''Ernietta'' is an extinct genus of Ediacaran organisms with an infaunal lifestyle. Fossil preservations and modeling indicate this organism was sessile and “sack”-shaped. It survived partly buried in substrate, with an upturned bell-shaped frill exposed above the sediment-water interface. ''Ernietta'' have been recovered from present-day Namibia, and are a part of the Ediacaran biota, a late Proterozoic radiation of multicellular organisms. They are among the earliest complex multicellular organisms and are known from the late Ediacaran (ca. 548 Ma to 541 Ma). ''Ernietta plateauensis'' remains the sole species of the genus.

Biology and paleoecology

Fossil specimens show individuals to have lived partly buried in the substrate, as well as filled to some degree by substrate material. An exposed frill extended out of the substrate and was thought to have conducted feeding in the water column. Modeling based on fossil specimens show that the frill possessed an “upturned bell” shape. Water and nutrients circulated within this bell cavity, and the organism is thought to have engaged in suspension feeding. It is possible that appendages which carried out feeding were not preserved in fossils. Previously, ''Ernietta'' were thought to have obtained nutrients by passive absorption, however, this is currently unsupported given the high volume to surface area ratio observed in ''Ernietta''''.'' Alternatively ''Ernietta'' may have lived from associated symbiotic algae. Hydrodynamic modeling carried out by Gibson et al. in 2019 assumed that ''Ernietta'' inhabited shallow marine environments in aggregations. Nutrient delivery was found to be optimized when individuals were situated in “clumped” formations, with multiple individuals aggregated in groups located upstream or downstream from one another. This formation enhanced both vertical mixing and the direction of nutrient-rich currents to the bodies of downstream individuals. This may thus be one of the earliest examples of

commensalism Commensalism is a long-term biological interaction ( symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fr ...

, in which organisms act to mutual benefit. Ernietta plateauensis 1

The body of ''Ernietta'' is composed of a layer of tubes (with some preservations indicating a double-layer of tubes). Perpendicular to these tubes is an equatorial seam. The body is asymmetrical along either side of this seam. The presence of this seam and offset symmetry unites the Ernettiomorpha, which includes taxa more similar to ''Ernietta'' (for example, ''

Pteridinium ''Pteridinium'' is an erniettomorph found in a number of Precambrian deposits worldwide. It is a member of the Ediacaran biota. Body plan The three-lobed body is generally flat such that only two lobes are visible. Each lobe consists of a number ...

Swartpuntia ''Swartpuntia'' is a monospecific genus of erniettomorph from the terminal Ediacaran period, with at least three quilted, leaf-shaped petaloids — probably five or six. The petaloids comprise vertical sheets of tubes filled with sand. ''Swartp ...

,'' and ''Mietta'') than to the rangeomorphs. ''Ernietta'' has been considered a benthic shallow marine fossil comparable with an anemone. However

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 ...

, researcher who supports theory that Ediacaran biota like '' Dickinsonia'' being lichens, claimed that there is evidence for freshwater environments from its low boron content compared with other Ediacaran fossils. His study also shows that specimens have been found covered with thin layers of wind-drift sand of alluvial levees.

Biogeography

All occurrences of ''Ernietta'' are known from the

Nama Group The Nama Group is a megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two e ...

(specifically, the Kuibis and Schwarzrand subgroups) of present-day

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

. The Nama Group consists of fluvial and shallow marine sediments that span the Ediacaran to the Cambrian (approximately spanning from 570 to 543 Ma). Formations of the Nama Group outcrop across southern Namibia. Most specimens of ''Ernietta'' are preserved in

sandstones Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) b ...

, with a single occurrence in a siltstone. Fossils of the Aar Member of the Nama Group in particular are preserved within beds of cross-stratified sandstones. A significant discovery of this taxon was reported in 2016, at the Farm Aar field site in southern Namibia, which recovered a number of specimens preserved in life position in the water column. This

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

of this site has been interpreted as subtidal, with periodic influxes of storm-induced sands. Other reports of ''Ernietta'' exist outside Namibia, including Nevada, USA An occurrence in the Windermere group of British Columbia, Canada has not yet been described.

Taxonomy, history and preservational forms

Ediacaran fossils are difficult to assign to taxonomic classifications based on modern organisms, as they have no living representatives. ''Ernietta'' is the type genus for the clade Ernettiomorpha. As a whole, the Ediacaran biota have been variously defined as early marine animals, cnidarians, lichens, bacterial colonies, or an intermediate between plants and animals. The ''Ernietta'' genus contains a sole species: ''Ernietta plateauensis''. This species is the type species of the Ernettiomorpha and was first described in 1966 by Pflug. In 1972, Pflug described a large number of new fossils which he placed into 13 genera and 29 species, all of which were later synonymized and united in a single species, ''Ernietta plateauensis''. These synonymized taxa include: *''Ernietta tschanabis'' Phlug, 1972 ::''E. aarensis'' Phlug, 1972 *''Erniaster aportus'' Phlug, 1972 ::''E. patellus'' Phlug, 1972 *''Erniobaris baroides'' Phlug, 1972 ::''E. epistuta'' Phlug, 1972 ::''E. gula'' Phlug, 1972 ::''E. parietalis'' Phlug, 1972 *''Erniobeta forensis'' Phlug, 1972 ::''E. scapulosa'' Phlug, 1972 *''Erniocarpis sermo'' Phlug, 1972 *''Erntocentris centriformis'' Phlug, 1972 *''Erniodiscus clypeus'' Phlug, 1972 ::''E. rutilus'' Phlug, 1972 *''Erniofossa prognatha'' Phlug, 1972 *''Erniograndis paraglossa'' Phlug, 1972 ::''E. sandalix'' Phlug, 1972 *''Ernionorma abyssoides'' Phlug, 1972 ::''E. clausula'' Phlug, 1972 ::''E. peltis'' Phlug, 1972 ::''E. rector'' Phlug, 1972 ::''E. tribunalis'' Phlug, 1972 *''Erniopelta scruputa'' Phlug, 1972 *''Erniotaxls segmontrix'' Phlug, 1972

Biology and paleoecology

Biogeography

Taxonomy, history and preservational forms

See also

References

Further reading