''Tribrachidium heraldicum'' is a tri-radially
symmetric
Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is invariant under some transformations ...
fossil animal that lived in the late
Ediacaran
The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
(Vendian) seas. In life, it was
hemispherical
A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
in form. ''T. heraldicum'' is the best known member of the extinct group
Trilobozoa
Trilobozoa, from Ancient Greek τρεῖς (''treîs''), meaning "three", λοβός (''lobós''), meaning "lobe", and ζῷον (''zôion''), meaning "animal", is a phylum of extinct, sessile animals that were originally classified into the Cnid ...
.
Etymology
The generic name ''Tribrachidium'' is derived from combination of the (, "three") + ("arm") + diminutive suffix . The specific name ''T. heraldicum'' references the similarity of the pattern of this fossil with the well-known heraldic
triskelion
A triskelion or triskeles is an ancient motif consisting either of a triple spiral exhibiting rotational symmetry or of other patterns in triplicate that emanate from a common center. The spiral design can be based on interlocking Archimedean s ...
design, such as the
coat of arms of the Isle of Man
The coat of arms of the Isle of Man, blazoned ''Gules three legs in armour flexed at the knee and conjoined at the thigh, all proper, garnished and spurred or'', dates from the late 13th century. The present version dates from 12 July 1996. As ...
.
Occurrence
''Tribrachidium'' fossils were first discovered in the Ediacara Member of the Rawnslay Quartzite,
Flinders Ranges
The Flinders Ranges are the largest mountain ranges in South Australia, which starts about north of Adelaide. The ranges stretch for over from Port Pirie to Lake Callabonna.
The Adnyamathanha people are the Aboriginal group who have inhab ...
in
South Australia
South Australia (commonly abbreviated as SA) is a States and territories of Australia, state in the southern central part of Australia. With a total land area of , it is the fourth-largest of Australia's states and territories by area, which in ...
.
This fossil is also known from the Mogilev Formation in the
Dniester River
The Dniester ( ) is a transboundary river in Eastern Europe. It runs first through Ukraine and then through Moldova (from which it more or less separates the breakaway territory of Transnistria), finally discharging into the Black Sea on Uk ...
Basin,
Podolia
Podolia or Podillia is a historic region in Eastern Europe located in the west-central and southwestern parts of Ukraine and northeastern Moldova (i.e. northern Transnistria).
Podolia is bordered by the Dniester River and Boh River. It features ...
,
Ukraine
Ukraine is a country in Eastern Europe. It is the List of European countries by area, second-largest country in Europe after Russia, which Russia–Ukraine border, borders it to the east and northeast. Ukraine also borders Belarus to the nor ...
and from the Verkhovka, Zimnegory and Yorga formations in the
White Sea
The White Sea (; Karelian language, Karelian and ; ) 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 nort ...
area of the
Arkhangelsk Region,
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
.
This fossil is also known from the Sonia Formation of Marwar Supergroup near
Jodhpur
Jodhpur () is the second-largest city of the north-western Indian state of Rajasthan, after its capital Jaipur. As of 2023, the city has a population of 1.83 million. It serves as the administrative headquarters of the Jodhpur district and ...
, India.
Description
''T. heraldicum'' is preserved as negative impressions on the base of sandstone beds. These fossils have a circular, three-lobe form, with straight or
trefoil
A trefoil () is a graphic form composed of the outline of three overlapping rings, used in architecture, Pagan and Christian symbolism, among other areas. The term is also applied to other symbols with a threefold shape. A similar shape with f ...
-like edges; they are usually covered by numerous radial branched furrows. The central part of the fossil has three hooked ridges ("arms"). The lobes are twisted into weak spirals.
The diameter of specimens ranges from . Its meter-scale distribution was found to be variable occurring both as solitary individuals and in groups.
Feeding Method
In a 2015 study, Rahman et al. proposed that ''Tribrachidium heraldicum'' used a rare 'gravity settling' mode of
suspension feeding
Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specia ...
based on computational fluid dynamics simulations, which showed that water flow was directed passively by the arms, funneling it towards three depressions (‘apical pits’) where water flow slowed down so that food particles would fall out of suspension.
Reconstruction and affinity
''Tribrachidium'' was originally described by
Martin Glaessner as a problematic organism, one that is excluded from all known major groups of animals by its tri-radial symmetry. However, ''Tribrachidiums superficial resemblance to
edrioasteroid echinoderms
An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larv ...
was well known to researchers and discussed.
