The Avalon explosion, named from the
Precambrian fauna of the
Avalon Peninsula, is a proposed
evolutionary radiation
An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid ...
in the history of the
Animalia, about 575 million years ago in the
Ediacaran Period, with the Avalon explosion being one of three eras grouped in this time.
This event is believed to have occurred some 33 million years earlier than the
Cambrian explosion. Scientists are still unsure of the full extent behind the development of the Avalon explosion.
The Avalon explosion resulted in a rapid increase in organism diversity. Many of the animals and plants from the Avalon are found living in deep marine environments and the
Flinders Ranges
The Flinders Ranges are the largest mountain range in South Australia, which starts about north of Adelaide. The ranges stretch for over from Port Pirie to Lake Callabonna.
The Adnyamathanha people are the Aboriginal group who have inhabit ...
.
The first stages of the Avalon explosion were observed through comparatively minimal species.
History
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...
predicted a time of ecological growth before the Cambrian Period, but there was no evidence to support it until, the Avalon explosion was proposed in 2008 by
Virginia Tech
Virginia Tech (formally the Virginia Polytechnic Institute and State University and informally VT, or VPI) is a public land-grant research university with its main campus in Blacksburg, Virginia. It also has educational facilities in six re ...
paleontologists
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...
after analysis of the morphological space change in several
Ediacaran assemblages.
The discovery suggests that the early evolution of
animals
Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
may have involved more than one explosive event.
The original analysis has been the subject of dispute in the literature.
Evidence
Trace fossils of these Avalon organisms have been found worldwide, with many found in
Newfoundland, in Canada and the
Charnwood Forest in England,
representing the earliest known complex
multicellular organisms.
[Simple multicellular organisms such as red algae evolved at least .] The Avalon explosion theoretically produced the
Ediacaran biota.
The biota largely disappeared contemporaneously with the rapid increase in
biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
known as the Cambrian explosion. At this time, all living animal groups were present in the Cambrian oceans.
The Avalon explosion appears similar to the Cambrian explosion in the rapid increase in diversity of
morphologies in a relatively small-time frame, followed by diversification within the established
body plan
A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.
This term, usually applied to animals, envisages a "blueprin ...
s,
a pattern similar to that observed in other evolutionary events.
Plants and Animals
The Avalon explosion was a time of early evolution and low diversity in species. There were over 270 species defined,
with 50 different morphological characteristics categories, many of which the anatomical structure had to be inferred with fossils and casts.
These species were placed into 20 different genera.
During this time, animals became bilateral and along with increasing complexity.
Many animals during this time fit into the
annelid,
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
,
echinoderm
An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...
, and
cnidarian phyla.
Animals at this time developed bilateral symmetry with a clear anterior and posterior side, which included species like ''
Springgina'', ''
Charniodiscus
''Charniodiscus'' is an Ediacaran fossil that in life was probably a stationary filter feeder that lived anchored to a sandy sea bed. The organism had a holdfast, stalk and frond. The holdfast was bulbous shaped, and the stalk was flexible. Th ...
'' and ''
Yorgia
''Yorgia waggoneri'' is a discoid Ediacaran organism. It has a low, segmented body consisting of a short wide "head", no appendages, and a long body region, reaching a maximum length of . It is classified within the extinct animal phylum Proarti ...
''.
Along with many of the plants fitting into a now-extinct phylum of
Vendobionta
Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, i ...
.
The Vendobionta were radically arranged, with many tubular elements and a central stalk. With ''
frondlets'' were a prominent aquatic plant during this time, with many different shapes, including ''
fractofusus'' which is a spindle shape, ''
bradgatia
''Bradgatia linfordensis'' is a bush-like Ediacaran fossil. It consists of six or more fronds radiating from a central anchor point at the base. It superficially resembles a compressed cabbage in appearance, although in reality it had a more ...
'', a lettuce shape; and
rangea
''Rangea'' is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.
''Rangea'' was the first complex Precambrian macrofossil named and described anywhere in the world. ''Rangea'' was a centimetre- ...
which was a left shape.
See also
*
Cambrian Explosion
*
Great Ordovician Biodiversification Event
The Great Ordovician Biodiversification Event (GOBE), was an evolutionary radiation of animal life throughout the Ordovician period, 40 million years after the Cambrian explosion, whereby the distinctive Cambrian fauna fizzled out to be replaced ...
*
Carboniferous-Earliest Permian Biodiversification Event
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
Notes
References
{{reflist
Evolution of the biosphere
Unsolved problems in biology
Ediacaran life
Biological hypotheses