''Rangea'' is a

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

Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...

fossil with six-fold radial symmetry. It is the type genus of the

rangeomorphs The rangeomorphs are a group of Ediacaran fossils. Ediacarans are the oldest large fossil organisms on earth, and many are not self-evidently related to anything else that has ever lived. However, some Ediacarans clearly resemble each other. Pale ...

. ''Rangea'' was the first complex Precambrian macrofossil named and described anywhere in the world. ''Rangea'' was a centimetre- to decimetre-scale frond characterised by a repetitive pattern of self-similar branches and a sessile benthic lifestyle. Fossils are typically preserved as moulds and casts exposing only a leafy petalodium, and the rarity and incompleteness of specimens has made it difficult to reconstruct the three-dimensional (3D) morphology of the entire organism.Sharp, Alana C., Alistair R. Evans, Siobhan A. Wilson, and Patricia Vickers-Rich. "First Non-destructive Internal Imaging of Rangea, an Icon of Complex Ediacaran Life." Precambrian Research 299 (2017): 303-08. doi: 10.1016/j.precamres.2017.07.023 Fossilized ''Rangea'' consists of several vanes. Each vane has a foliate shape with a series of recessed furrows that run outwards at varying angles from a prominent smooth median zone to define a series of chevron-like units called quilts. The quilts are arranged in two rows, that is, as long petaliform primary quilts and short lanceolate subsidiary quilts. The subsidiary quilts pinch out a short distance from the median zone as the primary quilts expand whereas the primary quilts extend to the edge of the frond where they taper bluntly. In no specimen can an exact total of primary quilts be counted, on account of either missing areas or incomplete preservation. The apices of the quilts are sharply delimited by wedge-shaped fields of either smooth or wrinkled relief that give this part of the body a scalloped appearance.Grazhdankin, Dima, and Adolf Seilacher. "A Re-examination of the Nama-type Vendian Organism Rangea Schneiderhoehni." Geological Magazine 142.5 (2005): 571-82. . doi:10.1017/S0016756805000920 Rangea scheiderhoehni 3

A total of six species have been described, but only the type species ''Rangea schneiderhoehoni'' is considered valid: * ''R. brevior'' Gürich 1933 = ''R. schneiderhoehoni''. * ''R. arborea'' Glaessner, 1959 = ''

Arborea Arborea is a town and ''comune'' in the province of Oristano, Sardinia, Italy, whose economy is largely based on agriculture and cattle breeding with production of vegetables, rice, fruit and milk (notably the local milk product Arborea). Histo ...

arborea''. * ''R. grandis'' Glaessner et Wade, 1966 = ''Glassnerina grandis'' = ''

Charnia ''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 (thus exhibiting glide reflection, or opposite is ...

massoni''. * ''R. longa'' Glaessner et Wade, 1966 = ''Akrophyllas longa''. * ''R. sibirica'' Sokolov, 1972 = ''Charnia sibirica'' = ''Charnia massoni''. ''Rangea schneiderhoehni'' fossils have been found in the Kanies and Kliphoek Members of the Dabis Formation and in the Niederhagen Member of the Nudaus Formation,

Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

. These deposits date from around 548 Mya. ''Rangea'' fossils have also been reported from the Ediacaran deposits of the

Arkhangelsk region Arkhangelsk Oblast ( rus, Архангельская область, p=ɐrˈxanɡʲɪlʲskəjə ˈobɫəsʲtʲ) is a federal subject of Russia (an oblast). It includes the Arctic archipelagos of Franz Josef Land and Novaya Zemlya, as well as t ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

and in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. These fossils date from around 558-555 Mya. ''Rangea'' seems to have led a

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 ...

existence. New specimens provide evidence that ''Rangea'' was not a simple flexuous frond but a squat obconical fossil with radiating vanes which conjoin in a rather precise manner, so that the ridges corresponding to the axial traces on the branches on the reverse side of one frond exactly fit the depressions between the branches on the reverse side of the next, and the distal ends of the individual fronds meet virtually at a point. If the whole ''Rangea'' specimen is curved or deformed, then the same kind of curvature influences all its individual vanes. In one specimen, narrow wedges of sediment about 1–2 mm thick and some 5–6 mm deep penetrate the sutures between adjacent, conjoined fronds. This suggests that though it is usual for the lateral parts of the fronds to be tightly appressed and composite molded together, the individual fronds of the live organism were discrete structures, either largely or completely separate from those adjacent. The highly ordered, complex branching of the structural elements of the frond is a common characteristic and possibly reflects an unusual environmental parameter in early Ediacaran seas. Rangea scheiderhoehni 2

''Rangea'' likely had a rigid or semi-rigid skeleton-like structure that prevented buckling or compression and maintained integrity during life. Ediacaran-style preservation is thought to have been aided by microbial mats that covered the sea floor. The high abundance of quartz found within these specimens is consistent with infilling of the organism by detrital quartz and preservation in sandstone. Another peculiarity of ''Rangea'' is the clustering of several vanes into a closely packed compound structure. In each cluster all the constituent fronds demonstrate a similarity in quilt morphology and uniformity of quilt arrangement. Furthermore, these clusters maintain their integrity in winnowed specimens of Rangea. This implies certain stability and resistance of the cluster to mechanical stress. ''Rangea'' is reconstructed as an immobile benthic creature, whose body consisted of three closely packed trough-shaped fronds enveloped by a mucous sheath. Three-dimensional preservation and biostratinomy of the fossils suggest that in life ''Rangea'' was completely immersed into sand, and that the sand filled the cavities of the trough-shaped fronds. Living ''Rangea'' had a convex-down posture within the sediment, with the edges of all three vanes rising above sediment. Each frond consisted of two membranes, and the space between these membranes was inflated and fractally quilted. The quilts were probably hydrostatically supported. Composite moulding of the frond suggests that the quilt boundaries correspond to structures stiff enough to press through the integument.

Gregory Retallack Gregory John Retallack (born 8 November 1951) is an Australian paleontologist, geologist, and author who specializes in the study of fossil soils ( paleopedology). His research has examined the fossil record of soils though major events in Earth ...

considered that ''Rangea'' is not a benthic shallow marine fossil comparable with a sea pen but an alga or fungus from tidal flat or fluvial environments, however his theory about Ediacaran biota is controversial.

See also

References

Further reading