Olson extinction

The first evidence of extinction appeared when noticed a sharp transition from the Early Permian faunas, which were dominated by pelicosaurs and therapsids , to the fundamentally different faunas of the Middle and Late Permian. At first, the scientists considered the absence of transitional faunas to be due to the fact that their remains were simply not preserved in the fossil record, and applied the term “Olson gap” to the abrupt transition, referring precisely to the absence of extant paleontological evidence. ^{[2] [3]} In an effort to determine the causes of the “gap”, the researchers were faced with a difficulty: is this “gap” attributable to global extinction, or are we dealing with isolated extinctions of individual groups that are part of some more general process? Some theories spoke of prolonged extinction, stretching over several million years, ^[4] others - of several waves of extinctions preceding the devastating Permian-Triassic . ^{[1] [5] [6] The} Olson extinction made the subsequent Permian mass extinction even more devastating, which ultimately led to the extinction of 80% of the species existing at that time, and smaller scale extinctions occurred between large-scale extinctions.

In the 1990s and 2000s, researchers accumulated data on the biodiversity of plants, marine animals and tetrapods, and these data showed that the preceding Permian-Triassic disaster had a significant impact on life on the then Earth. For terrestrial fauna, Sahney and Benton show that even if we discard the fact that fossils that are directly related to the extinction period are rare, the fact of extinction is confirmed by the fact that in the immediately preceding and subsequent periods, the fossils are numerous - which means that the point is not in the poor preservation of the fossil record, but in the impoverishment of the biosphere, which we now call the “Olson extinction”. ^{[1] The} “gap” was finally “closed” in 2012, when confirmed that the Middle Permian fossils of terrestrial animals are well represented in the southwestern United States and the European part of Russia, and also that Olson’s the gap ”is due not to lack of data, but to extinction, which interrupted the continuity between the Early Perm and Middle Permian faunas. ^[7]

Despite the closure of the Olson gap, the fact of extinction on the border of the Kungur and Road centuries (272.95 million years ago) remained a subject of controversy for some time. A number of researchers argued that the observed lack of continuity could be explained not by extinction, but by a shift in climatic zones: the climate of the studied regions from equatorial and tropical could become temperate, and the temperate zone always (and now) is characterized by less species diversity. ^[8] However, a closer examination of the formations with four-legged fossils belonging to the Kungur and Road centuries revealed that changes in the species composition of the fauna of this period are not explained by the displacement of natural zones in the studied areas: the Early Permian faunas of temperate latitudes have more in common with the Early Permian equatorial faunas than with the Middle Permian faunas of the same temperate zone. ^[9] It also turned out that throughout Perm the greatest species diversity was characteristic of temperate rather than tropical and equatorial climates, and therefore a change in natural zones cannot explain the decline in biodiversity. ^[9]

There is no generally accepted theory about the causes of Olson’s extinction. Recent studies show that climate change could be such a cause. Kansas Permian deposits show that harsh conditions were typical for that time: a dry climate and high acidity of water, both of these factors could lead to mass extinction. ^[10] However, whether this climate change was caused by processes taking place on Earth, or whether it was amplified by any other factors, such as an impact event, is unknown.

Land

Plants

From the Middle Permian to the beginning of the Triassic, more than 60% of plant species were replaced by others. This extinction lasted approximately 23.4 million years, beginning with the Olson extinction and ending at the beginning of the Middle Triassic. ^[11] Olson extinction is the third most deadly extinction of plants in the Paleozoic; it destroyed up to 25% of the genera of plants existing then. . ^[12] Plants propagating by spores are particularly affected; seed-propagating plants, this extinction has hardly affected. ^[12]

Four-legged

Perm was a time of rapid changes that affected the then-existing four-legged; in particular, there was a sharp transition from the early faunas, in which the basal synapsids ( pelicrosaurs ) and reptiliromorphs ( diadects ) dominated , to the late faunas, in which other groups already dominated: therapsids ( deinoecephals , anomodonts , gorgonopses and tsinodonts ), some representatives of these progressive groups subsequently became the direct ancestors of mammals. ^[7] In 2008, Sahley and Benton ^[1] showed that this was not just a change of fauna (which should have been gradual), but a real extinction, which greatly damaged the ranks of the four-legged then. Most likely, this extinction took place in two stages: on the border between the Kungur and Road centuries, the edaphosaurus and ofiacodonts disappeared, due to which at the beginning of the Road age the rapid evolution of caseids and terapsids became possible, later in the same Road age the sphenacodonts also died out, and the number of caseids greatly decreased. ^[13] It seems that for the group [ [1] ] Olson's extinction was the most devastating in the Paleozoic, even more devastating than the Permian-Triassic. ^[14] Amphibians were also severely affected. ^[eight]

In December 2011, Modesto and others described fossils of the “latest” pelicosaurus, discovered in sediments of 260 million years old in South Africa ; these fossils are the first evidence that some of the pelicosaurs survived the Olson extinction. ^[15] Such taxa of animals or plants are called [ [2] ], because, having survived the catastrophe, they are the first to inhabit previously devastated lands and can take advantage of opportunities for further evolution.

Sea and Freshwater

Pisces

During the Olsonian extinction period - between the Kungur and Road centuries of Perm - the rate of fish extinction increased significantly. ^[16] However, the rate of formation of new species also increased, so overall the decrease in fish diversity was insignificant. ^[16] Using data on the variety of cartilaginous fish , Koot shows that their diversity decreased slightly and this situation persisted until the middle of the Road Age. ^[17]

The Permian-Triassic catastrophe hit the Earth too quickly - when the fauna had not yet had time to recover and recover from the Olson extinction. Estimates of the time taken to restore ecosystems vary, a number of authors claim that life on Earth finally recovered only in the Triassic, 30 million years after the Olson extinction and also after the Permian-Triassic. ^[one]

The Olson extinction contributed to a number of important events, including the emergence of therapidside , the group from which mammals subsequently evolved. A study of the newly identified primitive therapids from Road Age [ Xidagu ] ( Qilanshan Mountains , China) may shed further light on this issue. ^[18]

• io9.com: "Why did nearly all life on Earth die 250 million years ago?"
• Vancouversun.com: "Canadian researchers spearhead fossil discovery of resilient prehistoric animal." (inaccessible link)