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Description

Coming back further in a point in time before the Phanerozoic, far of the 550 million year line though the deep geological time, the world was totally alien to our current state of very prolific life that we know of, a planet of chaos and extreme variations in geological, climatic and chemical ways due to the major changes coming in great waves of events inside the planet surface and outside it though millions of years, at least some 4 billion years of history, most of which we are still having yet to fully understand for the scarcity of the evidence from those ancient ages, but of what we have at least a more or less clear picture of what happened. Although life did start almost after the earth crust formed and water started to flow it wouldn’t be until oxygen levels began to rise that lifeforms modified their cellular structure to take advantage of new gases and thus benefit metabolically, eventually resulted in the emergence of organisms as we know them today and even though this history is interesting to learn for this entry is going to be summarized most of this.

We pass through the first identifiable ages of earth, the Hadean and Archean with the formation of our planet and subsequently the birth of the moon by the collision of Theia some 4.5 Ga, then the cooling of the surface and formation of the oceans, the development of the first continents, and eventually the rise of life which has been estimated to have evolved more or less just after the cooling of the planet. This early life was formed by Prokaryote bacteria, living from the anaerobic conditions of earth feeding on the chemicals they could gather on the water and metabolize, but for hundreds of millions of years and becoming peak just at the end of the Archean the photosynthetic cyanobacteria would change such conditions by saturating the atmosphere with oxygen, the process was slow for some time for the chemical reactions but this when it oversaturated most of the atmosphere it killed most of the predominant anaerobic life, giving space for another wave of organisms to dominate this new world, better suited for aerobic metabolism which would open them the path for major biological developments. From here, we enter to the Proterozoic, an eon that started some 2500 million years ago and would end around 541 million years ago, this would be the major period of development of life.

It begun with the Paleoproterozoic era (2500-2000 Mya) with great continental drift movements, climatic changes and biological evolutionary events happening, including the “Great Oxidation Event” that oversaturated the atmosphere with oxygen in great amounts which probably caused a mass extinction of most Anaerobic lifeforms and believe to be correlated a great glacial period that covered most of the surface of the planet, but this would lead to the eventual evolution of more complex life though the oceans after. The first eukaryotes may have evolved during this era and thanks to the rise of oxygen were able to thrive, which correlated considerable as well with the rise of some noticeable large multicellular organisms comparable to the microscopic and unicellular congregations of microbial mats and colonies.

Found as far as 2.3 to 2.1 Ga., the Francevillian biota is represented a multitude pyrite preserved fossils which shown some of the oldest sample of macroscopic sized life with varieties of body shape, none of them related to any living clade today they were extraterrestrial in nature. (Although is still disputed wherever or not they belong to complex pluricellular life or they are sort of microbial colonies, or even more they are not remains of living organisms, until a study shown the abiotic or microbial nature of these I'm going to treat them like multicellular organisms)

Some of the current forms known include strange radial “Fried eggs” shaped forms that are among the biggest with sizes up to 12 cm and were something similar to the benthos species that would thrive on the Ediacaran, some were strange “tailed flowers” which were among the longest with sizes going up to 17 cm to some 40 cm, as well “Coins” that are tetra-radial round domes of 4 cm.

These would exist in a time span of 300 million years until a drop on oxygen levels would cause anoxia events that exterminate them all, leaving clean the oceans once again devoid of similar organisms (at least of what the fossil record can tell, there is chance some other unique biotas evolved after but weren’t able to survive preservation).

Earth eventually passed through some relative planetary stabilization in an informal period of very low changes known as “The Boring Billion” called for the timespan it lasted (from 1.8 to 0.8 Ga) being characterized by little variations on tectonic and climatic changes with all landmasses fused in a major supercontinents, being the first formed known Columbia, extended though the equator and tropics with a more or less warm climate, at least of what the geological record can tell as subsequent snowball earths would erase most of the evidence. Even though there were little variations with the current conditions, life didn’t stop evolving and keep modifying. Prokaryotes for the harsh conditions regained their position as the dominant life on the oceans as well were able to colonize land in the form of microbial mats that grew up on the rocks, meanwhile Eukaryotes still existed but enduring as the drop on oxygen levels and scarcity of key molecules and nutrients slowed down greatly their evolutionary development, but this didn’t stop them as they were able to make some remarkable development being the evolution of the main “kingdoms”, with the last ancestors of plants and animals and fungi diverge some 1.6 Ga.

In the Mesoproterozoic (1.6-1.0 Ga) Earth had some significant continental changes including the breakup of Columbia and the eventual formation of Rodinia at the end of this time lapse; oxygen levers started to rise again but slowly, stromatolites formations had its major peak in diversity no comparable to any other period, and eukaryotes were still diversifying with now the last ancestor of Animalia and fungi diverging some 1.5 Ga. With the current material collected though this period we know there was some advancement on multicellular evolution, some interesting grow up on size compared to the more minuscule life though this period, most of them sessile in nature.

