Rangeomorph

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Rangeomorph
Temporal range: 635–505  Ma
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Possibly one of the last representatives of the Ediacaran biota.
Charnia.png
Charnia masoni, a rangeomorph
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum:† Petalonamae
Clade:† Rangeomorpha
Hofmann et al., 2008
Subtaxa
Synonyms
  • Charniomorpha

The rangeomorphs are a group of Ediacaran fossils. Ediacarans are the oldest large fossil organisms on earth, and many are not obviously related to anything else that has ever lived. However, some Ediacarans clearly resemble each other. Palentologists have not been able to agree on what else, if anything, is related to these organisms, so Ediacarans are usually classified into groups based on their appearance. These "form taxa" allow scientists to study and discuss Ediacarans when they cannot know what kind of living things they were, or how they were genetically related to each other. Rangeomorphs look roughly like fern fronds or feathers arranged around a central axis; the group is defined as Edicarans with a similar appearance and structure to the genus Rangea . Some researchers, such as Pflug and Narbonne, believe all rangeomorphs were more closely related to each other than to anything else. If true, this would make the group a natural taxon called Rangeomorpha (just as all insects are more closely related to each other than to any non-insects, and therefore are a natural taxon called Insecta).

Contents

Rangeomorphs are a key part of the Ediacaran biota, which survived about 30 million years, until the base of the Cambrian, 538.8  million years ago. They were especially abundant in the cold, deep-ocean environments of the early Ediacaran, as shown in the Mistaken Point assemblage in Newfoundland. [1]

Body plan

Rangeomorphs are fractal and self-similar in form: they are made of branching sections, and each section repeats the same shape as the whole. The body "frond" is formed of branching "frond" elements, each a few centimetres long. Each of these is formed of many smaller "frondlets." Structurally, these are tubes held up by a semi-rigid organic skeleton. This body plan could have been formed using fairly simple developmental patterns. [1]

Ecology

Rangeomorphs dwelt in shallow to abyssal marine environments, [2] were unable to move, and had no apparent reproductive organs. They may have reproduced asexually by dropping fronds. Since many lived below the lowest level of the ocean where sunlight can penetrate, they could not have survived by photosynthesis. There is no evidence of a gut or mouth. One hypothesis is that nutrients from seawater were concentrated in their bodies by osmosis. Among living organisms, only osmotrophic bacteria live in this way, but the fractal branching tube structure of rangeomorphs gave them an unusual amount of surface area for every unit of body volume. This structure may have made it possible for osmotrophic organisms to grow to large sizes [3] [4] However, other researchers argue this way of life is implausible, and suggest filter feeding or other mechanisms. [5]

Most rangeomorphs were attached to the sea floor by a stalk ending in a circular holdfast. Holdfasts were often torn from the frond by wave action or decay before fossilization, and are preserved as separate disc-shaped fossils that were given their own genus names (e.g. Aspidella). [6] Other rangeomorphs (such as the spindle-shaped Fractofusus ) lay flat on the sediment surface. [7]

Though we do not know what rangeomorphs were, aspects of their lives are revealed by the fossil record. In some areas, numbers of fronds of the same genus are found together. Analysis suggests that the genus Fractofusus could reproduce in two ways, first by setting a particle of tissue loose in the ocean to land on the sea floor and develop into a new individual (a "grandparent"), and second, by "grandparents" spreading rapidly with stolons to form surrounding groups of smaller "parent" and "child" fronds, just as modern plants such as strawberries spread by runners. [8] [9]

Fossil assemblages from Newfoundland and the UK reveal that rangeomorphs could live in large groups. At least seven genera are associated with filaments or stolons up to four meters long. These filaments ran across or through the bacterial mats on which Ediacarans lived, connected with the holdfasts (or the center of the body in genera without holdfasts), and at least in some cases, connected individuals together. This evidence suggests rangeomorphs may have fed by absorbing nutrients from the bacterial mats, and might even have been colonial organisms (such as corals are today) rather than groups of unrelated individuals. [10]

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. Early researchers thought they were sea pens (Cnidaria), but examination of well-preserved specimens of Charnia reveals that the branching fronds of rangeomorphs were fundamentally different from sea pens in both anatomy and growth pattern, and the modern consensus is that they are unrelated. [6] Rangeomorphs have at times been assigned to a range of modern animal and protist groups, but none of these classifications has withstood scrutiny; [7] they probably represent an extinct stem group to either the animals or fungi. [1] The fractal construction could be an adaptation to osmotic feeding that evolved independently in different groups, but most paleontologists now consider it to be a basic body characteristic inherited from a shared ancestor, which would mean the rangeomorphs are a natural taxon of organisms more closely related to each other than to anything else. [7] The quilted construction suggests a close affinity to the erniettomorphs, another form taxon of Ediacarans whose bodies were made from sheets of many small tubes.

