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.
Bilateria is a large clade or infrakingdom of animals called bilaterians, characterized by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front and a rear end, as well as a left–right–symmetrical belly (ventral) and back (dorsal) surface. Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms, which extend to pentaradial symmetry as adults, but are only bilaterally symmetrical as an embryo. Cephalization is also a characteristic feature among most bilaterians, where the special sense organs and central nerve ganglia become concentrated at the front/rostral end.
Ecdysozoa is a group of protostome animals, including Arthropoda, Nematoda, and several smaller phyla. The grouping of these animal phyla into a single clade was first proposed by Eernisse et al. (1992) based on a phylogenetic analysis of 141 morphological characters of ultrastructural and embryological phenotypes. This clade, that is, a group consisting of a common ancestor and all its descendants, was formally named by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.
Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. It lived during the late Ediacaran. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.
Kimberella is an extinct genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods, although its affinity with this group is contentious.
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.
Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.
Parvancorina is a genus of shield-shaped bilaterally symmetrical fossil animal that lived in the late Ediacaran seafloor. It has some superficial similarities with the Cambrian trilobite-like arthropods.
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 "Cambrian substrate revolution" or "Agronomic revolution", evidenced in trace fossils, is a sudden diversification of animal burrowing during the early Cambrian period.
The Cambrian explosion is an interval of time beginning approximately 538.8 million years ago in the Cambrian period of the early Paleozoic, when a sudden radiation of complex life occurred and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.
The urbilaterian is the hypothetical last common ancestor of the bilaterian clade, i.e., all animals having a bilateral symmetry.
Nematoida is a clade of pseudocoelomate free living or parasitic animals. It consists of phyla Nematoda and Nematomorpha. The two groups share a number of features in common; the presence of a cloaca in both sexes, aflagellate sperm, and a cuticle made of collagen.
The Avalon explosion, named from the Precambrian faunal trace fossils discovered on the Avalon Peninsula in Newfoundland, eastern Canada, is a proposed evolutionary radiation of prehistoric animals about 575 million years ago in the Ediacaran period, with the Avalon explosion being one of three eras grouped in this time period. This evolutionary event is believed to have occurred some 33 million years earlier than the Cambrian explosion, which had been long thought to be when complex life started on Earth.
Kimberichnus is an ichnofossil associated with the early bilaterian Kimberella. It is known mostly from shallow marine Ediacaran sediments, often occurring alongside its producer. Kimberichnus often occurs in Russia and South Australia, where it is most abundant in the shape of multiple arcuate sets of ridges with fan-shaped arrangements.
Nilpena Ediacara National Park, which includes the former Ediacara Conservation Park, is a protected area located in the northern Flinders Ranges, in the state of South Australia. It is located about around 551 km (342 mi) north of the city of Adelaide, around 30 kilometres south-west of the town of Leigh Creek in the state's Far North.
The Ediacaran fossil Hallidaya, a close relative of Skinnera lived in Belomorian of the Late Ediacaran period prior to the Cambrian explosion and thrived in the marine strata on the ocean floor of what is now considered Australia. These fossils were disk-shaped organisms that were slightly dome shaped with tri-radial symmetry. These Ediacaran organisms thrived by living in low-energy inner shelf, in the wave- and current-agitated shoreface, and in the high-energy distributary systems.
Ikaria wariootia is an early example of a wormlike, 2–7 mm-long (0.1–0.3 in) bilaterian organism. Its fossils are found in rocks of the Ediacara Member of South Australia that are estimated to be between 560 and 555 million years old. A representative of the Ediacaran biota, Ikaria lived during the Ediacaran period, roughly 15 million years before the Cambrian, when the Cambrian explosion occurred and where widespread fossil evidence of modern bilaterian taxa appear in the fossil record.
Attenborites janeae is a species of Ediacaran organism from South Australia first described by a team led by Palaeontologist Mary L. Droser in 2018. The genus Attenborites was named after Sir David Attenborough. The bed in which the first 52 specimens from Australia of A. janeae was given the ARB designation "Alice's Restaurant Bed", and has been given that nickname for its abundance of rare taxa and newly described ones and is also a reference to Arlo Guthrie's 1967 song, "Alice's Restaurant". The new taxon is unique from all of these other taxa in the way that it has a much more irregular morphology than the other 52 specimens.
