The Ediacaran biota consisted of enigmatic tubular and frond-shaped, mostly sessile organisms that lived during the Ediacaran Period. Trace fossils of organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The Ediacaran biota radiated in an event called the Avalon explosion,575 million years ago, the biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion. Most of the existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have replaced the organisms that dominated the Ediacaran fossil record. Multiple hypotheses exist to explain the disappearance of this biota, including bias, a changing environment. The morphology and habit of some taxa suggest relationships to Porifera or Cnidaria, Kimberella may show a similarity to molluscs, and other organisms have been thought to possess bilateral symmetry, although this is controversial. Most macroscopic fossils are morphologically distinct from later life-forms, they resemble discs, tubes, one palaeontologist proposed a separate kingdom level category Vendozoa in the Linnaean hierarchy for the Ediacaran biota. The concept of Ediacaran Biota is, of course, somewhat artificial as it can not be defined geographically, stratigraphically, taphonomically, the first Ediacaran fossils discovered were the disc-shaped Aspidella terranovica in 1868. Their discoverer, Scottish geologist Alexander Murray, found them useful aids for correlating the age of rocks around Newfoundland, instead, they were interpreted as gas escape structures or inorganic concretions. No similar structures elsewhere in the world were known and the one-sided debate soon fell into obscurity. It was not until the British discovery of the iconic Charnia in 1957 that the pre-Cambrian was seriously considered as containing life. This frond-shaped fossil was found in Englands Charnwood Forest, and due to the geological mapping of the British Geological Survey there was no doubt these fossils sat in Precambrian rocks. All specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, poor communication, combined with the difficulty in correlating globally distinct formations, led to a plethora of different names for the biota. Ediacaran and Ediacarian were subsequently applied to the epoch or period of geological time, in March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming the terminal period of the Neoproterozoic after the Australian locality. The term Ediacaran biota and similar has, at times, been used in a geographic, stratigraphic, taphonomic, or biological sense. Microbial mats are areas of sediment stabilised by the presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a layer of sediment but this is an illusion caused by the colonys growth, individuals do not, themselves
Dickinsonia costata, an iconic Ediacaran organism, displays the characteristic quilted appearance of Ediacaran enigmata.
Palaeontologist Guy Narbonne examining Ediacaran fossils in Newfoundland