Name Diameter [kilometres] Age [Million years] Geographical location Coordinates
Bedout ~ 200 km 250.1 ± 4.5 Ma Indian Ocean (Northwestern Australian coast)  
East Clearwater Lake 20 km 290 ± 20 Ma Canada, Quebec N56º 05', W74º 07'
West Clearwater Lake 32 km 290 ± 20 Ma Canada, Quebec N56º 13', W74º 30'
Kentland 13 km <300 Ma USA, Indiana N40º 45', W87º 24'
Ternovka 12 km 330 Ma Ukraine, Dnepropetrovsk District N48º 01', E33º 05'
Charlevoix 54 km 342 ± 15 Ma Canada, Quebeg N47º 32', W70º 18'

 

Note:

Although not confirmed, there seems to be some evidence of the another impact at the Permian/Triassic boundary.

Permo-Triassic extinction is the largest known in the history of life. According to some of my sources, as much 95 procents of all organisms died out in this extinction. See my old Seminal essey below

 

Seminar of Ecological Palaeontology
Department of Geology
Section of Geology and Palaeontology
University of Helsinki
12.02.1999

Evolution of the Permo-Triassic land ecosystems.

Mikko Haaramo

 

I. Evolution of Permian ecosystems:

Permian (290 - 251 MYBP) is the last age of the Palaeozoic era. During Permian the Mesozoic ecosystems started to appear.

In a general way, the Early Permian ecosystems appear very similar to the Late Carboniferous ecosystems. During the Early Permian, the flora was still mainly composed of "primitive" Carboniferous-type plants like mosses, lycophytes, ferns, tree-ferns, horsetails and seed-ferns. Early Permian climate seems quite similar to Late Carboniferous climate, with a slight tendency towards a warmer climate. The plant-fossils seem to indicate that throughout the Permian the climate was generally similar to a modern climate; lower latitudes being warm and wet, higher latitudes mild to cold, up to glacier-level.

At Early Permian, the main land-vertebrates were temnospondyls, which were at that time already archaic, and newly evolved basal synapsid amniotes (so called "pelycosaurs"). Pelycosaurs make about 70% of known amniote fauna. Among these main forms were small lizard-like primitive diapsid and anapsid amniotes. The land-invertebrate fauna appears to be quite typical, composed of insects, millipeds, arachides, etc.

The best-known land-ecosystem from Early Permian has been found from Texas, USA. At Early Permian times this area seems to have been in the tropical pelt, around 10° northern latitude. At this location the main carnivores are various pelycosaurs, like Dimetrodon. The herbivores were primitive caseasaurid and edaphosaurid pelycosaurs as well as advanced amniotamorph Diadectes. The herbivore fauna appears to be continuous from the Late Carboniferous. Some elements of this pelycosaur-dominated fauna has been found from other places in America and Europe, as well as from Northern Africa and Russia. These finds are at best very fragmentary. However, it appears that the Texasian fauna is typical for Early Permian times, and it shows that during that time pelycosaurs were essentially a tropical group, comparable to modern poikilotherm amniotes.

Approaching the Late Permian the land animal faunas appear to have evolved towards dry-resistance. Some of the largest arid deposits in the history of Earth are known from Late Permian sediments of Europe. The widespread aridity is also known from North American and Southern Gondwanan sediments.

At the beginning of Late Permian, the pelycosaurs are replaced by their evolutionary successors, the therapsids. They undergo an adaptive radiation which gave birth to many new morpho-types, including herbivorous dinocephalians and dicynodonts, as well as carnivorous gorgonopsians and theriodonts, for example cynodonts. Most anapsid- and diapsid amniotes remained small, with one notable exemption. The pareiasaurs, which evolved from primitive anapsids in competition against herbivorous therapsids. Some of the Late Permian land-vertebrates were quite large, the largest gorgonopsid, Inostrancevia was over 4 metres long, and one of the largest herbivores, pareiasaur Scutosaurus, has been estimated to weigh appr. 1.5 metric tons.

In contrast to Early Permian, these animals have been found from areas where climate was temperate. Some areas are even though to have been seasonally cold, comparable to present day Central Europe. The main difference between therapsids and pelycosaurs appears to have been the therapsid ability to stand a harsher environment, where the pelycosaurs couldn't compete with them.

Cycads and gingko's started to appear in early Late Permian flora. Their presence makes Late Permian ecosystems appear more Triassic. The most typical of the Permian plant-life seems to be the high-latitude plants, like Cordaites from Eastern Siberia, and the Glossopteritales seed-ferns from Gondwanaland. Both groups appear similar to modern temperate trees in that they seasonally shed their leaves. Among the Late Permian flora are also Voltziales, from which the modern conifers are thought to have evolved.

II. The Permo-Triassic mass-extinction event:

The Permo-Triassic mass-extinction (the P/T event) is undisputedly the greatest single mass-extinction event in the history of the Earth. Professor J. J. Sepkoski and his collages have estimated that over 50% of all animal families went extinct during this event. And its possible that over 95% of all marine animal species died out. The land ecosystems appear to be similarly devastated, with about 70% of all land animals disappearing.

This massive extinction laid waste to the well-established Palaeozoic ecosystems and animal-groups. At same time it extinguished many old evolution-paths, like trilobites, that went well back to Cambrian.

