Trilobozoa Temporal range: Late Ediacaran, around | |
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The many members of the Trilobozoa. (clockwise from top): Tribrachidium, Rugoconites enigmaticus, R. tenuirugosusAlbumares brunsae, Hallidaya brueri, Anfesta stankovskii, Lorenzinites rarus, Wigwamiella enigmatica and Skinerra brooksi. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Subkingdom: | Eumetazoa |
Phylum: | † Trilobozoa Fedonkin, 1985 [nom. transl. Runnegar, 1992 ex Class Trilobozoa Fedonkin, 1985] |
Genera | |
For minor descriptions, see text | |
Synonyms | |
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Trilobozoa (meaning "three-lobed animals") is a phylum of extinct, sessile animals that were originally classified into the Cnidaria. The basic body plan of trilobozoans is often a triradial or radial sphere-shaped form with lobes radiating from its centre. [1] Fossils of trilobozoans are restricted to marine strata of the Late Ediacaran period.
Originally, both M.A. Fedonkin and B.N. Runnegar presumed that there were 2–3 families within the Trilobozoa, those families being Albumaresidae (Fedonkin, 1985) and Tribrachididae (Runnegar, 1992). [2] Although, affinities with the Conulariida were made because the conulariids possess similar three-fold symmetry. [3] Fedonkin later classified the Trilobozoa as a class of the phylum Coelenterata.[ citation needed ]
Most of the members of what is now the modern day classification for Trilobozoa were thought to have originally been free swimming Jellyfish. [4] Tribrachidium was once interpreted as a Edrioasteroid Echinoderm, although with the discovery of the related Albumares and Anfesta (along with better-preserved White Sea specimens), it became apparent to M. Fedonkin that all of the organisms formed one phylum (originally class) of triradially symmetrical enigmatic organisms from the Ediacaran. [1] The eventual split of Coelenterata into the phyla Cnidaria and Ctenophora led the Trilobozoa to obtain a phylum level of affinities. [5]
The members of the Trilobozoa are now thought to be sessile, benthic organisms of unknown affinities, and are a subject open for interpretations and debate.
Trilobozoans had a triradial shield-like body that had three antimeres which consisted of a cluster of grooves on their outer surface and within their inner cavity. [1] Most of the members of the Trilobozoa possessed bifurcating concave areas internally that were all separated by sharp ridges. [6] These structures were more likely stiff and culticular rather than elastic internal bodies or membranes [6] even though those structures may have been resistant, they also could've corresponded to collapsed chambers that can be observed within the related genera Albumares and Anfesta. In Tribrachidium , the sediment preserving the animal penetrated from above only within areas between those organs. The spiral-like orientation of the internal bodies of trilobozoans suggests that they were modified from an originally longitudinal to the axis which resulted in the deposition of the organs. [6]
Albumares brunsae represents a form first described from the White Sea of Russia by Mikhail A. Fedonkin in 1976. [2] In life, Albumares most likely had an umbrella-like shape with triradial symmetry along with three ridges radiating from its centre. Fossils of Albumares are known from Russia and South Australia and preserve 100 small (0.15 millimeters (0.0059 in) each) marginal tentacles. From the centre of the lobes arise three canals that split at least 4 times across the body. [2] The split canals then split until they reach the outer margin of the body. The diameter of the body is 13 millimeters (0.51 in), the length of the lobes are 5 millimeters (0.20 in) maximum. [2] Albumares are similar and may be a close relative of Anfesta.
