:Aspidella'' is also a
homonym
In linguistics, homonyms are words which are homographs (words that share the same spelling, regardless of pronunciation), or homophones (equivocal words, that share the same pronunciation, regardless of spelling), or both. Using this definition, ...
for the
mushroom
A mushroom or toadstool is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground, on soil, or on its food source. ''Toadstool'' generally denotes one poisonous to humans.
The standard for the name "mushroom" is t ...
genus ''
Saproamanita
The genus ''Saproamanita'' contains about 24 species of agarics and is one of six genera in the family Amanitaceae. The others are ''Amanita'' (which now includes the synonym ''Torrendia'', a generic name previously applied to secotioid, sequestr ...
.
''Aspidella'' is an
Ediacaran
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...
disk-shaped
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
of uncertain affinity. It is known from the single species ''A. terranovica''.
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.
[Peterson. P. 131] 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
ellipse
In mathematics, an ellipse is a plane curve surrounding two focus (geometry), focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special ty ...
s, 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 Aspidella](https://upload.wikimedia.org/wikipedia/commons/0/02/Large_Aspidella.jpg)
The rarity of large individuals probably indicates that ''Aspidella'' were
r-strategist
In ecology, ''r''/''K'' selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus on either an increased quantity of offspring at the expense of individ ...
s, 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.
[ The organisms can reach densities of 3000 m−2.][
]
Affinity
Just like ''Ediacaria
''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 d ...
'' (see also below), ''Aspidella'' has initially been considered a scyphozoa
The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies").
The class name Scyphozoa comes from the Greek word ''skyphos'' (), denoting a kind of drinking cup and alluding to the ...
n 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); whereas others represent microbial colonies.
Some individuals are associated with movement trails resembling those produced by modern sea anemones (Cnidaria).
Taphonomy
The upper and lower surfaces of the fossils have a distinct elemental composition that resembles that of fossilized biofilms. 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.[
]
History of research
''Aspidella terranovica'' was first discovered in 1868 by Scottish geologist Alexander Murray. In 1872, Elkanah Billings
Elkanah Billings (May 5, 1820 – June 14, 1876) is often referred to as Canada's first paleontologist. Billings was born on a farm by the Rideau River outside Bytown (Ottawa), now known as Billings Estate Museum, Billings Estate. His parents w ...
described ''Aspidella terranovica'' fossils from Duckworth Street, St. John's, Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
(). They are in a Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
outcrop of black shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
. Billings was the head paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
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. 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. They were the first Ediacaran
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...
(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. 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
''Aspidella'' is derived from the Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
diminutive
A diminutive is a root word that has been modified to convey a slighter degree of its root meaning, either to convey the smallness of the object or quality named, or to convey a sense of intimacy or endearment. A (abbreviated ) is a word-formati ...
of Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
''aspis
An aspis ( grc, ἀσπίς, plural ''aspides'', ), or porpax shield, sometimes mistakenly referred to as a hoplon ( el, ὅπλον) (a term actually referring to the whole equipment of a hoplite), was the heavy wooden shield used by the infa ...
'' (Ασπις, a round shield), and ''terranovica'' is Latin for "from the new land" (i.e. Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
).
Different morphological forms have been called ''Ediacaria
''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 d ...
'' 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
Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov t ...
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
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
, whereas the latter is known from rocks that originally were predominantly sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of s ...
y sediment.
Numerous other taxa may also be junior synonyms
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
of ''Aspidella'':
*'' Beltanella''
*''Cyclomedusa
''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 di ...
''
*''Eoporpita
''Eoporpita'' is a disc or ellipse-shaped Ediacaran fossil with unsure taxonomy/classification. It is known from its type species, ''Eoporpita'' ''medusa'', the only species within the genus ''Eoporpita''.
Classification debate/interpretations ...
''
*'' Glaessneria''
*'' Irridinitus''
*'' Jampolium''
*'' Madigania''
*'' Medusinites''
*'' Paliella''
*'' Paramedusium''
*'' Planomedusites''
*''Ediacaria
''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 d ...
''
*''Tateana
''Tateana,'' and more specifically ''Tateana inflata'', is a very small, discus-like Ediacaran fossil. Its largest diameter is 6.4 mm long and it is radially symmetrical. It has very defined and thin radial striations. The main body seemed to be ...
''
*'' Tirasiana''
*'' Vendella''
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
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
relationship. In this case, some presumed synonyms (such as ''Ediacaria'' or ''Cyclomedusa'') would remain valid. The type specimen
In biology, a type is a particular wiktionary:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to a ...
s 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
The genus ''Saproamanita'' contains about 24 species of agarics and is one of six genera in the family Amanitaceae. The others are ''Amanita'' (which now includes the synonym ''Torrendia'', a generic name previously applied to secotioid, sequestr ...
''.
Occurrence
Other places where ''Aspidella'' specimens are found is the Bonavista Peninsula
The Bonavista Peninsula is a large peninsula on the east coast of the island of Newfoundland in the Canadian province of Newfoundland and Labrador. It consists of 50 incorporated towns/unincorporated communities which have a population of 12,176 ...
and Mistaken Point
Mistaken Point Ecological Reserve is a wilderness area and a UNESCO World Heritage Site located at the southeastern tip of Newfoundland's Avalon Peninsula in the Canadian province of Newfoundland and Labrador. The reserve is home to the namesak ...
in Newfoundland
Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...
, the Twitya Formation
The Twitya Formation is a geologic formation in Canada’s Northwest Territories. It preserves fossils dating back to the Ediacaran period.
See also
* List of fossiliferous stratigraphic units in Northwest Territories
This is a list of fossili ...
in British Columbia
British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...
, and central North Carolina
North Carolina () is a state in the Southeastern region of the United States. The state is the 28th largest and 9th-most populous of the United States. It is bordered by Virginia to the north, the Atlantic Ocean to the east, Georgia and So ...
.
''Aspidella'' fossils are found from , with putative representatives dating to .
See also
* List of Ediacaran genera
References
*
*
External links
*
*
{{Taxonbar, from=Q3312081
Ediacaran life
Incertae sedis
Ediacaran Canada
Taxa named by Elkanah Billings