''Charnia'' is a
genus of
frond
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
-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 (thus exhibiting
glide reflection
In 2-dimensional geometry, a glide reflection (or transflection) is a symmetry operation that consists of a reflection over a line and then translation along that line, combined into a single operation. The intermediate step between reflecti ...
, or opposite isometry). The genus ''Charnia'' was named after
Charnwood Forest
Charnwood Forest is a hilly tract in north-western Leicestershire, England, bounded by Leicester, Loughborough and Coalville. The area is undulating, rocky and picturesque, with barren areas. It also has some extensive tracts of woodland; ...
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.
The living organism grew on the sea floor and is believed to have fed on nutrients in the water. Despite ''Charnia'' fern-like appearance, it is not a photosynthetic plant or alga because the nature of the fossilbeds where specimens have been found implies that it originally lived in deep water, well below the
photic zone
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological pro ...
where
photosynthesis can occur.
Diversity
Several ''Charnia'' species were described but only the type species ''C. masoni'' is considered valid. Some specimens of ''C. masoni'' were described as members of genus ''Rangea'' or a separate genus ''Glaessnerina'':
* ''
Rangea grandis'' Glaessner & Wade, 1966
= ''Glaessnerina grandis''
* ''Rangea sibirica'' Sokolov, 1972 = ''Glaessnerina sibirica''
Two other described ''Charnia'' species have been transferred to two separate genera
* ''Charnia wardi'' Narbonne & Gehling, 2003
transferred to the genus ''
Trepassia'' Narbonne et al., 2009
* ''Charnia antecedens'' Laflamme et al., 2007
transferred to the genus ''
Vinlandia'' Brasier, Antcliffe & Liu, 2012
A number of Ediacaran form taxa are thought to represent ''Charnia'' (or ''
Charniodiscus
''Charniodiscus'' is an Ediacaran fossil that in life was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The ...
'') at varying levels of decay; these include the
Ivesheadiomorphs ''
Ivesheadia
The "ivesheadiomorphs" are a group of fossilised structures known from Ediacaran localities in England and Newfoundland. They are considered to be taphomorphs, representing the poorly preserved biological remains of various contemporary taxa such ...
'', ''
Blackbrookia
The "ivesheadiomorphs" are a group of fossilised structures known from Ediacaran localities in England and Newfoundland. They are considered to be taphomorphs, representing the poorly preserved biological remains of various contemporary taxa such ...
'', ''
Pseudovendia'' and ''
Shepshedia''.
Distribution
''Charnia masoni'' was first described from the
Maplewell Group in
Charnwood Forest
Charnwood Forest is a hilly tract in north-western Leicestershire, England, bounded by Leicester, Loughborough and Coalville. The area is undulating, rocky and picturesque, with barren areas. It also has some extensive tracts of woodland; ...
in England and subsequently was found in
Ediacara Hills in Australia,
Siberia and White Sea area in Russia and Precambrian deposits in Newfoundland, Canada.
It lived around 570-550 million years ago.
Discovery
''Charnia masoni'' was brought to the attention of scientists by Roger Mason, a schoolboy who later became a professor of metamorphic petrology
Petrology () is the branch of geology that studies rock (geology), rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly ...
. In 1957 Mason and his friends were rock-climbing in Charnwood Forest
Charnwood Forest is a hilly tract in north-western Leicestershire, England, bounded by Leicester, Loughborough and Coalville. The area is undulating, rocky and picturesque, with barren areas. It also has some extensive tracts of woodland; ...
, in what is now a protected fossil site in Central England. They noticed this unusual fossil, and Mason took a rubbing of the rock. He showed the rubbing to his father, the minister of Leicester's Great Meeting Unitarian Chapel, who also taught at the local university and knew Trevor Ford
Trevor Ford (1 October 1923 – 29 May 2003) was a Welsh professional footballer who played as a centre forward for Swansea Town, Aston Villa, Sunderland, Cardiff City, PSV, Newport County and Romford, as well as for the Wales national team ...
, a local geologist. Mason took Ford to the site; Ford wrote up the discovery in the ''Journal of the Yorkshire Geological Society''.
The holotype (the actual physical example from which the species was first described) now resides, along with a cast of its sister taxon ''Charniodiscus
''Charniodiscus'' is an Ediacaran fossil that in life was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The ...
'', in Leicester Museum & Art Gallery
The Leicester Museum & Art Gallery (until 2020, New Walk Museum and Art Gallery) is a museum on New Walk in Leicester, England, not far from the city centre. It opened in 1849 as one of the first public museums in the United Kingdom. Leicest ...