-Remains from 1.56 Ga ago on the Gaoyuzhuang formation, these are elongated fronds with varied shapes, one specimen was able to reach dimensions up to 28.6 cm in height and 7.6 cm in width, even being probably even longer than 30 cm, the nature of these organisms is assumed to be algae-like being autotrophic, but still unrelated to any living clade and were part of a extinct branch of multicellular beings.

-Filamentous structures corresponding to some Macro algae of the genus Grypania spiralis that reached some 9 cm in length and a diameter of just 1 mm, forming coined forms of 3 cm in diameter, although there are some descriptions from Indian specimens of around 1.45 Ga filament reaching some 50 cm in length.

-Alongside some 1.2 to 1 Ga under the sand grew some colonial organisms known as Horodyskia, considered to be related to fungi they were formed by round or bulbous shaped tubers that protruded from the sand, all interconnected by a series of tubular “roots”, depending of the species and probably age they had a varied size but some of the biggest specimens that belongs to H. moniliformis are around 1 cm in diameter and 2 cm in height.

It wouldn’t be until the end of the Boring billion things would start to become even more interesting, with the beginning of the Neoproterozoic, on the Tonian period (1000-720 Mya) as oxygen levels started to rise and with it eukaryotes were diversifying into more macroscopic forms, most of current metazoan groups divisions can be more or less tracked back though this moment of time with some identifiable fossil organisms of considerable size, but is on the Cryogenian period (720-635 Mya) where things were going to change as the ocean surface was greatly covered by ice sheets in a double episodes of prominent glacial periods in a new “Snowball earth” event which would have caused a great disturbance on the still developing biotas, in this point life evolved greatly as first known animals like sponges, different kinds of algae and other photosynthetic eukaryotes appeared as well heterotrophic plankton at the end of the period.

After that, we enter to the final stage on life evolution which would lead to the development of the world we all know, although during this time the existing life was still strange. The Ediacaran (635-541 Mya) was the last period of the Neoproterozoic, as well the end of the Proterozoic eon, suffering heavy changes in geographical, geological and biological levels, as climate started to warm and the episode of snowball earth ended, life flourished all over the oceans in a burst of diversity of shapes and forms into what is often referred as the “Ediacaran biota”, currently is an artificial term used to group the selection of different organisms that lived through this age (specially for the last 30 million years) all characterized by their strange body arrangements of fractal nature, most of these had segmented body parts with very simple external anatomies, not specific organs more than the digestive or lacking these and being high segmented. They are among the best known of all the pre-Phanerozoic fossil record with very good quality material in different deposit sites across the world, although they keep being a bit cryptic and still need further studies. This kind of fauna at the end of the Proterozoic had become extinct due to the eventual environmental and food chain dynamic changes that triggered evolutionary pressures that this biota wouldn’t be able to adapt, leaving the room for the eventual diversification of the “Cambrian Explosion”.

Right now the affinity of most current Ediacaran fauna is still difficult to classify and with varied disputed relationships, although most of these organisms are considered to be metazoans. For the moment to make a properly overview of each variant size I had to group them under a classifications based on body shape which will be paraphyletic in most cases.

We start with the major benthonic group, the Proarticulata, a bilateral body kind of organisms which were characterized for growing a large amount of segmentation across their bodies; these elements are called Isomer which isn’t totally aligned with the opposite one, i.e., the segments intercalates with a little displacement, the number of these seems to increase depending of the age as well the number vary of species.

Diplurozoas are the most characteristic organisms found across the fossil record of the Ediacaran, their bodies are subradial and entirely divided by isomeres, being almost uniform, the isomers extends from a single original “head” which is reduced during growing becoming indistinguishable during maturity. Most shapes of these vary from oval, circular and elongated probably corresponding different methods of feeding as between the isomeres digestive pockets were located and based from trace fossils they were able to craw though the seabed being mobile. This group was formed by different species which one of the best known is Dickinsonia, especially for the common individuals of D. costata with specimens of these have variable sizes smaller individuals of few centimeters to the largest that come close to 20 cm long. However, some of largest individual known of this genus comes from other species specimen, D. rex, as this reaches some 90 to 100 cm in length, making it one of the biggest Ediacaran as well Proterozoic organisms known.

Cephalozoans are called that way for possessing a major anterior part or “head” which break the segmentation of the body leaving more evidently the asymmetry of the isomeres and gave them a more arthropod/annelid looking. The most spotted member of this group is Spriggina floundersi with a size of 5 cm, which has been classified as an arthropod or an annelid, but this actually lacks any key feature that could tie into relate them to any of the previous clades making it more likely it just convergent evolved this shape, although the longest species of this clade belongs to Yorgia waggoneri which was rounded with a prominent curved “head” was able to reach 25 cm.

