The rangeomorphs are a

form taxon Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of s ...

frondose Frondosity (from Latin ''frondōsus'' meaning 'leafy') is the property of an organism that normally flourishes with fronds or leaf-like structures. Many frondose organisms are thalloid and lack the organization of tissues into organs, with the ...

Ediacaran fossils that are united by a similarity to ''

Rangea ''Rangea'' is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs. ''Rangea'' was the first complex Precambrian macrofossil named and described anywhere in the world. ''Rangea'' was a centimetre- ...

''. Some researchers, such as Pflug and Narbonne, suggest that a natural

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

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 misrai ''Fractofusus misrai'' is an Ediacaran fossil discovered in 1967 by S.B. Misra at Mistaken Point, Newfoundland and Labrador, Canada, which has since become the Mistaken Point Ecological Reserve. It was named after Professor Misra in 2007. It ...

'', which consisted of sending out a waterborne asexual

propagule In biology, a propagule is any material that functions in propagating an organism to the next stage in its life cycle, such as by dispersal. The propagule is usually distinct in form from the parent organism. Propagules are produced by organisms ...

to a distant area, and then spreading rapidly from there, just as plants today spread by stolons or runners. Rangeomorphs are a key part of the Ediacaran biota, which survived about 30 million years, until the base of the Cambrian, which was . They were especially abundant in the early Ediacaran Mistaken Point assemblage found in Newfoundland.

Body plan

Rangeomorphs consist of branching "frond" elements, each a few centimetres long, each of which is composed of many smaller branching tubes held up by a semi-rigid organic skeleton. This self-similar structure proceeds over four levels of fractality, and could have been formed using fairly simple developmental patterns.

Ecology

Rangeomorphs dwelt in shallow to abyssal marine environments, were unable to move, and had no apparent reproductive organs. They possibly reproduced asexually by dropping off new fronds. There is little evidence of a gut or mouth, while the organisms have high surface area to volume ratios, which has led to the hypothesis that they gathered nutrients from seawater by

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region o ...

. However, others argue this is implausible and suggest

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 other mechanisms. Most were attached to the sea floor by a stalk or holdfast, although others (such as the spindle-shaped '' Fractofusus'') lay flat on the sediment surface.

Affinity

Rangeomorph communities are similar in structure to those of modern, suspension-feeding animals, but it is difficult to relate their morphology to any modern animals. They have at times been aligned to a range of modern animal and protist groups, but none of these classifications has withstood scrutiny; they probably represent an extinct

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

to either the animals or fungi. Whilst the fractal construction may represent a convergent adaptation to osmotic feeding, most workers now consider it to be an apomorphy which establishes the rangeomorph clade as a valid taxonomic entity. The quilted construction suggests a close affinity to the

erniettomorph The Erniettomorphs are a form of Ediacaran fossil consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include '' Ernietta'', '' Phyllozoon'', ''Pteridinium'', ''Swartpuntia''. Undisputed ...

References

External links

* Jeff Hecht
Fractal patterns of early life revealed
On: New Scientist. 15 July 2004 * Tia Ghose

On: LiveScience. 11 August 2014 – Artist's reconstruction * Brandon Specktor

On: LiveScience. 5 March 2020 {{Taxonbar, from=Q547464 Ediacaran life Incertae sedis Petalonamae