Rangeomorph
Encyclopedia
The Rangeomorphs are a form taxon
of frondose Ediacaran
fossils that are united by a similarity to Rangea
. Some workers, e.g. Pflug and Narbonne, suggest that a natural taxon
Rangeomorpha may include all similar-looking fossils.
Rangeomorphs are a key part of the Ediacaran biota which survived about 30 million years, until the base of the Cambrian
. They were especially abundant in early Ediacaran Mistaken Point assemblage found in Newfoundland.
ity, and could have been formed using fairly simple developmental patterns.
) lay flat on the sediment surface.
which establishes the rangeomorph clade as a valid taxonomic entity. The quilted construction suggests a close affinity to the erniettomorph
s.
Form taxon
Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships...
of frondose Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
fossils that are united by a similarity to Rangea
Rangea
Rangea is a frond-like fossil of the Ediacaran period.The features found in Rangea are a double-layered quilted structure, a tripartite stemless body with fourfold radial symmetry, a mucous-supported sheath, smooth surface, radial membranes, and internal organs that are a system of sacs connected...
. Some workers, e.g. Pflug and Narbonne, suggest that a natural taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
Rangeomorpha may include all similar-looking fossils.
Rangeomorphs are a key part of the Ediacaran biota which survived about 30 million years, until the base of the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
. They were especially abundant in 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 itself composed of many smaller branching tubes held up by a semi-rigid organic skeleton. This self-similar structure proceeds over four levels of fractalFractal
A fractal has been defined as "a rough or fragmented geometric shape that can be split into parts, each of which is a reduced-size copy of the whole," a property called self-similarity...
ity, and could have been formed using fairly simple developmental patterns.
Ecology
Rangeomorphs dwelt mainly in the deep ocean, were unable to move, and had no apparent reproductive organs, perhaps reproducing asexually by dropping off new fronds. Nor is there evidence of a gut or mouth. This has led to the hypothesis that they gathered nutrients from seawater by osmosis. Most were attached to the sea floor by a stalk or holdfast, although others (such as the spindle-shaped FractofususFractofusus
Fractofusus misrai is a fossil discovered in Newfoundland, Canada.- Discovery of vendian fossils in the Avalon Peninsula :In the summer of 1967, S.D.Misra an Indian graduate student at Newfoundland's Memorial University discovered a rich assemblage of imprints of soft bodied organisms on the...
) 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 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 apomorphySynapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
which establishes the rangeomorph clade as a valid taxonomic entity. The quilted construction suggests a close affinity to the erniettomorph
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 and possibly Dickinsonia....
s.