| Tribrachidium heraldicum Temporal range: 560–555 Ma Ediacaran - 560–555 Ma[1] |
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| Fossil of Tribrachidium heraldicum | |
| reconstruction | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Trilobozoa |
| Family: | Tribrachididae |
| Genus: | Tribrachidium Glaessner, 1959 |
| Species: | T. heraldicum |
| Binomial name | |
| Tribrachidium heraldicum Glaessner, 1959 |
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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.[2]
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 cnidarian, lophophore, echinoderm, ecdysozoan, or a sponge.
Tribrachidium is closely related to Albumares brunsae and Anfesta stankovskii[3][4] 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[5]) form the extinct Phylum Trilobozoa[6] (though some authorities treat Trilobozoa as a class within Cnidaria[3]).
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