known member of the extinct group Trilobozoa.

<span class="mw-page-title-main">Vendobionta</span> Group of extinct creatures that were part of the Ediacaran biota

Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

<i>Ediacaria</i> Genus of cnidarians

Ediacaria is a fossil genus dating to the Ediacaran Period of the Neoproterozoic Era. Unlike most Ediacaran biota, which disappeared almost entirely from the fossil record at the end of the Period, Ediacaria fossils have been found dating from the Baikalian age of the Upper Riphean to 501 million years ago, well into the Cambrian Period. Ediacaria consists of concentric rough circles, radial lines between the circles and a central dome, with a diameter from 1 to 70 cm.

<i>Rangea</i> Fossil taxon

Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.

<span class="mw-page-title-main">Stratigraphy of the Cambrian</span>

The Stratigraphy of the Cambrian period currently has several schemes used for ordering geologic formations from the period. The International Commission on Stratigraphy−ICS scheme has set a stratotype section for the base of the Cambrian, dated quite accurately to 538.8 ± 0.2 million years ago. Russian and Chinese scientists have developed a different scheme.

<i>Arumberia</i> Trace fossil

Arumberia is an enigmatic fossil from the Ediacaran period originally described from the Arumbera Sandstone, Northern Territory, Australia but also found in the Urals, East Siberia, England and Wales, Northern France, the Avalon Peninsula and India. Several morphologically distinct species are recognized.

<span class="mw-page-title-main">Fermeuse Formation</span>

The Fermeuse Formation is a fossil-bearing Ediacaran geologic formation in Newfoundland.

<i>Parviscopa</i> Genus of frondose

Parviscopa is a genus of frondose forms characterized in 2008 based on specimens from Newfoundland, Canada. Parviscopa is a member of the Ediacaran biota, and is more specifically part of the Avalon type assemblage, which is from the older part of the Ediacaran and is characterized by deep water deposits.

<i>Medusinites</i> Extinct genus of cnidarians

Medusinites is a genus of disc shaped fossilised organisms associated with the Ediacaran biota. They have been found in rocks dated to be 580 to 541 million years old.

<i>Hapsidophyllas</i> Ediacaran rangeomorph fossil Hapsidophyllas flexibilis

Hapsidophyllas is a rare Ediacaran rangeomorph fossil found at Mistaken Point, Newfoundland, Canada. It was first identified by Emily Bamforth and Guy Narbonne in 2009. Because its characteristic flexible leaflet structure is dissimilar to other known rangeomorphs, Bamforth and Narbonne describe it as a new rangeomorph form, called hapsidophyllid. The only other known hapsidophyllid is the Ediacaran frond Frondophyllas grandis, which shares the network-like configuration of leaflets seen in Hapsidophyllas. Currently, the Hapsidophyllas flexibilis holotype resides in its type locality in the Mistaken Point Ecological Reserve, and a cast of the specimen is on display at the Royal Ontario Museum in Toronto, Canada.

References

  1. 1 2 Peterson. P. 131
  2. 1 2 3 4 Laflamme, M.; Schiffbauer, J. D.; Narbonne, G. M.; Briggs, D. E. G. (2010). "Microbial biofilms and the preservation of the Ediacara biota". Lethaia. 44 (2): 203–213. doi:10.1111/j.1502-3931.2010.00235.x.
  3. ↑ Narbonne, G. M. (2005). "THE EDIACARA BIOTA: Neoproterozoic Origin of Animals and Their Ecosystems". Annual Review of Earth and Planetary Sciences. 33: 421–442. Bibcode:2005AREPS..33..421N. doi:10.1146/annurev.earth.33.092203.122519.
  4. ↑ MacGabhann, B. A. (2007). "Discoidal fossils of the Ediacaran biota: a review of current understanding". Geological Society, London, Special Publications. 286 (1): 297–313. Bibcode:2007GSLSP.286..297M. doi:10.1144/SP286.21. S2CID   129521521.
  5. ↑ GRAZHDANKIN, D.; GERDES, G. (2007). "Ediacaran microbial colonies". Lethaia. 40 (3): 201–210. doi:10.1111/j.1502-3931.2007.00025.x. Archived from the original on 2013-01-05.
  6. ↑ Evidence for Cnidaria-like behavior in ca. 560 Ma Ediacaran Aspidella Article in Geology 41:895-898 · February 2013
  7. ↑ See:
  8. ↑ Billings, E. (1872). "On some fossils from the primordial rocks of Newfoundland". The Canadian Naturalist. 2nd series. 6 (4): 465–479. ; see p. 478.
  9. ↑ Walcott, Charles D. (6 April 1899). "Pre-Cambrian fossiliferous formations". Bulletin of the Geological Society of America. 10 (1): 199–244. Bibcode:1899GSAB...10..199W. doi:10.1130/GSAB-10-199. hdl: 2027/hvd.32044107306292 . On p. 231, Walcott quotes "Mr. G.F. Matthew, of Saint John, New Brunswick": "I have seen Aspidella terranovica in the museum at Ottawa and doubt its organic origin. It seems to me a slickensided mud concretion striated by pressure."
  10. ↑ Sprigg, Reg. C. (1947). "Early Cambrian (?) jellyfishes from the Flinders Ranges, South Australia". Transactions of the Royal Society of South Australia. 71 (2): 212–224.
  11. ↑ Redhead SA, Vizzini A, Drehmel DC, Contu M (2016). "Saproamanita, a new name for both Lepidella E.-J. Gilbert and Aspidella E.-J. Gilbert (Amaniteae, Amanitaceae)". IMA Fungus. 7 (1): 119–129. doi:10.5598/imafungus.2016.07.01.07. PMC   4941681 . PMID   27433443.
  12. ↑ Hibbard, J. P.; Pollock, J. C.; Brennan, M.; Samson, S. D.; Secor, D. (2009). "Significance of New Ediacaran Fossils and U‐Pb Zircon Ages from the Albemarle Group, Carolina Terrane of North Carolina". The Journal of Geology. 117 (5): 487–498. Bibcode:2009JG....117..487H. doi:10.1086/600863. S2CID   129184707.
  13. ↑ Meert, J. G.; Gibsher, A. S.; Levashova, N. M.; Grice, W. C.; Kamenov, G. D.; Rybanin, A. (2010). "Glaciation and ~770 Ma Ediacara (?) Fossils from the Lesser Karatau Microcontinent, Kazakhstan". Gondwana Research. 19 (4): 867–880. Bibcode:2011GondR..19..867M. doi:10.1016/j.gr.2010.11.008.
  14. ↑ Plummer, P. S.; Gorter, J. D. (2023). "Aspidella and Water Escape Structures from the ca 850 Ma (Tonian) Heavitree Formation, Amadeus Basin, Central Australia". Australian Journal of Earth Sciences. doi:10.1080/08120099.2023.2290248.
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