The Ediacaran fossil ''Hallidaya'', a close relative of '' Skinnera'' lived in Belomorian (559-550 Ma) of the Late

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

period prior to the

Cambrian explosion The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...

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.

Description

The ''Hallidaya'' is a species of ''Skinnera'' which has the shape of small circular-shaped fossils preserved as a mold. They are soft-bodied creatures approximately in diameter with an average of with a height of shaped like a dome. They have three central depressions that are connected to smaller pouch-shaped depressions around the perimeter of the disk by canals. The center depressions are speculated to be their stomach.

Environmental conditions

During the Belomorian of the Late

other organisms who lived on the ocean floor diversified their appearances through frondomorphs, tribrachiomorphs, and bilateralomorphs. Also vendobionts began migrating from the inner shelf into higher energy environments. Hallidaya became extinct in the Kotlinian (550-540 Ma) of the Late

after there was an increase of migration to high-energy areas by burrowing animals. These Ediacaran organisms were progressively outcompeted by

bilaterians The Bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly an ...

who anchored into the microbial mat of the ocean floor with their basal bulbs and possibly evolved a symbiosis with photoautotrophic or chemoautophrophic microorganisms. There were also Ediacara fan-shaped sets of paired scratches found from the Eidacara Member of the Rawnsley Quartzite in South Australia, ''Kimberichnus teruzzii''. This fossil showed signs of a ''Kimerella quadrata's'' trace maker whose death occurs at the same time as the mat excavation traces in South Australia and Russia. Their co-occurrence and systematic feeding traces in the Ediacara biota record supports the theory that bilaterians existed globally before the

Taxonomy

The Hallidaya is a genus of the

Trilobozoa ''Trilobozoa'' (meaning "three-lobed animals") is a phylum of extinct mobile animals that were originally classified into the Cnidaria. The basic body plan of ''Trilobozoa'' is often a tri-radial or radial sphere-shaped form with lobes radiating ...

taxon, but their further relationships are

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

. These fossils were mainly disk-shaped organisms with tri-radial symmetry.

Discovery

They were found by A.L. Halliday and M.M Bruner near Mount Skinner in

Northern Territory, Australia The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aus ...

. They marked off three locations and labelled them Mt. Skinner No. 1-3. Most of the fossils found were discovered between locations Mt. S2 and Mt. S3. These fossils were given to Mary Wade who worked in the Department of Geology at the University of Adelaide. Wade was able to separate the fossils into two types, Form A and Form B with there being twice as many fossils that conformed to Form A when compared to Form B. Wade named Form A ''Hallidaya brueri'' and Form B ''Skinnera brooksi''.

Taphonomy

The fossils were found flattened in a bedding of maroon and green shale with subgreywacks, impure siltstone, and claystones. They were parallel to the bedding plane and emerged with their dorsal surface facing upwards.

References

External links

Fossil Works Taxon Info
{{Taxonbar, from=Q21231169 Trilobozoa Permian first appearances Triassic extinctions Ediacaran life