Rangeomorphs are among the most successful sessile lifeforms of this period being cosmopolitan within the deep seabed of the Ediacaran oceans, they externally resemble in shape to some sessile invertebrates like sea-pens but from there looking closer to the details they are totally different to these animal, they are structured in branchiate fractal fronds which intercalated together inside the branches of the leave like structure, they were mostly attached to the ground by a simple semi flat or rounded holdfast as an anchor. Although most specimens of different species were short in height reaching some less than some centimeters, there were other species with heights of decimeters with some remarkable tall species such as Arborea arborea (once referred as a species of Charniodiscus) was able to reach a height of 60 to even a meter; as well mentions of even larger specimens reaching 2 meters.

Alongside it there was Charnia masoni a more slender frond species which is among the first species identified of being Precambrian on origin, though most specimens range from size of less than 10 to 25 cm in height, there are large and fairly well preserved specimens of individuals of impressive length, of the largest specimen scaled up with other more complete and similar large individual gives a max size of 1.85 m tall although they were thin compared to the previous genus mentioned, with a width of less than 20 cm.

Erniettomorphs are another of the weird sessile group but unlike Rangeomorphs they don’t weren’t only limited elongated fractal fronds but very varied in different body shape from anemone/clam-like (Ernietta) to upright and multiple axis fronds (Swarpuntia), from these Pteridinium stands with its strange elongated tri-radial lobed body, sunk into the sand and very flexible, it was able to bend in different degrees, some specimens of this clade were able to reach lengths up to 30 cm.

Trilobozoans were a strange group of minuscule semi-flat disc forms that existed though the seabed having different arrangements of lobes forming spirals or straight lines towards the center of the body, in most cases showing tri-radial symmetrical, the reason of why these species evolved such shapes are probably related to different ontogenic development and most likely in the feeding method as the form on how their arm arrangements influenced the water flow catching the nutrients toward their bodies, most were minuscule reaching some millimeters on size but Tribrachidium heraldicum grew to a diameter of 5 cm, with a height of around 3 cm.

There were other varieties of creatures that for the time aren’t totally assigned to a specific clade or group of this period for their specific anatomical features, as well some others specimens which could potentially be related to actual living clades, is a mix of different species which some are more stranger than others.

Kimberella quadrata is one of the most unique organisms of the period thanks to the very common fossil remains that exposed an evident complex bilateral morphology which converged to advance Protostomes like mollusks (probably making it a stem-mollusk), it had a robust oval body covered in a soft shell, in the front of the body came an elongated arrow like projection which is believed to have been the oral part that allowed it to feed on the microbial mats as well the detritus, most specimens are variable in size due to ontogeny development but some of the largest individuals are around 15 cm in length with a width of 7 cm.

Parvancorina minchami is another bilateral oddity, although more mysterious due to the simple of the body plan is more difficult to assert their possible affinity, most of the fossil specimens of these shown a varied rhomboid, elongated and shield-shaped body shapes result of different ontogenic stages, all presenting an arrow shaped ridge coming across the body. Most individuals are around 1 in length but some other can reach about 2 to 3 cm in width.

There are a selected group of sessile organisms similar to sponges identified though the Ediacaran, which although Porifera has been tracked back to almost 750 Mya using molecular clocks in general most of the species exposed only are tentative in that affinity.

-Coronacollina acula was a tri-radial sessile lifeform is among the most ancient organism with a hardened “skeleton” similar to sponges supporting its body, their size was average small as others Ediacaran organisms with a diameter of around 1 cm and a height of 5 cm, but they had a group of articulated spicules which were able to get up to 37 to 40 cm in length which used to attach to the seabed.

-Vaveliksia was a sponge-like species, known for being capsule shaped, it was attached on the seabed by a small disk-like holdfast, and some species had some degree of branches growing alongside the body, specimens of V. vana were able to reach a height of 8.6 cm and a diameter of 2 cm.

-Thectardis avalonensis is a species hinted to be possible to be a sponge for its similarities, it was a conical organisms that lived in the dark deeps of the ocean bed, with a size of 9 cm in height at average some of the biggest specimens known grew up to 16.5 cm and with a width of 9.5 cm.

Funisia dorothea was a sessile organisms being a long segmented string growing from the seabed in large groups, they shown some of the oldest evidence of sexual reproduction on animals, it had a height of about 30 cm.

Cloudina was a genus of strange long organisms characterized by their calcareous conical shells intercalated one by another forming a chain of cones when the organism was alive, is considered to be one of the earliest and most numerous sample of shelled metazoan in this period as these tend to be found in great amounts forming colonies on the seabed. Most species grew up to some centimeters in length but specimens of C. hartmannae show they could have grown up to 15 cm in length with a width of 6 mm.

