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The Ediacaran Period is a geological period that spans 94 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 541 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.
The Neoproterozoic Era is the unit of geologic time from 1,000 million to 541 million years ago.
The cloudinids, an early metazoan family containing the genera Acuticocloudina, Cloudina and Conotubus, lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed millimetre-scale conical fossils consisting of calcareous cones nested within one another; the appearance of the organism itself remains unknown. The name Cloudina honors the 20th-century geologist and paleontologist Preston Cloud.
The Polychaeta, also known as the bristle worms or polychaetes, are a paraphyletic class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common representatives include the lugworm and the sandworm or clam worm Alitta.
A scolecodont is the jaw of a polychaete annelid, a common type of fossil-producing segmented worm useful in invertebrate paleontology. Scolecodonts are common and diverse microfossils, which range from the Cambrian period to the present. They diversified profusely in the Ordovician, and are most common in the Ordovician, Silurian and Devonian marine deposits of the Paleozoic era.
Spriggina is a genus of early bilaterian 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. The organism reached about 3–5 centimetres (1.2–2.0 in) in length and may have been predatory. Its bottom was covered with two rows of tough interlocking plates, while one row covered its top; its front few segments fused to form a "head."
A body plan, Bauplan, or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrate body plan is one of many: invertebrates consist of many phyla.
Marywadea is a genus of Ediacaran biota shaped like an oval with a central ridge. It is a bilaterian organism as evidenced by its symmetry, vaguely resembling a very primitive trilobite. The fossil has an asymmetrical first chamber of the quilt. It has transverse ridges away from the central axis that may be gonads. The head is shaped as a semicircle and is the same width as the rest of the body. The ridges number about 50. There are two oval shapes below the head.
Odontogriphus is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as 12.5 centimetres (4.9 in) in length, Odontogriphus is a flat, oval bilaterian which apparently had a single muscular foot, and a "shell" on its back that was moderately rigid but of a material unsuited to fossilization.
The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were composed of 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.
Proarticulata is a proposed phylum of extinct, bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately 567 to 550 million years ago. The name comes from the Greek προ = "before" and Articulata, i.e. prior to animals with true segmentation such as annelids and arthropods. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as Dickinsonia, Vendia, Cephalonega, Praecambridium and currently many other Proarticulata are described.
Evidence suggesting that a mass extinction occurred at the end of the Ediacaran period, 542 million years ago, includes:
Protostomia is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia. Some examples of protostomes are arthropods, molluscs, and tardigrades.
The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa. The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most members of the Lophotrochozoa.
Yelovichnus is an "enigmatic" genus known from fossils of the Ediacaran period. Yelovichnus was originally believed to be an ichnotaxon: its fossils, because of their "meandering nature", were initially thought to be feeding trails left by other life forms, such as annelids or mollusks. Better-preserved specimens later demonstrated that the fossils were not true feeding trails, as there was no evidence of turning by the life form that supposedly left them. The fossils are now recognized as belonging to an organism taking the form of "collapsed, segmented tubes", possibly an alga or a protist. It has also been argued that Yelovichnus and similar organisms are xenophyophores, large but single-cellular organisms that exist today in the abyssal zone. Due to similar structures found in their fossils, it is theorized that Yelovichnus may be related to Palaeopascichnus, as well as Aspidella and Neonereites. The main difference between Yelovichnus and Palaeopasicichnus is the shape of their segments: the segments of Yelovichnus took the shape of "closed, ovate-shaped loops", whereas the segments of Palaeopascichnus were quite varied in shape.
The annelids, also known as the ringed worms or segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
Sekwitubulus annulatus is an Ediacaran tubular fossil from the Blueflower Formation in Canada. Sekwitubulus is a monotypic genus, containing only the single species. S. annulatus is possibly a type of annelid worm. The name derives from the area the type specimen was found, Sekwi.
Protonympha is a form genus for problematic fossils of Devonian age in New York. It has been of special interest because of its morphological similarity with the iconic Ediacaran fossil Spriggina, and may have been a late surviving vendobiont.
Yilingia spiciformis was a worm-like animal that lived approximately between 551 million and 539 million years ago in the Ediacaran period, around 10 million years before the Cambrian explosion. A fossil of this creature and its tracks were discovered in 2019 in Southern China. It was a segmented bilaterian, conceivably related to panarthropods or annelids. It is a rare example of a complex Ediacaran animal that is similar to animals that existed since the Cambrian, hence suggesting that perhaps the Cambrian explosion was less sudden than often assumed.
The following are lists of prehistoric animals:
References
- ↑ YANISHEVSKY, M (1926). "On the remains of the tubular worms from the Cambrian blue clays". Ezhegodnik Russkogo Paleontologicheskogo Obchestva. 4: 99–112.
- 1 2 "Microstructure and Biogeochemistry of the Organically Preserved Ediacaran Metazoan Sabellidites". BioOne. doi:10.1666/13-003 . Retrieved 2017-12-08.
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