Related Research Articles

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

<i>Charnia</i> Genus of frond-like lifeforms

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. The genus Charnia was named after Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found; the species name after Roger Mason, a schoolboy who found it. Charnia is significant because it was the first Precambrian fossil to be recognized as such.

<i>Spriggina</i> Extinct genus of animals

Spriggina is a genus of early animals whose relationship to living animals is unclear. Fossils of Spriggina are known from the late Ediacaran period in what is now South Australia. Spriggina floundersi is the official fossil emblem of South Australia; it has been found nowhere else.

<span class="mw-page-title-main">Vendobionta</span> Group of extinct creatures that were part of the Ediacaran biota

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 would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

<i>Charniodiscus</i> Genus of extinct Ediacaran lifeform

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 frond was segmented and had a pointed tip. There were two growth forms: one with a short stem and a wide frond, and another with a long stalk, elevating a smaller frond about 50 centimetres (20 in) above the holdfast. While the organism superficially resembles the sea pens (cnidaria), it is probably not a crown-group animal.

<i>Rangea</i> Fossil taxon

Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the Ediacaran period, the final period of the Proterozoic eon. Evidence suggesting that such a mass extinction occurred includes a massive reduction in diversity of acritarchs, the sudden disappearance of the Ediacara biota and calcifying organisms, and the time gap before Cambrian organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring 550 million years ago and the other 539 million years ago.

<i>Fractofusus misrai</i> Frondose Ediacaran fossil

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 represents a frondose rangeomorph, and its overall body plan shows glide reflection symmetry, which is typical of the clade. It is one of two described species in the genus Fractofusus, the other being Fractofusus andersoni.

<i>Eoandromeda</i> Species of Ediacaran animal

Eoandromeda is an Ediacaran organism consisting of eight radial spiral arms, and known from two taphonomic modes: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation of China, where it is abundant.

Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.

<span class="mw-page-title-main">Erniettomorph</span> Extinct clade of fossils

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 Erniettomorphs were Ediacaran, but the species Erytholus, Rutgersella, and Protonympha, who have by some been included in this group but are by no means clear members, are found through to the Late Devonian. Their affinity is uncertain; they probably form a clade and are most likely a sister group to the rangeomorphs, which bear a similar construction. Placements within the metazoan crown-group have been rebutted, and it is most likely that these peculiar organisms lie in the stem group to the animals. There is no evidence that they possessed a mouth or gut. Because they may have been found in water which was too deep to permit photosynthesis – and in some cases, lived half-buried in sediment, it is speculated that they fed by osmosis from the sea water. Such a lifestyle requires a very high surface area to volume ratio – higher than is observed in fossils. However, this paradox can be resolved if much of the volume of the organisms was not metabolically active. Many Pteridinium fossils are found completely filled with sand; if this sand were present within the organism while it was alive, this would reduce its metabolically active volume enough to make osmotic feeding viable.

Avalofractus abaculus is a frond-like rangeomorph fossil described from the Ediacaran of the Trepassey Formation, Spaniard's Bay, Newfoundland.

<span class="mw-page-title-main">Precambrian body plans</span> Structure and development of early multicellular organisms

Until the late 1950s, the Precambrian was not believed to have hosted multicellular organisms. However, with radiometric dating techniques, it has been found that fossils initially found in the Ediacara Hills in Southern Australia date back to the late Precambrian. These fossils are body impressions of organisms shaped like disks, fronds and some with ribbon patterns that were most likely tentacles.

<i>Parviscopa</i> Genus of frondose

Parviscopa is a genus of frondose forms characterized in 2008 based on specimens from Newfoundland, Canada. Parviscopa is a member of the Ediacaran biota, and is more specifically part of the Avalon type assemblage, which is from the older part of the Ediacaran and is characterized by deep water deposits.

<span class="mw-page-title-main">Frondose</span> Property of organism shaped like a frond

Frondosity is the property of an organism that normally flourishes with fronds or leaf-like structures.

<i>Trepassia</i> Extinct species of disc-shaped organism

Trepassia is a 579 million-year-old fossil of Ediacaran rangeomorph. It was first discovered by Guy M. Narbonne, a professor at Queen's University in Ontario, Canada and colleagues in 2009. Three years later, Martin D. Brasier added additional description to Trepassia. The generic name is taken from the French word, trépassés, which translates to "those that have departed forever" and honors the Trepassey community in Newfoundland. It was originally described as Charnia wardi; it was referred under this synonym in a 2016 paper.