Haootia quadriformis stands as a unique organisms compared to others Ediacaran, classified as a cnidarian polyp is the oldest sample of animals with muscle, as it was formed by a series of muscular fibres forming a cup shaped broad body with four-fold symmetrical arrangement, with each edge of this were attached some large branches which divided in more branches, it was attached to the seabed thanks to a stem with a disk-shaped holdfast. In total the body had a height of some 10 cm.

Ventogyrus chistyakovi was an structural oddities among Ediacaran species, once thought to be sessile and related with Trilobozoans for its tri-radial shape, some subsequent discoveries of 3D preserved individuals showed a more complex morphology architecture being this organism egg shaped with a body divided by different chambers filled by gas that maybe helped it to keep some degree of buoyancy, all connected by a series of branched canals inside, below this has a triangular axial rod with a circular part in the middle which suggests the existence of a stem where it could have been connected with the purpose cling to the bottom as a sessile organism or simply as a stabilizer as a floater, in total the size of the body of 14 cm in height and a diameter of 9 cm.

Burykhia hunti was a medium size sessile organism inhabitant of the seabed on the very end of the Paleoproterozoic, some 555 Mya, is considered to be a tunica ascidian, making it one of the oldest members of the chordates and one of our oldest close relatives of that period, the sac-shaped body seems to have been formed internally by a series of segmented and perforated bands, standing up this could have been around 15 cm tall.

References:

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-Zhu, S., Zhu, M., Knoll, A. H., Yin, Z., Zhao, F., Sun, S. ... & Liu, H. (2016). Decimetre-scale multicellular eukaryotes from the 1.56-billion-year-old Gaoyuzhuang Formation in North China. Nature communications, 7(1), 1-8.

- El Albani, Abderrazak & Bengtson, Stefan & Canfield, Donald & Bekker, Andrey & Macchiarelli, Roberto & Mazurier, Arnaud & Hammarlund, Emma & Boulvais, Philippe & Dupuy, Jean-Jacques & Fontaine, Claude & Fürsich, Franz & Gauthier-Lafaye, F. & Janvier, Philippe & Javaux, Emmanuelle & Ossa, Frantz & Pierson-Wickmann, Anne-Catherine & Riboulleau, Armelle & Sardini, Paul & Vachard, Daniel & Meunier, Alain. (2010). Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago. Nature. 466. 100-4. 10.1038/nature09166.

-Troppenz, U. M., & Littkowski, S. (2019). The Mesoproterozoic–no “boring billion”. Iranian Journal of Earth Sciences, 11(4), 239-243.

- Fedonkin, Mikhail. (2009). The origin of the Metazoa in the light of the Proterozoic fossil record. Paleontological Research. 7. 9-41. 10.2517/prpsj.7.9.

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-Retallack, G. J., Dunn, K. L., & Saxby, J. (2013). Problematic Mesoproterozoic fossil Horodyskia from Glacier National Park, Montana, USA. Precambrian Research, 226, 125-142.

- Gold, D. A. (2018). The slow rise of complex life as revealed through biomarker genetics. Emerging Topics in Life Sciences, 2(2), 191-199.

- Bobrovskiy, I., Hope, J. M., Ivantsov, A., Nettersheim, B. J., Hallmann, C., & Brocks, J. J. (2018). Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals. Science, 361(6408), 1246-1249.

- Narbonne, G. M., & Gehling, J. G. (2003). Life after snowball: The oldest complex Ediacaran fossils. Geology, 31(1), 27-30.

-Dunn, F. S., Liu, A. G., & Gehling, J. G. (2019). Anatomical and ontogenetic reassessment of the Ediacaran frond Arborea arborea and its placement within total group Eumetazoa. Palaeontology, 62(5), 851-865.

-Lipps, J. H., & Signor, P. W. (Eds.). (2013). Origin and early evolution of the Metazoa (Vol. 10). Springer Science & Business Media.

-Javaux, E. J., & Lepot, K. (2018). The Paleoproterozoic fossil record: implications for the evolution of the biosphere during Earth's middle-age. Earth-Science Reviews, 176, 68-86.

-Bottjer, D. J., & Clapham, M. E. (2006). Evolutionary paleoecology of Ediacaran benthic marine animals. In Neoproterozoic geobiology and paleobiology (pp. 91-114). Springer, Dordrecht.

- Laflamme, M., Darroch, S. A., Tweedt, S. M., Peterson, K. J., & Erwin, D. H. (2013). The end of the Ediacara biota: Extinction, biotic replacement, or Cheshire Cat? . Gondwana Research, 23(2), 558-573.

