| Parvancorina Temporal range: Ediacaran, around | |
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| Schematic reconstructions of P. sagitta and P. minchami | |
| Scientific classification | |
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| Genus: | †Parvancorina Glaessner 1958 |
| Type species | |
| P. minchami Glaessner 1958 | |
| Species | |
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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 generic name is derived from a crasis compound word from the Latin parva ancora (small anchor).
The specific name of the type species, P. minchami, honors Mr. H. Mincham, the private collector, who in 1957 had collected and presented a number of fine specimens of Ediacaran fossils to the South Australian Museum.
The specific name of P. sagitta is the Latin word sagitta (arrow), in direct reference to the arrow-like shape.
P. minchami fossils were first discovered in the Ediacara Member of the Rawnslay Quartzite, Flinders Ranges, in South Australia. [1] This species is also known from deposits of the Verkhovka, Zimnegory and Yorga Formations in the White Sea area of the Arkhangelsk Region, Russia. Additionally, similar poorly preserved Parvancorina sp. fossils were found in the Lyamtsa Formation of this Russian region. [2]
P. sagitta is found in the Verkhovka formation on the Solza River, White Sea area of the Arkhangelsk Region, Russia. [3]
It has a raised ridge down the central axis of symmetry. This ridge can be high in unflattened fossils. At the 'head' end of the ridge there are two quarter-circle-shaped raised arcs attached. In front of this are two nested semicircular lines. Teeth seem to come from the raised parts pointing into the centre spaces.[ citation needed ] These may show as raised lines.
The fossils are normally about 1 centimetre (0.39 inches) in each of width and length, but can be up to 2 centimetres (0.79 inches).
In attempting to determine its phylogenic relationships, Parvancorina has been compared with trilobite-like arthropods, such as Skania from the Burgess Shale Biota, Canada, and Primicaris from the Chengjiang Biota, China. [4] [5] However, the growth form of Parvancorina is unusual for an arthropod. [2] Furthermore, the strong resemblance of P. sagitta to the primitive mollusk-like bilateran Temnoxa [3] and similarities to parts of Kimberella [6] casts further doubt on an arthropod affinity.
Parvancorina typically lived with their "heads" parallel to the current direction. [7] Overfolding of the fossils from all sides contradicts any form of stalked attachment to the sea floor. [8] They are suggested to have been mobile and able to actively orientate their bodies towards the current direction, with smaller individuals from the Ediacara biota in Australia often found in close association with each other. [9] They have been proposed to be filter feeders, using their body ridges to direct water towards feeding structures, with deposit feeding being a possible but less likely ecology. [7]
Dickinsonia is a genus of extinct organism that lived during the late Ediacaran period in what is now Australia, China, Russia and Ukraine, most likely a basal animal. 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. 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.
Tribrachidium heraldicum is a tri-radially symmetric fossil animal that lived in the late Ediacaran (Vendian) seas. In life, it was hemispherical in form. T. heraldicum is the best known member of the extinct group Trilobozoa.
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.
Yorgia waggoneri is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of 25 cm (9.8 in). It is classified within the extinct animal phylum Proarticulata.
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.
Cephalonega stepanovi is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976
Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.
Trilobozoa is a phylum of extinct, sessile animals that were originally classified into the Cnidaria. The basic body plan of trilobozoans is often a tri-radial or radial sphere-shaped form with lobes radiating from its centre. Fossils of trilobozoans are restricted to marine strata of the Late Ediacaran period.
Praecambridium sigillum is an extinct organism that superficially resembles a segmented trilobite-like arthropod. It was originally described as being a trilobite-like arthropod, though the majority of experts now place it within the Proarticulata as a close relative of the much larger Yorgia. It is from the Late Ediacaran deposit of Ediacara Hills, Australia, about 555 million years ago. On average, P. sigillum had at least 5 pairs of segments, with each unit becoming progressively larger as they approach the cephalon-like head.
Ovatoscutum concentricum is one of many enigmatic organisms known from the Ediacaran deposits of the Flinders Ranges, Australia, and the White Sea area in Russia, dating around 555 Ma.
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.
Albumares brunsae is a tri-radially symmetrical fossil animal that lived in the late Ediacaran seafloor. It is a member of the extinct group Trilobozoa.
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.
Rugoconites is a genus of Ediacaran biota found as fossils in the form of a circular or oval-like impression preserved in high relief, six or more centimeters in diameter. The fossils are surrounded by frills that have been interpreted as sets of tentacles. The bifurcating radial ribs, spreading from a central dome, serve to distinguish this genus from the sponge Palaeophragmodictya, and may represent the channels of the gastrovascular system. Fossils of Rugoconites have been interpreted as early sponges, although this is countered by Sepkoski et al. (2002), who interpreted the organism as a free-swimming jellyfish-like cnidarian; similar to Ovatoscutum. However, the fossil is consistently preserved as a neat circular form and its general morphology does not vary, therefore a benthic and perhaps slow-moving or sessile lifestyle is more likely. Ivantstov & Fedonkin (2002), suggest that Rugoconites may possess tri-radial symmetry and be a member of the Trilobozoa.
Vendiamorpha is a class of extinct animals within the Ediacaran phylum Proarticulata.
Palaeophragmodictya is an extinct genus of sponge-grade organisms from the Ediacaran Period. Originally interpreted as a hexactinellid sponge, the organism also bears some coelomate characteristics, including bilateral symmetry.
The petalonamids (Petalonamae) are an extinct group of archaic animals typical of the Ediacaran biota, also called frondomorphs, dating from approximately 635 million years ago to 516 million years ago. They are benthic and motionless animals, that have the shape of leaves, fronds (frondomorphic), feathers or spindles and were initially considered algae, octocorals or sea pens. It is now believed that there are no living descendants of the group, which shares a probable relation to the Ediacaran animals known as Vendozoans.
Cephalozoa are an extinct class of primitive segmented marine organisms within the Phylum Proarticulata from the Ediacaran period. They possessed bilateral symmetry and were characterized by a thin, rounded body.
