EDIACARA FAUNA: ORIGIN, CHARACTERISTICS AND EXTINCTION - BIOLOGY - 2025

The Ediacara fauna is a set of organisms that represent the different species that lived on Earth during the Ediacara geological period, about 600 million years ago. Its origin may be associated with the global increase in atmospheric oxygen levels.

This fact favored the development of primitive metazoans, characterized by having very diverse shapes and a soft body. Ediacara fauna is found in a paleontological site discovered in 1946 by Reginald Sprigg in Australia's Ediacara Mountains.

Ediacara fauna. Source: Ryan Somma, via Wikimedia Commons

The fossil records of this fauna are preserved in several regions of the world (except Antarctica). Some of these places are the White Sea coast in Russia, Namibia, Newfoundland, and the MacKenzie Mountains in Canada. There are also samples in the Flinders Range, located in South Australia.

According to some specialists, this fauna represents an important development of multicellular animals before the Cambrian explosion. The Ediacara fauna was one of the first life forms that required atmospheric oxygen for its development; in addition, it is considered a precursor of skeletal organisms.

Origin

The history of planet Earth probably started 4.55 billion years ago. Thousands of years later, in the Neo-Archean era, the presence of stromatolites adhered to the substrate shows the existence of free oxygen in the terrestrial environment.

However, it was not until the Proterozoic that there was a complete transition to an oxygenated atmosphere. The last stage of the Neoproterozoic era is known as the Ediacaran period.

The beginning of this geological period was 635 million years ago and ended 542 million years ago. At this time, the oldest known multicellular organisms lived, such as the first sponges and anemones.

Lack of previous fossils

A possible explanation for the lack of ancestor fossils may be that, prior to the multicellular phase of Ediacaran, beings lacked collagen, a fibrous protein that strengthens the animal's body and allows its conservation.

This organic compound is only produced when the level of atmospheric oxygen is greater than 3%, which possibly occurred on Earth at the time of the Ediacaran fauna.

Evidence of this biota has been found in various regions of the world. Its irradiation could have occurred during the Avalon explosion, 575 million years ago.

Relationship with modern fauna

There are two theories regarding the affinity between the Ediacara fauna and the current forms of living beings.

One hypothesis is that most are direct ancestors of the species that are known today. The other posits that the Ediacara biota is an isolated evolution, with no connection to any current living form. For this reason they were grouped into a separate phylum: the extinct Vendozoa.

However, evaluation of the fossils shows that some Ediacara species are similar to those that existed in the Cambrian. Similarly, some may be related to current organisms. For example, the Kimbelerra cuadrata - a species that lived in the Ediacaran period - shows a strong resemblance to mollusks.

Although these approaches may seem contradictory, the existence of the Ediacaran biota could be the evolutionary explanation for some modern species.

characteristics

The fossils found at the Ediacara paleontological site were formed when they were covered by the mud of the seabed and by the fine sand. In this way depressions were created in the underlying sand bodies.

Since the mud contained a high percentage of water, as it dried, the thickness of the bed decreased, giving the fossils a flattened and rounded outline. Due to this, it is presumed that the fauna has a benthic bias instead of being made up of free-swimming forms, as previously believed.

They are presumed to have lived near shallow continental shelf sediments. They were also able to inhabit the depths of the continental margins that existed in that prehistoric time.

Reproduction

Some impressions found in the rocks of the Ediacara deposit have enriched the knowledge on aspects related to the reproduction of the fauna of that geological period.

Fractofusus fossils were found in colonies, grouped by size: large, medium and small. Because of this, the researchers suggest that these organisms had complex reproduction.

Some of these were able to reproduce by asexual or sexual spores, which spread to other areas through the water. Others could have spread asexually, through stolons.

The inference of the existence of various reproductive modes in Fractofusus could suggest a complex life that allowed them to colonize various habitats efficiently.

Size and shape of fossils

The Ediacara fossil records were derived from organisms that had a soft body. These prints have a great diversity of shapes: they exist in the form of discs formed by concentric ribbed structures, by internal radials or by a combination of both.

Irregular amorphous masses and fronds were also found, which presumably could have belonged to primitive structures of the sporophytes.

The rounded fossils are a few centimeters in diameter, although some can measure up to 20 centimeters. Frond-like prints can be long - up to about one meter.

The vast majority of fossils are rounded in shape, similar to that of jellyfish. Other forms include elongated organisms grouped in colonies, very similar to today's marine feathers.

Flattened and segmented organisms were also found, which may be associated with the group of annelids. Additionally, some samples were from animals with leg-like structures, implying that they may be possible ancestors of arthropods.

Extinction

It was previously stated that the Ediacaran fauna became completely extinct at the end of the Precambrian, possibly due to the heavy grazing of primitive animals and the variations in sea level that occurred at that time.

However, recent discoveries and research confirm that some Ediacaran species lived during the Cambrian period.

Several hypotheses try to explain the extinction of the Ediacara biota. Some of these are as follows:

Glaciations

The periods of intense cold could be a barrier for the multicellular organisms to continue to develop. Some species appeared almost a million years after Earth emerged from a natural global glaciation event.

However, the diversity of living things in Antarctica raises questions about whether low temperatures actually decrease or increase the rate of evolution.

Predation

In the early Cambrian period, organisms at the top of the food chain (such as Kimberella) were predators of microbes. If this predation began during the decline of the Ediacaran fauna, it could have led to the extinction of several species.

It may also have happened that some animals fed directly on the Ediacara biota, contributing to the decline of the members of that population.

Environmental variations

At the end of the Precambrian and at the beginning of the Cambrian, great geological, climatic and biological changes occurred that caused enormous variations in the composition of the atmosphere and the other components of the ecosystem.

This stage is known as the Cambrian explosion, when several multicellular organisms appeared, diversified and radiated.

Although it may be difficult to infer the effect of these changes on the disappearance of the Ediacaran biota, the variation in oxygen levels, the separation of supercontinents, and changes in the composition and level of the oceans may have played a role. very important.

References

1. Brian F. Windley (2019).Ediacara fauna. Fossil assemblage, Australia Recovered from britannica.com.
2. Wikipedia (2018).Ediacaran biota. Recovered from en.wikipedia.org.
3. Guy M. Narbonne (2005). The Ediacara biota: Neoproterozoic Origin of Animals and Their Ecosystems. Annual Review of Earth and Planetary Science. Recovered from pages.geo.wvu.edu.
4. H. Monroe (2014). Australia: The Land Where Time Began. Ediacara fauna. Recovered from austhrutime.com.
5. The burgess shale (2011). Engmantic Ediacarans. Royal Ontario Museum. Recovered from burgess-shale.rom.on.ca.
6. Breandán Anraoi MacGabhann (2014). There is no such thing as the 'Ediacara Biota'. Science direct. Recovered from sciencedirect.com
7. Marc Laflamme, Simon AF Darroch, Sarah M. Tweedt, Kevin J. Peterson, Douglas H. Erwin (2013). The end of the Ediacara biota: Extinction, biotic replacement, or Cheshire Cat ?. Science direct. Recovered from sciencedirect.com.
8. Marc Laflamme Simon, AF Darroch (2015). Palaeobiology: Ecological Revelations in Ediacaran Reproduction. Science direct. Recovered from sciencedirect.com.