-Droser, M. L., & Gehling, J. G. (2008). Synchronous aggregate growth in an abundant new Ediacaran tubular organism. Science, 319(5870), 1660-1662.

- Fedonkin, M. A., Simonetta, A., & Ivantsov, A. Y. (2007). New data on Kimberella, the Vendian mollusc-like organism (White Sea region, Russia): palaeoecological and evolutionary implications. Geological Society, London, Special Publications, 286(1), 157-179.

-McCall, G. J. (2006). The Vendian (Ediacaran) in the geological record: enigmas in geology's prelude to the Cambrian explosion. Earth-Science Reviews, 77(1-3), 1-229.

- Evans, S. D., Gehling, J. G., & Droser, M. L. (2019). Slime travelers: Early evidence of animal mobility and feeding in an organic mat world. Geobiology, 17(5), 490-509.

-Retallack, G. J. (2007). Growth, decay and burial compaction of Dickinsonia, an iconic Ediacaran fossil. Alcheringa, 31(3), 215-240.

- Liu, A. G., Matthews, J. J., Menon, L. R., McIlroy, D., & Brasier, M. D. (2014). Haootia quadriformis n. gen., n. sp., interpreted as a muscular cnidarian impression from the Late Ediacaran period (approx. 560 Ma). Proceedings of the Royal Society B: Biological Sciences, 281(1793), 20141202.

- Fedonkin, M. A., Vickers-Rich, P., Swalla, B. J., Trusler, P., & Hall, M. (2012). A new metazoan from the Vendian of the White Sea, Russia, with possible affinities to the ascidians. Paleontological Journal, 46(1), 1-11.

-Sperling, E. A., Peterson, K. J., & Laflamme, M. (2011). Rangeomorphs, Thectardis (Porifera?) and dissolved organic carbon in the Ediacaran oceans. Geobiology, 9(1), 24-33.

-Clapham, M. E., Narbonne, G. M., Gehling, J. G., Greentree, C., & Anderson, M. M. (2004). Thectardis avalonensis: a new Ediacaran fossil from the Mistaken Point biota, Newfoundland. Journal of Paleontology, 1031-1036.

-Germs, G. J. (1972). New shelly fossils from Nama Group, south west Africa. American Journal of Science, 272(8), 752-761.

-Glaessner, M. F. (1979). Parvancorina—an arthropod from the late Precambrian (Ediacarian) of South Australia. Annalen des Naturhistorischen Museums in Wien, 83-90.

- Fedonkin, Mikhail & Ivantsov, Andrey. (2007). Ventogyrus, a possible siphonophore-like trilobozoan coelenterate from the Vendian Sequence (late Neoproterozoic), northern Russia. Geological Society, London, Special Publications. 286. 187-194. 10.1144/SP286.14.

- Ivantsov, A. Y., Malakhovskaya, Y. E., & Serezhnikova, E. A. (2004). Some problematic fossils from the Vendian of the southeastern White Sea region. PALEONTOLOGICAL JOURNAL C/C OF PALEONTOLOGICHESKII ZHURNAL, 38(1), 1-9.

- Ivantsov, A. Y. (2017). The most probable Eumetazoa among late Precambrian macrofossils. Invertebr Zool, 14(2), 127-133.

Description

Coming back further in a point in time before the Phanerozoic, far of the 550 million year line though the deep geological time, the world was totally alien to our current state of very prolific life that we know of, a planet of chaos and extreme variations in geological, climatic and chemical ways due to the major changes coming in great waves of events inside the planet surface and outside it though millions of years, at least some 4 billion years of history, most of which we are still having yet to fully understand for the scarcity of the evidence from those ancient ages, but of what we have at least a more or less clear picture of what happened. Although life did start almost after the earth crust formed and water started to flow it wouldn’t be until oxygen levels began to rise that lifeforms modified their cellular structure to take advantage of new gases and thus benefit metabolically, eventually resulted in the emergence of organisms as we know them today and even though this history is interesting to learn for this entry is going to be summarized most of this.

We pass through the first identifiable ages of earth, the Hadean and Archean with the formation of our planet and subsequently the birth of the moon by the collision of Theia some 4.5 Ga, then the cooling of the surface and formation of the oceans, the development of the first continents, and eventually the rise of life which has been estimated to have evolved more or less just after the cooling of the planet. This early life was formed by Prokaryote bacteria, living from the anaerobic conditions of earth feeding on the chemicals they could gather on the water and metabolize, but for hundreds of millions of years and becoming peak just at the end of the Archean the photosynthetic cyanobacteria would change such conditions by saturating the atmosphere with oxygen, the process was slow for some time for the chemical reactions but this when it oversaturated most of the atmosphere it killed most of the predominant anaerobic life, giving space for another wave of organisms to dominate this new world, better suited for aerobic metabolism which would open them the path for major biological developments. From here, we enter to the Proterozoic, an eon that started some 2500 million years ago and would end around 541 million years ago, this would be the major period of development of life.