The effects of the P/T event are now fairly well known, but unlike the End-Cretaceous extinction (the K/T event), the causes of the P/T event are still largely unknown. Some scientists say that there was a sudden cold spell during Late Permian, while others say that the climate warmed suddenly. Several causes are supposed to explain the marine extinctions. Currently the best candidate is the reduction of marine coastal and shelf-areas caused by the tectonic events of Late Permian, which has pushed the continents together. There appears also to have been a relatively fast drop of the sea level (some 90 metres), but thinking about modern times the fast changes in sea-level have seemingly no effect to marine invertebrates, so the cause of marine extinction's have to be something other than this. Also, the marine waters of Late Permian appears to have been stratified, causing probable anoxic conditions at deeper sea levels. Rapid sea-level changes could have dried the low level shelf-areas, then flooded them with poisonous water with low levels of oxygen and high levels of hydrogensulfide (HS) and other toxic compounds.

When causes of terrestrial extinctions have been sought, nothing as simple as the K/T -event's huge extra-terrestrial visitation hasn't been found. What is known is that one of the greatest plateau-basalt (i.e. traps) eruptions happened in Eastern Siberia. According to scientists who have studied this eruption, it covers an present area of more than 2.5 million sq. kilometres (2 500 000 km2), and has an estimated original volume of 2-3 million cubic kilometres (2 000 000 - 3 000 000 km3).

Effects of an eruption of this size, happening in a relatively short time (appr. some 1 million years), are, needlessly to say, devastating. The local effects from volcanic gases, ash, and flowing lava are probably enough to kill most of the local animal- and plant-life. The far-reaching effects of the eruption are similar to a large impact, but spread out in time and thus having a much longer effect. The eruption would have produced huge a mounts of carbon dioxide (CO2), carbon monooxide (CO), hydrogen sulfite (HS), different CFC-compounds and other volcanic gases. The sulphur- and CFC-compounds would as aerosols have risen to the stratosphere, effecting both sunlight and the ozone layer.

In short, the effects of the eruption were similar to a typical nuclear or impact winter event, but spread out over much longer period of time. This longevity caused by the eruption winter-event would have had a much greater effect on plant-life than a relatively short nuclear or impact winter-event. And, indeed, unlike the K/T -event, during the P/T -event there is a noticeable extinction of plant-life on all continents. The typical Late Permian temperate forest plants like glossopterids and cordaites went extinct. The tropical forests were also devastated, as most primitive ferns, treeferns and tree-lycopods died out. It is unknown why the primitive conifers managed to survive as well as they did.

The land-faunas are similarly decimated, as almost all Late Permian therapsids died out, and only 3 - 5 lineages survive. The anapsids are hit hard by extinction, leaving only the ancestors of modern turtles. How diapsids suffered is not at present known, as they were a rare element in Late Permian ecosystems. The amphibians are almost extinguished, and it is estimated that as few as 5 - 6 lineages of amphibians survive.

III. Evolution of Triassic ecosystems:

After the Permo-Triassic mass extinction, the first Early Triassic land ecosystems appear. They are truly bizarre, as their monotypic flora and fauna in many ways look like modern monotypic cultivation areas due to most of the fauna and flora being extinguished.

The most common Early Triassic herbivore is the advanced dicynodont Lystrosaurus, which formed huge, monotypic herds. Their main predators were early cynodonts, like Procynosuchus, some of which grow to a considerable size. Among the predators were the first primitive archosauromorphs, like the South African Proterosuchus, and the Russian Chasmatosaurus (which may be synonym taxons).

Remaining therapsids react rapidly to vacant niches, and start to diversify. The remaining dicynodonts evolve rapidly, and by the Middle Triassic some of them became fairly large animals, comparable in size to largest pareiasaurs. The cynodonts also evolve rapidly and they too grow in size, so that by Middle Triassic we have creatures like Cynognathus, similar in size to a modern lion. The morphotypic evolution of therapsids appear to be much poorer. Most Middle Triassic therapsids, if not all, appear only as variations of the same Early Triassic theme, with no new innovations in morphology or lifestyle.

The newly evolved archosauromorphs also diversify, but their basic body plans stays similar to Early Triassic forms. By the early Middle Triassic, however, the true archosaurs appear for the first time and start a rapid evolution burst evolving many new forms and morphotypes. This onslaught on the old kingdoms of therapsids starts slowly, but the old therapsid communities are then displaced with ever increasing speed, so that by early Late Triassic the therapsid diversity has declined seriously. Gone are all dicynodonts and large cynodonts. Remaining therapsids are medium to small-sized advanced cynodonts, among which the mammals start their evolutionary path.

The flora of Early Triassic is similary affected as the animals. The most well established land plants of Late Permian are gone, and the remaining flora is starting to fill up the gaps. In sediments this extinction of the flora appear as an almost 20 million year gap in the peat forming plants. Thus there is no Early Triassic coal to be found anywhere. By the Middle Triassic plant-life has recovered slightly, so that small deposits of goal has been found.

By Late Triassic, some 30 million years after the “Great Dying”, the animal and plant life appear to have recovered from the extinctions. The diversity of life has restored itself. Among the Late Triassic faunas are the newly evolved dinosaurs and pterosaurs, gigantic crocodile-like rauisuchids, primitive true crocodiles, phytosaur-false crocodiles and plant-eating aetosaurs. Among the archosaurian forms are rynchosaurs and trilophosaurs. Scurrying and slithering among the undergrowth are the first primitive lizards, their sphenodontian cousins, various small amphibians, and of course the remaining members of the once proud therapsids; the mammals. The seas are teeming with reptilian forms like ichthyosaurs, nothosaurs, placodonts, turtles and plesiosaurs.

 

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