''Thectardis avalonensis'' is a triangular-shaped member of the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-sh ...

, dating from . The organism took the form of an elongated cone with a central depression, and its apex was anchored to the substrate.

Morphology

The

fossils 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 in ...

take the form of a triangle with a central depression, suggesting that the original organism was conical. The diameter to height ratio of the organism is roughly constant in each location at 1 to 3 in the younger beds, and from 1 to 2.5 in the older beds. The constant ratio suggests that it grew by adding to its body at the base of the cone. The triangle has a raised margin about a quarter of the width of the triangle. The interior either is blank, depressed, or has some vague transverse markings. The impression occurs in the upper bed rather than the lower surface.

Occurrence

205 specimens of ''Thectardis'' are known, from two bedding surfaces, separated by 2 km and 10 million years at

Mistaken Point Mistaken Point Ecological Reserve is a wilderness area and a UNESCO World Heritage Site located at the southeastern tip of Newfoundland's Avalon Peninsula in the Canadian province of Newfoundland and Labrador. The reserve is home to the namesak ...

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

. ''Thectardis'' bearing bedding surfaces also contain ''

Charnia ''Charnia'' is a genus of frond-like lifeforms belonging to the Ediacaran biota with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture (thus exhibiting glide reflection, or opposite isometry). T ...

'' and ''

Ivesheadia The "ivesheadiomorphs" are a group of fossilised structures known from Ediacaran localities in England and Newfoundland. They are considered to be taphomorphs, representing the poorly preserved biological remains of various contemporary taxa suc ...

''.

Ecology

Water currents knocked down the triangles in the same direction, and where they fall on top of other objects they flex over the top. When alive, the organism probably stuck to the microbial mats that bound the

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 ...

sea floor, standing on their tips like a pin in a pin cushion, so that the organism would have resembled an inverted cone. They probably fed on suspended particles. As there is no evidence for a holdfast anchoring them to the sea floor, it remains a matter of speculation how they were attached.

Etymology

The generic name ''Thectardis'' is derived from the Greek ''thektos'', sharp-pointed, and ''ardis'', arrow-point. The specific name derives from the

Avalon Peninsula The Avalon Peninsula (french: Péninsule d'Avalon) is a large peninsula that makes up the southeast portion of the island of Newfoundland. It is in size. The peninsula is home to 270,348 people, about 52% of Newfoundland's population, according ...

, where it was found. Thus, ''Thectardis avalonensis'' translates as "sharp arrow-point of Avalon (Peninsula)."

References

* {{Taxonbar, from=Q7777663 Ediacaran life Ediacaran Canada Enigmatic prehistoric animal genera Fossil taxa described in 2004

Morphology

Occurrence

Ecology

Etymology

See also

References