It begun with the Paleoproterozoic era (2500-2000 Mya) with great continental drift movements, climatic changes and biological evolutionary events happening, including the “Great Oxidation Event” that oversaturated the atmosphere with oxygen in great amounts which probably caused a mass extinction of most Anaerobic lifeforms and believe to be correlated a great glacial period that covered most of the surface of the planet, but this would lead to the eventual evolution of more complex life though the oceans after. The first eukaryotes may have evolved during this era and thanks to the rise of oxygen were able to thrive, which correlated considerable as well with the rise of some noticeable large multicellular organisms comparable to the microscopic and unicellular congregations of microbial mats and colonies.

Found as far as 2.3 to 2.1 Ga., the Francevillian biota is represented a multitude pyrite preserved fossils which shown some of the oldest sample of macroscopic sized life with varieties of body shape, none of them related to any living clade today they were extraterrestrial in nature. (Although is still disputed wherever or not they belong to complex pluricellular life or they are sort of microbial colonies, or even more they are not remains of living organisms, until a study shown the abiotic or microbial nature of these I'm going to treat them like multicellular organisms)

Some of the current forms known include strange radial “Fried eggs” shaped forms that are among the biggest with sizes up to 12 cm and were something similar to the benthos species that would thrive on the Ediacaran, some were strange “tailed flowers” which were among the longest with sizes going up to 17 cm to some 40 cm, as well “Coins” that are tetra-radial round domes of 4 cm.

These would exist in a time span of 300 million years until a drop on oxygen levels would cause anoxia events that exterminate them all, leaving clean the oceans once again devoid of similar organisms (at least of what the fossil record can tell, there is chance some other unique biotas evolved after but weren’t able to survive preservation).

Earth eventually passed through some relative planetary stabilization in an informal period of very low changes known as “The Boring Billion” called for the timespan it lasted (from 1.8 to 0.8 Ga) being characterized by little variations on tectonic and climatic changes with all landmasses fused in a major supercontinents, being the first formed known Columbia, extended though the equator and tropics with a more or less warm climate, at least of what the geological record can tell as subsequent snowball earths would erase most of the evidence. Even though there were little variations with the current conditions, life didn’t stop evolving and keep modifying. Prokaryotes for the harsh conditions regained their position as the dominant life on the oceans as well were able to colonize land in the form of microbial mats that grew up on the rocks, meanwhile Eukaryotes still existed but enduring as the drop on oxygen levels and scarcity of key molecules and nutrients slowed down greatly their evolutionary development, but this didn’t stop them as they were able to make some remarkable development being the evolution of the main “kingdoms”, with the last ancestors of plants and animals and fungi diverge some 1.6 Ga.

In the Mesoproterozoic (1.6-1.0 Ga) Earth had some significant continental changes including the breakup of Columbia and the eventual formation of Rodinia at the end of this time lapse; oxygen levers started to rise again but slowly, stromatolites formations had its major peak in diversity no comparable to any other period, and eukaryotes were still diversifying with now the last ancestor of Animalia and fungi diverging some 1.5 Ga. With the current material collected though this period we know there was some advancement on multicellular evolution, some interesting grow up on size compared to the more minuscule life though this period, most of them sessile in nature.

-Remains from 1.56 Ga ago on the Gaoyuzhuang formation, these are elongated fronds with varied shapes, one specimen was able to reach dimensions up to 28.6 cm in height and 7.6 cm in width, even being probably even longer than 30 cm, the nature of these organisms is assumed to be algae-like being autotrophic, but still unrelated to any living clade and were part of a extinct branch of multicellular beings.

-Filamentous structures corresponding to some Macro algae of the genus Grypania spiralis that reached some 9 cm in length and a diameter of just 1 mm, forming coined forms of 3 cm in diameter, although there are some descriptions from Indian specimens of around 1.45 Ga filament reaching some 50 cm in length.

-Alongside some 1.2 to 1 Ga under the sand grew some colonial organisms known as Horodyskia, considered to be related to fungi they were formed by round or bulbous shaped tubers that protruded from the sand, all interconnected by a series of tubular “roots”, depending of the species and probably age they had a varied size but some of the biggest specimens that belongs to H. moniliformis are around 1 cm in diameter and 2 cm in height.