. Decades later it came to light that Tina Negus, then a 15-year-old schoolgirl, had seen this fossil a year before the boys but her geography schoolteacher discounted the possibility of Precambrian fossils. Mason acknowledges, and the museum's Charnia display explains, that the fossil had been discovered a year earlier by Negus, "but no one took her seriously". She was recognised at the 50th anniversary celebrations of the official discovery.
Significance
''Charnia'' is known from specimens as small as only , up to the largest specimens of in length. It is a highly significant fossil because it is the first fossil which was ever described to have come from undoubted Precambrian rocks. Prior to 1958, the Precambrian was thought to be completely devoid of fossils and consequently possibly devoid of macroscopic life. Similar fossils had been found in the 1930s (in Namibia) and the 1940s (in Australia) but these forms were assumed to be of Cambrian age and were therefore considered unremarkable at the time. ''Charnia'' has become an enduring image of Precambrian animals. Originally interpreted as an alga
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
, it was reinterpreted as a sea pen
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described species, around 200 are valid. Sea pens have a cosm ...
(a sister group to the modern soft corals
Alcyonacea, or soft corals, are an order of corals. In addition to the fleshy soft corals, the order Alcyonacea now contains all species previously known as "gorgonian corals", that produce a more or less hard skeleton, though quite different ...
) from 1966 onwards. Acceptance of ''Charnia'' as a Precambrian lifeform led to recognition of other major Precambrian animal groups, although the sea pen interpretation of ''Charnia'' has recently been discredited, and the current "state of the art" is something of a "statement of ignorance".
An alternative theory has arisen since the mid-1980s, following the work of Adolf Seilacher
Adolf "Dolf" Seilacher (February 24, 1925 – April 26, 2014) was a German palaeontologist who worked in evolutionary and ecological palaeobiology for over 60 years. He is best known for his contributions to the study of trace fossils; constructi ...
who suggested that ''Charnia'' belongs to an extinct group of unknown grade which was confined to the Ediacaran Period. This suggests that almost all the forms that have been postulated to be members of many and various modern animal groups are actually more closely related to each other than they are to anything else. This new group was termed the Vendobionta
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 w ...
,[Seilacher, A. 1984. Late Precambrian and Early Cambrian Metazoa: preservational or real extinctions? 159–168. In Holland, H. D., Trendal, A. F. and Bernhard,
S. (eds). ''Patterns of Change in Earth Evolution''. Springer Verlag, New York, NY, 450 pp.] a clade whose position in the tree of life is unclear, perhaps united by its construction via unipolar iterations of one cell family.
The holotype is a star attraction at the Leicester Museum & Art Gallery. A day-long seminar in 2007 devoted to ''Charnia'' called it "Leicester's fossil celebrity".
Ecology
Little is known about the ecology of ''Charnia''. It was benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
and sessile
Sessility, or sessile, may refer to:
* Sessility (motility), organisms which are not able to move about
* Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant
* Sessility (medicine), tumors and polyps that ...
, anchored to the sea floor. According to one currently popular hypothesis, it probably lived in deep waters, well below the wave base
The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. At water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion ab ...
, thus placing it out of range of photosynthesis. Furthermore, it has no obvious feeding apparatus ( mouth, gut, etc.) so its lifestyle remains enigmatic. Some have speculated that it survived either by filter feeding
Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...
or directly absorbing nutrients, and this is currently the focus of considerable research.[Narbonne]
The growth and development of the Ediacara biota is also a subject of continued research, and this has discredited the sea pen hypothesis. In contrast to sea pens
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described species, around 200 are valid. Sea pens have a cosm ...
, which grow by basal insertion, ''Charnia'' grew by the apical insertion of new buds.[
]
See also
* List of Ediacaran genera
This is a list of all described Ediacaran genera, including the Ediacaran biota. It contains 227 genera.
References
{{reflist, 30em
*
Ediacaran
The Ediacaran Period ( ) is a geological period that spans 96 million years from the end ...
* ''Charniodiscus
''Charniodiscus'' is an Ediacaran fossil that in life was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. The ...
''
References
External links
An article on the discovery of ''Charnia masoni'':
*https://web.archive.org/web/20070510112737/http://www.charnia.org.uk/newsletter/brit_assoc_2002.htm
A write-up of the discovery, with Charnia art by Tina Negus
{{Taxonbar, from=Q134755
Ediacaran life
Rangeomorpha
Charniidae
Ediacaran Europe