Tribrachidium
Encyclopedia
Tribrachidium heraldicum ("Heraldic Three Arms") was an early Ediacaran
organism famous for its unusual tri-radial symmetry. It was named and first described from South Australia
by Martin Glaessner
and Brian Daily in 1959.
Tribrachidium fossils are found in Ediacaran-type localities of the Ediacara Hills
, Australia
, in siliciclastic sediments of the White Sea
, Russia
, and Podolia
, Ukraine
. These fossils demonstrate a disc-shaped creature about 5 cm in diameter on average, with three curved "arms" extending from the center to nearly the edge. These arms were probably hollow and could be inflated or deflated. This threefold symmetry is almost unique in animals, which are usually either bilaterally or radially symmetric. Fleshy ridges, or possibly loose filaments, extended from the edges of the arms and formed the rest of the body.
Like many Precambrian
fossils, the relationship of Tribrachidium to other animals is poorly known. To some extent, it has become a poster child
for the problem in general, often being shown as an example of that era's peculiar lifeforms. Among others, Tribrachidium has been described variously as a cnidaria
n, lophophore
, echinoderm
, ecdysozoa
n, or a sponge.
Tribrachidium is closely related to Albumares brunsae
and Anfesta stankovskii
from Ediacaran (Vendian) rocks of the White Sea. These three, together with various other triradially symmetrical Ediacaran and Early Cambrian
organisms (including Rugoconites
, Ventogyrus, Vendoconularia
, Anabarites
and others) form the extinct Phylum
Trilobozoa
(though some authorities treat Trilobozoa as a class
within Cnidaria
).
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
organism famous for its unusual tri-radial symmetry. It was named and first described from South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
by Martin Glaessner
Martin Glaessner
Martin Fritz Glaessner AM was a geologist and palaeontologist. Born and educated in Austro-Hungarian Empire, he spent the majority of his life in working for oil companies in Russia, and studying the geology of the South Pacific in Australia...
and Brian Daily in 1959.
Tribrachidium fossils are found in Ediacaran-type localities of the Ediacara Hills
Ediacara Hills
Ediacara Hills are a range of low hills in the northern part of the Flinders Ranges of South Australia, around 650 km north of Adelaide. The area has many old copper and silver mines from mining activity in the late 19th century...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, in siliciclastic sediments of the White Sea
White Sea
The White Sea is a southern inlet of the Barents Sea located on the northwest coast of Russia. It is surrounded by Karelia to the west, the Kola Peninsula to the north, and the Kanin Peninsula to the northeast. The whole of the White Sea is under Russian sovereignty and considered to be part of...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
, and Podolia
Podolia
The region of Podolia is an historical region in the west-central and south-west portions of present-day Ukraine, corresponding to Khmelnytskyi Oblast and Vinnytsia Oblast. Northern Transnistria, in Moldova, is also a part of Podolia...
, Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...
. These fossils demonstrate a disc-shaped creature about 5 cm in diameter on average, with three curved "arms" extending from the center to nearly the edge. These arms were probably hollow and could be inflated or deflated. This threefold symmetry is almost unique in animals, which are usually either bilaterally or radially symmetric. Fleshy ridges, or possibly loose filaments, extended from the edges of the arms and formed the rest of the body.
Like many Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
fossils, the relationship of Tribrachidium to other animals is poorly known. To some extent, it has become a poster child
Poster child
A poster child is a child afflicted by some disease or deformity whose picture is used on posters or other media as part of a campaign to raise money or enlist volunteers for a cause or organization...
for the problem in general, often being shown as an example of that era's peculiar lifeforms. Among others, Tribrachidium has been described variously as a cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
n, lophophore
Lophophore
The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Entoprocta, and Phoronida. All lophophores are found in aquatic organisms.-Characteristics:...
, echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
, ecdysozoa
Ecdysozoa
Ecdysozoa is a group of protostome animals, including Arthropoda , Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes...
n, or a sponge.
Tribrachidium is closely related to Albumares brunsae
Albumares brunsae
Albumares brunsae was a trilobozoan closely related to Tribrachidium heraldicum. It was up to 15 mm in diameter, and unlike the related circular Anfesta stankovskii was divided into three lobes that gave it a trefoil-like appearance. Its fossils have been found in Ediacaran beds on the Syuzma...
and Anfesta stankovskii
Anfesta stankovskii
Anfesta stankovskii was a trilobozoan closely related to Tribrachidium heraldicum. It was 18 mm in diameter, and, like Albumares, was divided into three lobes, but Anfesta was circular in appearance, as opposed to its trefoil-shaped relative. Its fossils have been found in Ediacaran beds of the...
from Ediacaran (Vendian) rocks of the White Sea. These three, together with various other triradially symmetrical Ediacaran and Early Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
organisms (including Rugoconites
Rugoconites
A member of the Ediacaran biota which takes the form of a circular to oval impression preserved in hyporelief, six or more centimeters in diameter. They are surrounded by a frill that has been interpreted as a set of tentacles...
, Ventogyrus, Vendoconularia
Vendoconularia
Vendoconularia is a genus of Ediacaran organism consisting of a hexagonal cone, which is thought to have housed a tentaculate organism. Three longitudinal bands are interspersed between the six sides of the cone. The discovery of vendoconulariids in Proterozoic strata of Russia confirmed a 1987...
, Anabarites
Anabarites
Anabarites is a problematic lower Cambrian genus, and is one of the small shelly fossils. It was abundant in the early Tommotian and is also found in the Nemakit-Daldynian....
and others) form the extinct Phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Trilobozoa
Trilobozoa
Trilobozoa is an extinct taxon of organisms which displayed tri-radial symmetry. Trilobozoans were most dominant during the Ediacaran period — prior to the Cambrian explosion of modern life forms....
(though some authorities treat Trilobozoa as a class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
within Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
).
External links
- Palaeos dendrogram
- Ediacara Assemblage University of Bristol
- Anatomical Information Content in the Ediacaran Fossils and Their Possible Zoological Affinities, Jerry Dzik, Instytut Paleobiologii PAN, Twarda 51/55, 00-818 Warszawa, Poland