Later, Glaessner rejected any putative affinities of this animal with any known phyla, leaving the status of its taxonomy uncertain.
Originally, the various structures on the poorly preserved Australian specimens were interpreted as tentacles, peculiar arms and mouth,
but later this interpretation was rejected. Its mode of locomotion in life also remains unknown.

With the discovery of the closely related ''
Albumares
''Albumares brunsae'' is a tri-radially symmetrical fossil animal that lived on the late Ediacaran seafloor. It is a member of the extinct group Trilobozoa.
Etymology
The generic name ''Albumares'' derives from the Latin ''Mare Album'' (White S ...
'' and ''
Anfesta
''Anfesta stankovskii'' is a tri-radially symmetrical fossil animal that lived on the late Ediacaran (Vendian) seafloor. It is a member of the extinct group Trilobozoa.
Etymology
The generic and specific names of ''Anfesta stankovskii'' honour ...
'', along with the discoveries of much better-preserved Russian specimens,
Mikhail Fedonkin
Academician Mikhail Aleksandrovich Fedonkin (; born June 19, 1946) is a Russian paleontologist specializing in documentation of the earliest animals' body fossils, tracks, and trails. He has also described numerous Vendian-aged fossils includin ...
proposed for these animals the new taxon,
Trilobozoa
Trilobozoa, from Ancient Greek τρεῖς (''treîs''), meaning "three", λοβός (''lobós''), meaning "lobe", and ζῷον (''zôion''), meaning "animal", is a phylum of extinct, sessile animals that were originally classified into the Cnid ...
– an extinct group of tri-radially symmetrical coelenterate-grade animals.
Originally, Trilobozoa was erected as a separate
class
Class, Classes, or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used d ...
in the phylum
Coelenterata
Coelenterata is a term encompassing the animal phyla Cnidaria (corals, true jellies, sea anemones, sea pens, and their relatives) and Ctenophora (comb jellies). The name comes , referring to the hollow body cavity common to these two phyla. Th ...
, but after Coelenterata was divided into separate phyla
Cnidaria
Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
and
Ctenophora
Ctenophora (; : ctenophore ) is a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and they are ...
, the Trilobozoa was transferred to the rank of
phylum
In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
.
M. Fedonkin has shown that the fossil of ''Tribrachidium'' is an imprint of the upper side of the animal's body, with some elements of its external and internal anatomy. The radial furrows on the fossil are radial grooves on the surface of the living animal, while the three hooked ridges in central part of the fossil are imprints of cavities within the body.
''Tribrachidium'' was a soft-bodied
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
organism that temporarily attached (but did not accrete) to the substrate of its habitat (
microbial mats
A microbial mat is a multi-layered sheet or biofilm of microbial colony (biology), colonies, composed of mainly bacteria and/or archaea. Microbial mats grow at interface (chemistry), interfaces between different types of material, mostly on submer ...
).
[
]
See also
* Trilobozoa
Trilobozoa, from Ancient Greek τρεῖς (''treîs''), meaning "three", λοβός (''lobós''), meaning "lobe", and ζῷον (''zôion''), meaning "animal", is a phylum of extinct, sessile animals that were originally classified into the Cnid ...
*'' Gehlingia''
* '' Albumares brunsae''
* '' Anfesta stankovskii''
* List of Ediacaran genera
The existence of life, especially that of animals, before the Cambrian had long been the subject of debate in paleontology. The apparent suddenness of the Cambrian explosion had no firm explanation, and Charles Darwin himself recognized the chal ...
* Triskelion
A triskelion or triskeles is an ancient motif consisting either of a triple spiral exhibiting rotational symmetry or of other patterns in triplicate that emanate from a common center. The spiral design can be based on interlocking Archimedean s ...
References
External links
Palaeos dendrogram
University of Bristol
Anatomical Information Content in the Ediacaran Fossils and Their Possible Zoological Affinities
Jerzy Dzik
Jerzy Dzik (born 25 February 1950) is a Polish paleontologist.
He has described many species, genera, and families of conodonts, including the Order (biology), order Ozarkodinida (in 1976).
In 2003, he described the Dinosauriformes, dinosaurifor ...
, Instytut Paleobiologii PAN, Twarda 51/55, 00-818 Warszawa, Poland
{{Taxonbar, from1=Q2210059, from2=Q20719482
Trilobozoa
Monotypic prehistoric animal genera
Ediacaran life
Fossils of Australia
Fossils of Russia
White Sea fossils