Anfesta stankovskii represents a small (18 millimeters (0.71 in)) hemispherical-shaped form with flattened, three-fold symmetry. [2] Similarly to Albumares, three long sausage-shaped lobes radiate from its centre that are all separated by an angle of about 120 degrees. The lobes taper at both their proximal and distal ends, which divide the organism into a number of narrow bodies that are divisible by three. Some specimens from both Australia and Russia preserve tentacles (canals) similar to that of Albumares. [2] Unlike Albumares and Skinnera , Anfesta is more oval-shaped and discoidal rather than being dominantly tri-lobate. The length of the lobes are 5 millimeters (0.20 in) with the width reaching up to 1.3 millimeters (0.051 in). [2]
Hallidaya brueri constitutes as a discoidal form that is restricted to Mount Skinner of the Northern Territory of Australia. [7] The fossils were preserved as disc-shaped moulds on the sandstone. The fossils typically range up to 4 to 32 mm (0.16 to 1.26 in) in diameter with a height of 2 mm (0.079 in). Specimens commonly show three central depressions connected by a much smaller, pouch-shaped one around the perimeter of the disk by multiple canals radiating from its centre. [7] Hallidaya and Skinnera share common morphological characteristics with each other and are most likely close relatives. [7]
Rugoconites is a genus of oval-circular-shaped preserved in high relief about 6 centimetres (2.4 in) or more in diameter. The shape of Rugoconites is different in both of its species; R. enigmaticus(Glaessner & Wade, 1966) is more dome shaped and R. tenuirugosus(Wade, 1972) is flatter although bigger. [8] Wade (1972) interpreted the multiple lobes of Rugoconites as being tentacles. The multiple bifurcating lobes radiating from a centre served to distinguish Rugoconites from the sponge Palaeophragmodictya the lobes were then reinterpreted as being traces of a Gastrovascular system. [9] However this idea was countered by Sepkoski (2002) who went on to actually classify the genus into the Cnidaria instead of the Porifera. [10] Ivantstov & Fedonkin (2002) went on to classify Rugoconites into the Trilobozoa by suggesting it had triradial symmetry. [3]
Skinnera brooksi defines small discoidal fossils preserved as composite moulds on sandstone. [7] Fossils are characterized by three radially arranged pouch-shaped depressions that are interpreted as a stomach similar to that seen in Hallidaya. These depressions are then connected to an outer rim by approximately 15 smaller pouches along the disk by canals. [7] S. brooksi fossils range from 3.9 millimeters (0.15 in) to 32 millimeters (1.3 in) and are slightly domed by being 2 millimeters (0.079 in) tall. Skinnera and Hallidaya are considered to be close relatives. [7]
Tribrachidium heraldicum is a small 3 to 40 millimetres (0.12 to 1.57 in) [11] triradially symmetrical form often preserved on the base of sandstones and often show a three-lobed, circular animal preserved in it. [12] The central part of T. heraldicum has three hooked ridges (or arms) that make up the lobes; the arms are covered by numerous branched furrows that were interpreted as tentacles. [12] [13]
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.
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.
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.
Cephalonega stepanovi is a fossil organism from Ediacaran deposits of the Arkhangelsk Region, Russia. It was described by Mikhail A. Fedonkin in 1976
Hiemalora is a fossil of the Ediacaran biota, reaching around 3 cm in diameter, which superficially resembles a sea anemone. The genus has a sack-like body with faint radiating lines originally interpreted as tentacles, but discovery of a frond-like structure seemingly attached to some Heimalora has added weight to a competing interpretation: that it represents the holdfast of a larger organism.
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.
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.
Anfesta stankovskii is a tri-radially symmetrical fossil animal that lived in the late Ediacaran (Vendian) seafloor. It is a member of the extinct group Trilobozoa.
Proarticulata is a proposed phylum of extinct, near-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.
Protechiurus edmondsi is a species of fossil animal from the Ediacaran Nama group of Namibia. It was initially interpreted as an echiurid worm. It has been placed as a "vendobiont", on the hypothesis that the Edicarian fauna represent a distinct phylum. It has also been suggested that it may be an ecdysozoan.
Ventogyrus is an Ediacaran fossil found in the White Sea-Arkhangelsk region of Russia. It was first discovered in the Teska member of the Ust'-Pinega formation, in a thick lens of sandstone, originally sand dumped by storm waves that cut a deep channel through the shallow sea bottom where the organisms lived. Many individuals were preserved on top of each other, often torn or in distorted positions. As a result, it was originally thought to have had a "boat shaped" form and to have lived anchored in the sea floor. However, a nearby site discovered later by Mikhail Fedonkin yielded separate specimens which were beautifully preserved in an upright position and showed the internal anatomy.
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.
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.
Persimedusites chahgazensis is a Precambrian discoidal species which are believed to have existed primarily during the late Ediacaran period. It was discovered initially in the Kushk Series in the Bafq and Behabad regions of central Iran, along with similarly aged specimen of Cloudina and Corumbella. The body fossils of these disc-shaped organisms are approximately one centimeter in diameter, and were noted to have symmetrical internal lobes, as well as secondary distal branches.
Eoporpita is a disc or ellipse-shaped Ediacaran fossil with unsure taxonomy/classification. It is known from its type species, Eoporpitamedusa, the only species within the genus Eoporpita.
Gehlingia dibrachida is a species of enigmatic Ediacaran organism from South Australia described in 1998. Gehlingia has been described as having many characteristics of petalonamids, although it has been classified as a rather close relative of the Tribrachidium. The overall shape of Gehlingia contradicts this affinity, however, with its shape being a more Bilaterally symmetrical one although the basic structure similar to that of Tribrachidium appears in Gehlingia as separate branches extending into bifurcating minor branches along with "thumb structures" that are apparent in Tribrachidium in the form of side bulges on an axis.