Description

Late Precambrian (Vendian)
Penega Formation
East Angelsk, White Sea, Russia
10mm highly detailed specimen on 75mm matrix.
Problematica, Ediacaran.

Tribrachidium is a genus of soft-bodied animal that some paleontologists have deemed as something like an early echinoderm but not of the same phylum, ending up in a phylum of its own, Trilobozoa.  Many researchers have left its placement in the animal kingdom as an open question.  Tribrachidium apparently died out before the beginning of the Paleozoic Era.

The Vendian Period covers a span of geologic time from about 540 to 650 million years ago, which is the most recent block of the Proterozoic Eon.  It is the time that macroscopic life appeared – best known from areas like the Ediacara Hills, Australia, Mistaken Point, Newfoundland, and the White Sea.  By the end of the Vendian the supercontinent, Rodinia, which formed from the collisions of protocontinents approximately 1.2 billion years ago, had started to fragment into continents only a geologist would recognize.  Those landmasses would reconnect at the end of the Paleozoic Era over 300 million years later.