''Ausia fenestrata'' is a curious

Ediacaran period 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 ...

(630 – 539 million years ago)

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

represented by only one specimen 5 cm long from the

Nama Group The Nama Group is a megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two ear ...

, a

Vendian 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 the ...

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

group of stratigraphic sequences deposited in the Nama foreland basin in central and southern

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

. It has similarity to ''

Burykhia ''Burykhia hunti'' is a Precambrian fossil from the White Sea region of Russia dating to . It is considered of ascidian affinity, due to the sac-like morphology and a series of distinctly perforated bands reminiscent of a tunicate pharynx. If '' ...

'' from Ediacaran (Vendian)

siliciclastic Siliciclastic (or ''siliclastic'') rocks are clastic noncarbonate sedimentary rocks that are composed primarily of silicate minerals, such as quartz or clay minerals. Siliciclasic rock types include mudrock, sandstone Sandstone is a clastic ...

sediments exposed on the Syuzma River of northern

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

. This fossil is of the form of an elongate bag-like sandstone cast (Nama-type preservation) tapering to a cone on one end. The surface of the fossil is covered with oval depressions ("windows") regularly spaced over the surface in the manner of concentric/parallel rows. The taxonomic identity of ''Ausia'' is unresolved.

Interpretations

* G. Hahn and H. D. Pflug suggested that ''Ausia'' is a pennatulacean coral from the family Veretillidae, but there are no signs of secondary polyps on the fossil, which are nonetheless represented in Hahn and Pflug's reconstruction. No veretillids are represented in the fossil record as far as is known. * Some researchers have assumed that these depressions are pores and interpreted ''Ausia'' as an ancestor of archeocyathans and other sponge-like organismsM. A. Fedonkin (1996). "Ausia as an ancestor of archeocyathans, and other sponge-like organisms". In: ''Enigmatic Organisms in Phylogeny and Evolution. Abstracts''. Moscow, Paleontological Institute, Russian Academy of Sciences, p. 90-91. or true

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

.Mark A. S. McMenamin (1998). "The Sand Menagerie". In: ''The Garden of Ediacara: Discovering the First Complex Life''. Columbia University Press. New York. pp.11-46. But

Adolf Seilacher Adolf "Dolf" Seilacher (February 24, 1925 – April 26, 2014) was a German palaeontologist who worked in evolutionary and ecological palaeobiology for over 60 years. He is best known for his contributions to the study of trace fossils; constructi ...

has argued that the "windows" are merely dimples. * ''Ausia'' may represent

ascidians Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" ...

(sea squirts), an invertebrate group related to the

chordates A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five ...

.Vickers-Rich P. (2007). "Chapter 4. The Nama Fauna of Southern Africa". In: Fedonkin M.A., Gehling J.G., Grey K., Narbonne G.M., Vickers-Rich P. ''The Rise of Animals: Evolution and Diversification of the Kingdom Animalia'', Johns Hopkins University Press. pp. 69-87 Results of a new study of a ''

'' from Russia have shown a possible affinity of these organisms to the ascidians, which are

urochordates A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

. The Russian species is more than 90 mm across, and the rows of oval depressions are separated by structures which were probably grooves in the internal wall surface of the living organism. The study's authors interpret these fossils as the internal sand casts of a vast bag-like cavity, possibly a pharynx or branchial basket.M.A. Fedonkin, P. Vickers Rich, B. Swalla, P. Trusler, M. Hall. (2008). "A Neoproterozoic chordate with possible affinity to the ascidians: New fossil evidence from the Vendian of the White Sea, Russia and its evolutionary and ecological implications". HPF-07 Rise and fall of the Ediacaran (Vendian) biota. International Geological Congress - Oslo 2008. The animals represented by these two genera were thought to live in the shallow waters of an epicontinental sea, slightly more than 555-548 million years ago, and the authors feel this is probably the oldest evidence of the chordate lineage of metazoans. * Jerzy Dzik has suggested that ''Ausia'' bears some similarity to the

halkieriid The halkieriids are a group of fossil organisms from the Lower to Middle Cambrian. Their eponymous genus is ''Halkieria'' , which has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the smal ...

s, and resembles the body plan that might be expected of halkieriid ancestors under the

coeloscleritophoran The Coelosclerithophorans are a polyphyletic group of organisms bearing hollow sclerites made of aragonite, and with a supposedly distinctive microstructure. Their skeletons may be homologous to those of the molluscs, and ''Halkieria'' looks very ...

hypothesis. Ausia3.jpg, Hahn and Pflug reconstruction of ''Ausia'' as a pennatulacean Ausia fenestra.jpg, Reconstructed as a tunicate

References

{{Taxonbar, from=Q4822760 Ediacaran life Fossils of Namibia Fossil taxa described in 1985

Interpretations

See also

References