It wouldn’t be until the end of the Boring billion things would start to become even more interesting, with the beginning of the Neoproterozoic, on the Tonian period (1000-720 Mya) as oxygen levels started to rise and with it eukaryotes were diversifying into more macroscopic forms, most of current metazoan groups divisions can be more or less tracked back though this moment of time with some identifiable fossil organisms of considerable size, but is on the Cryogenian period (720-635 Mya) where things were going to change as the ocean surface was greatly covered by ice sheets in a double episodes of prominent glacial periods in a new “Snowball earth” event which would have caused a great disturbance on the still developing biotas, in this point life evolved greatly as first known animals like sponges, different kinds of algae and other photosynthetic eukaryotes appeared as well heterotrophic plankton at the end of the period.

After that, we enter to the final stage on life evolution which would lead to the development of the world we all know, although during this time the existing life was still strange. The Ediacaran (635-541 Mya) was the last period of the Neoproterozoic, as well the end of the Proterozoic eon, suffering heavy changes in geographical, geological and biological levels, as climate started to warm and the episode of snowball earth ended, life flourished all over the oceans in a burst of diversity of shapes and forms into what is often referred as the “Ediacaran biota”, currently is an artificial term used to group the selection of different organisms that lived through this age (specially for the last 30 million years) all characterized by their strange body arrangements of fractal nature, most of these had segmented body parts with very simple external anatomies, not specific organs more than the digestive or lacking these and being high segmented. They are among the best known of all the pre-Phanerozoic fossil record with very good quality material in different deposit sites across the world, although they keep being a bit cryptic and still need further studies. This kind of fauna at the end of the Proterozoic had become extinct due to the eventual environmental and food chain dynamic changes that triggered evolutionary pressures that this biota wouldn’t be able to adapt, leaving the room for the eventual diversification of the “Cambrian Explosion”.

Right now the affinity of most current Ediacaran fauna is still difficult to classify and with varied disputed relationships, although most of these organisms are considered to be metazoans. For the moment to make a properly overview of each variant size I had to group them under a classifications based on body shape which will be paraphyletic in most cases.

We start with the major benthonic group, the Proarticulata, a bilateral body kind of organisms which were characterized for growing a large amount of segmentation across their bodies; these elements are called Isomer which isn’t totally aligned with the opposite one, i.e., the segments intercalates with a little displacement, the number of these seems to increase depending of the age as well the number vary of species.

Diplurozoas are the most characteristic organisms found across the fossil record of the Ediacaran, their bodies are subradial and entirely divided by isomeres, being almost uniform, the isomers extends from a single original “head” which is reduced during growing becoming indistinguishable during maturity. Most shapes of these vary from oval, circular and elongated probably corresponding different methods of feeding as between the isomeres digestive pockets were located and based from trace fossils they were able to craw though the seabed being mobile. This group was formed by different species which one of the best known is Dickinsonia, especially for the common individuals of D. costata with specimens of these have variable sizes smaller individuals of few centimeters to the largest that come close to 20 cm long. However, some of largest individual known of this genus comes from other species specimen, D. rex, as this reaches some 90 to 100 cm in length, making it one of the biggest Ediacaran as well Proterozoic organisms known.

Cephalozoans are called that way for possessing a major anterior part or “head” which break the segmentation of the body leaving more evidently the asymmetry of the isomeres and gave them a more arthropod/annelid looking. The most spotted member of this group is Spriggina floundersi with a size of 5 cm, which has been classified as an arthropod or an annelid, but this actually lacks any key feature that could tie into relate them to any of the previous clades making it more likely it just convergent evolved this shape, although the longest species of this clade belongs to Yorgia waggoneri which was rounded with a prominent curved “head” was able to reach 25 cm.

Rangeomorphs are among the most successful sessile lifeforms of this period being cosmopolitan within the deep seabed of the Ediacaran oceans, they externally resemble in shape to some sessile invertebrates like sea-pens but from there looking closer to the details they are totally different to these animal, they are structured in branchiate fractal fronds which intercalated together inside the branches of the leave like structure, they were mostly attached to the ground by a simple semi flat or rounded holdfast as an anchor. Although most specimens of different species were short in height reaching some less than some centimeters, there were other species with heights of decimeters with some remarkable tall species such as Arborea arborea (once referred as a species of Charniodiscus) was able to reach a height of 60 to even a meter; as well mentions of even larger specimens reaching 2 meters.

Alongside it there was Charnia masoni a more slender frond species which is among the first species identified of being Precambrian on origin, though most specimens range from size of less than 10 to 25 cm in height, there are large and fairly well preserved specimens of individuals of impressive length, of the largest specimen scaled up with other more complete and similar large individual gives a max size of 1.85 m tall although they were thin compared to the previous genus mentioned, with a width of less than 20 cm.

Erniettomorphs are another of the weird sessile group but unlike Rangeomorphs they don’t weren’t only limited elongated fractal fronds but very varied in different body shape from anemone/clam-like (Ernietta) to upright and multiple axis fronds (Swarpuntia), from these Pteridinium stands with its strange elongated tri-radial lobed body, sunk into the sand and very flexible, it was able to bend in different degrees, some specimens of this clade were able to reach lengths up to 30 cm.

