Charnia is a genus of frond-like Ediacaran lifeforms 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. 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 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:
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 at varying levels of decay; these include the IvesheadiomorphsIvesheadia, Blackbrookia, Pseudovendia and Shepshedia.
Charnia masoni was brought to the attention of scientists by Roger Mason, a schoolboy who later became a professor of metamorphicpetrology. In 1957 Mason and his friends were rock-climbing in Charnwood Forest, 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, a local geologist. Mason took Ford to the site; Ford wrote up the discovery in the Journal of the Yorkshire Geological Society. The holotype now resides, along with a cast of its sister taxonCharniodiscus, in New Walk Museum & Art Gallery, Leicester. 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 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 and the 1940s 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, it was reinterpreted as a sea pen 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 increasingly popular theory has arisen since the mid-1980s, following the work of Adolf Seilacher who suggested that Charniabelongs 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 anything else. This new group was termed the Vendobionta, 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 New Walk Museum. 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 and sessile, anchored to the sea floor. According to one currently popular hypothesis, it probably lived in deep waters, well below the wave base, thus placing it out of range of photosynthesis. Furthermore, it has no obvious feeding apparatus so its lifestyle remains enigmatic. Some have speculated that it survived either by filter feeding or directly absorbing nutrients, and this is currently the focus of considerable research. 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, which grow by basal insertion, Charnia grew by the apical insertion of new buds.
