''Thectardis avalonensis'' is a triangular-shaped member of the Ediacaran biota, dating from . The organism took the form of an elongated

cone A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines con ...

with a central depression, and its apex was anchored to the substrate.

Morphology

The fossils take the form of a

triangle A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any three points, when non- colline ...

with a central depression, suggesting that the original organism was conical. The diameter to height ratio of the

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

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. ''Thectardis'' bearing bedding surfaces also contain '' Charnia'' and '' Ivesheadia''. Thectardis avalonensis - MUSE

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 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, 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