Trilobozoans were a strange group of minuscule semi-flat disc forms that existed though the seabed having different arrangements of lobes forming spirals or straight lines towards the center of the body, in most cases showing tri-radial symmetrical, the reason of why these species evolved such shapes are probably related to different ontogenic development and most likely in the feeding method as the form on how their arm arrangements influenced the water flow catching the nutrients toward their bodies, most were minuscule reaching some millimeters on size but Tribrachidium heraldicum grew to a diameter of 5 cm, with a height of around 3 cm.

There were other varieties of creatures that for the time aren’t totally assigned to a specific clade or group of this period for their specific anatomical features, as well some others specimens which could potentially be related to actual living clades, is a mix of different species which some are more stranger than others.

Kimberella quadrata is one of the most unique organisms of the period thanks to the very common fossil remains that exposed an evident complex bilateral morphology which converged to advance Protostomes like mollusks (probably making it a stem-mollusk), it had a robust oval body covered in a soft shell, in the front of the body came an elongated arrow like projection which is believed to have been the oral part that allowed it to feed on the microbial mats as well the detritus, most specimens are variable in size due to ontogeny development but some of the largest individuals are around 15 cm in length with a width of 7 cm.

Parvancorina minchami is another bilateral oddity, although more mysterious due to the simple of the body plan is more difficult to assert their possible affinity, most of the fossil specimens of these shown a varied rhomboid, elongated and shield-shaped body shapes result of different ontogenic stages, all presenting an arrow shaped ridge coming across the body. Most individuals are around 1 in length but some other can reach about 2 to 3 cm in width.

There are a selected group of sessile organisms similar to sponges identified though the Ediacaran, which although Porifera has been tracked back to almost 750 Mya using molecular clocks in general most of the species exposed only are tentative in that affinity.

-Coronacollina acula was a tri-radial sessile lifeform is among the most ancient organism with a hardened “skeleton” similar to sponges supporting its body, their size was average small as others Ediacaran organisms with a diameter of around 1 cm and a height of 5 cm, but they had a group of articulated spicules which were able to get up to 37 to 40 cm in length which used to attach to the seabed.

-Vaveliksia was a sponge-like species, known for being capsule shaped, it was attached on the seabed by a small disk-like holdfast, and some species had some degree of branches growing alongside the body, specimens of V. vana were able to reach a height of 8.6 cm and a diameter of 2 cm.

-Thectardis avalonensis is a species hinted to be possible to be a sponge for its similarities, it was a conical organisms that lived in the dark deeps of the ocean bed, with a size of 9 cm in height at average some of the biggest specimens known grew up to 16.5 cm and with a width of 9.5 cm.

Funisia dorothea was a sessile organisms being a long segmented string growing from the seabed in large groups, they shown some of the oldest evidence of sexual reproduction on animals, it had a height of about 30 cm.

Cloudina was a genus of strange long organisms characterized by their calcareous conical shells intercalated one by another forming a chain of cones when the organism was alive, is considered to be one of the earliest and most numerous sample of shelled metazoan in this period as these tend to be found in great amounts forming colonies on the seabed. Most species grew up to some centimeters in length but specimens of C. hartmannae show they could have grown up to 15 cm in length with a width of 6 mm.

Haootia quadriformis stands as a unique organisms compared to others Ediacaran, classified as a cnidarian polyp is the oldest sample of animals with muscle, as it was formed by a series of muscular fibres forming a cup shaped broad body with four-fold symmetrical arrangement, with each edge of this were attached some large branches which divided in more branches, it was attached to the seabed thanks to a stem with a disk-shaped holdfast. In total the body had a height of some 10 cm.

Ventogyrus chistyakovi was an structural oddities among Ediacaran species, once thought to be sessile and related with Trilobozoans for its tri-radial shape, some subsequent discoveries of 3D preserved individuals showed a more complex morphology architecture being this organism egg shaped with a body divided by different chambers filled by gas that maybe helped it to keep some degree of buoyancy, all connected by a series of branched canals inside, below this has a triangular axial rod with a circular part in the middle which suggests the existence of a stem where it could have been connected with the purpose cling to the bottom as a sessile organism or simply as a stabilizer as a floater, in total the size of the body of 14 cm in height and a diameter of 9 cm.

Burykhia hunti was a medium size sessile organism inhabitant of the seabed on the very end of the Paleoproterozoic, some 555 Mya, is considered to be a tunica ascidian, making it one of the oldest members of the chordates and one of our oldest close relatives of that period, the sac-shaped body seems to have been formed internally by a series of segmented and perforated bands, standing up this could have been around 15 cm tall.

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