Hadrynichorde is a frondose organism from the Ediacaran period discovered in Newfoundland, Canada. It is a sessile, benthic marine organism. resembling modern sea whips.

<i>Hapsidophyllas</i> Ediacaran rangeomorph fossil Hapsidophyllas flexibilis

Hapsidophyllas is a rare Ediacaran rangeomorph fossil found at Mistaken Point, Newfoundland, Canada. It was first identified by Emily Bamforth and Guy Narbonne in 2009. Because its characteristic flexible leaflet structure is dissimilar to other known rangeomorphs, Bamforth and Narbonne describe it as a new rangeomorph form, called hapsidophyllid. The only other known hapsidophyllid is the Ediacaran frond Frondophyllas grandis, which shares the network-like configuration of leaflets seen in Hapsidophyllas. Currently, the Hapsidophyllas flexibilis holotype resides in its type locality in the Mistaken Point Ecological Reserve, and a cast of the specimen is on display at the Royal Ontario Museum in Toronto, Canada.

Hylaecullulus fordi, also described as dumbbells, is an extinct species of Ediacaran petalonamid whose fossils were found in the Charnwood Forest of Leicestershire, England. It serves as an important rangeomorph because of its multifoliate anatomy. Its overall body plan is similar to that of a goblet, from which its name, Hylaecullulus, is derived from.

References

  1. 1 2 3 Narbonne, G. M. (August 2004). "Modular Construction of Early Ediacaran Complex Life Forms". Science. 305 (5687): 1141–1144. Bibcode:2004Sci...305.1141N. doi: 10.1126/science.1099727 . ISSN   0036-8075. PMID   15256615. S2CID   44647427.
  2. ↑ Hoyal Cuthill, JF; Conway Morris, S (2014). "Fractal branching organizations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan". Proceedings of the National Academy of Sciences. 111 (36): 13122–13126. Bibcode:2014PNAS..11113122H. doi: 10.1073/pnas.1408542111 . PMC   4246981 . PMID   25114255.
  3. ↑ Laflamme, M.; Xiao, S.; Kowalewski, M. (2009). "Osmotrophy in modular Ediacara organisms". Proceedings of the National Academy of Sciences. 106 (34): 14438–14443. Bibcode:2009PNAS..10614438L. doi: 10.1073/pnas.0904836106 . PMC   2732876 . PMID   19706530.
  4. ↑ Droser, ML; Gehling, JG (2015). "The advent of animals: The view from the Ediacaran". Proceedings of the National Academy of Sciences. 112 (16): 4865–4870. Bibcode:2015PNAS..112.4865D. doi: 10.1073/pnas.1403669112 . PMC   4413262 . PMID   25901306.
  5. ↑ Liu, Alexander G; Kenchington, Charlotte G; Mitchell, Emily G (2015). "Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota". Gondwana Research. 27 (4): 1355–1380. Bibcode:2015GondR..27.1355L. doi: 10.1016/j.gr.2014.11.002 . hdl: 1983/ef181134-4023-4747-8137-ed9da7a97771 .
  6. 1 2 Antcliffe, Jonathan B.; Brasier, Martin D. (January 2008). "Charnia at 50: Developmental Models for Ediacaran Fronds". Palaeontology. 51 (1): 11–26. doi:10.1111/j.1475-4983.2007.00738.x. ISSN   0031-0239.
  7. 1 2 3 Xiao, S.; Laflamme, M. (January 2009). "On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota". Trends in Ecology and Evolution . 24 (1): 31–40. doi:10.1016/j.tree.2008.07.015. PMID   18952316.
  8. ↑ Mitchell, Emily G.; Kenchington, Charlotte G.; Liu, Alexander G.; Matthews, Jack J.; Butterfield, Nicholas J. (2015). "Reconstructing the reproductive mode of an Ediacaran macro-organism" (PDF). Nature. 524 (7565): 343–346. Bibcode:2015Natur.524..343M. doi:10.1038/nature14646. hdl: 1983/93446a6e-8c30-4927-992b-1f7fea755961 . PMID   26237408. S2CID   4471588.
  9. ↑ Collins, Sarah (3 August 2015). "Earliest evidence of reproduction in a complex organism". University of Cambridge. Retrieved 3 August 2015.
  10. ↑ Liu, Alexander G.; Dunn, Frances S. (April 2020). "Filamentous Connections between Ediacaran Fronds". Current Biology. 30 (7): 1322–1328.e3. doi:10.1016/j.cub.2020.01.052. ISSN   0960-9822.
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