Permian Period: The Harshest Winter of the Paleozoic

Permian

298.9–251.902 million years ago: Winter of the Paleozoic, rise and fall of therapsids

International (and Russian) scale:

298.9 mya — Cisuralian epoch: Asselian — 293.52 — Sakmarian — 290.1 — Artinskian — 283.5 — Kungurian (Kungurian, Ufimian) — 272.95 — Guadalupian (Biarmian) epoch: Roadian (Kazanian) — 268.8 — Wordian (Urzhumian) — 265.1 — (Tatarian epoch) Capitanian (Severodvinian) — 259.1 — Lopingian epoch: Wuchiapingian (Vyatkian) — 254.14 — Changhsingian — 251.902

The Permian period is the coldest period of the Paleozoic and one of the coldest in the planet«s history. The terrible climate could not help but drive evolution — it is no accident that in the Permian all prerequisites for the emergence of mammals appeared. A little more — and animals would have fully formed and taken over the planet, and intelligence could have shone hundreds of millions of years earlier.

But the Permian is also the most tragic period: at its end, almost all achievements of the Paleozoic were destroyed. This cataclysm, known as the Permian extinction, is still little known to most people, although it was the most massive in Earth«s history.

In the Permian, all continents last pressed tightly together into a single Pangaea, as if trying to keep warm. In fact, cause and effect are directly reversed here: the huge supercontinent blocked equatorial currents, leading to global cooling.

The huge size of the land led to a continental climate: clouds simply did not reach inland areas, where vast wastelands and even real deserts spread. Of course, there was no cold in the equatorial region, and coasts and mountain slopes were regularly irrigated by rain, but on average the planet was cold and dry.

At the end of the Carboniferous period, the Early Permian ice age began, lasting until the beginning of the Artinskian. During this time there were at least two glacial episodes, traces of which have been found in Australia, Brazil, Africa, Antarctica, Arabia, India, Myanmar and Malacca. Glaciers spread from Antarctica in all directions — up to 30° south latitude, i.e. to the latitude of the modern southern parts of Africa, Australia and Brazil. Temperatures were on average 4° lower than modern — seemingly very little, but Permian glaciations are second only (and not by much) to the most severe cold of the Cryogenian and Pleistocene.

Huge masses of fresh water went into glaciers, causing salinity in the ocean to rise sharply — the highest in the entire Phanerozoic. Salt concentrated, evaporated on the coasts and deposited in huge strata. Over the entire Permian period, up to 10% of the salt in the modern world ocean went into sediment! That means before the Permian, ocean salinity could have been 10% higher. Obviously, this could not but affect all oceanic life.

A small nuance

Permian salt accumulation influenced world history. Thanks to Permian glaciations, huge salt deposits formed in the Perm region, which have long been exploited by local residents. Salt was one of the economic foundations of the proto-state of Great Perm, and it is still mined today. It is no coincidence that the phrase «Permyak — salty ears» arose, originally purely abusive, but now become a «fashionable slogan.»

On the other hand, due to the withdrawal of water into glaciers, the ocean level dropped, opening up vast expanses previously flooded by shallow seas. On the freed spaces, weathering of Carboniferous coal-bearing deposits with sulfides began, leading to sulfate accumulation and, accordingly, oxygen burial.

However, ecosystem productivity decreased. Unlike the carboniferous abundance, little organic matter was buried, earlier formed carbonates gradually broke down, increasing the concentration of phosphates and carbon dioxide in the water, which in turn stimulated photosynthesis of cyanobacteria and algae and increased the amount of oxygen. Such is ecological dialectics!

Still, overall life became harder. Throughout the Permian, the diversity of marine animals only slowly declined, turning at the end into a terrible drop into the abyss. But before the cataclysm there were long 47 million years.

Changes in corals are indicative: throughout the period their diversity and size only decreased. Tabulate corals became small and often parasitic, a good example being Pseudofavosites. At the end of the period, coral structures become rare and localized in the most favorable places.

From the Kungurian of South Africa, the first reliable lancelet Palaeobranchiostoma hamatotergum is known, of a rather strange appearance: unlike its modern descendant, the Paleozoic one had an almost triangular shape due to a sharp snout, a large dorsal fin and a particularly long lower fin. The most surprising feature is a row of spines along the back from the «head» to the tip of the dorsal fin. How harsh was the Permian that even lancelets became hedgehogs!

Among fish in the Permian, cartilaginous sharks were especially successful. Perhaps the most mysterious fish of all times and peoples are Helicoprionidae. The first were moderate representatives — Early Permian Parahelicoprion from the Urals and Bolivia, and the Late Permian Sarcoprion edax from Greenland. The teeth on the front of their lower jaw — the symphysis — protruded in a convex upward arc. As is often the case with cartilaginous fish, the general appearance and even body dimensions are purely conjectural. Some Parahelicoprion probably reached as much as 12 m in length, Sarcoprion was half as modest — «only» 6 m. Thus, these fish have record sizes for Paleozoic animals.

An exotic development of such monsters were the Early-Middle Permian representatives of Helicoprion, of which the first described and best known is H. bessonovi. In this fish, the teeth curled into a rather tight spiral of two or three full turns, with teeth small in the center and increasing towards the outer end; a single spiral could contain up to 190 teeth.

Judging by various subtleties, growth began precisely from the center of the spiral, but then it is difficult to understand how the whole structure was attached — did the jaw curl like a roll or was there some cartilaginous axis? The wear on the teeth was minimal, so it is generally unclear — why so many teeth if they were hardly used?

According to the most modern and detailed reconstructions, the tooth spiral of Helicoprion lay at the bottom of the oral cavity and was used to cut the tentacles of cephalopods. Given the structure of related sharks, it is reasonable to assume that Helicoprion«s mouth may have also contained other types of teeth used to crush shells and carapaces. The largest spirals — up to 56 cm — could belong to fish 7.5 m, and according to other estimates, 9–12 m in length.

Correcting errors

Paleoichthyologists have proposed all sorts of hypotheses regarding the location and use of the tooth spirals: that they curved upward on the snout, downward, forward or upward on the lower jaw symphysis, in the pharynx, in a special capsule at the bottom of the oral cavity, on the dorsal or even caudal fin, that one fish had one spiral or a pair, that the entire structure could move and straighten, that old teeth were the largest or the smallest.

However, comparing helicoprionids with other related cartilaginous fish, more than half of the options can be safely excluded. So far, besides the spirals themselves, there is only one tomographic reconstruction of the jaw cartilages. Sooner or later a beautiful imprint of an entire head will be found, and some paleoichthyologists will triumph: «I told you!», while others will modestly keep quiet.

Other unusual Permian sharks — Xenacanthida (or Xenacanthiformes), for example Orthacanthus and Xenacanthus. These were not small fish — from one meter to three or even four, especially considering they lived in freshwater bodies. These elongated sharks had a huge spine sticking out on the back of the neck, which in ancestors was located at the base of the dorsal fin but over time shifted to the head; the dorsal fin itself turned into a long low lobe.

The upper lobe of the caudal fin became a long tapering end of the body, and the lower lobe shifted far forward, effectively becoming a second anal fin. The teeth had a strange V-shape, apparently designed for crushing the shells of crayfish and paleoniscids. In fact, representatives of both mentioned genera appeared at the end of the Devonian and went extinct only at the end of the Triassic — an amazing stability, given the many events that occurred during this time.

At the beginning of the Permian (but, characteristically, not at the boundary of the periods), the last acanthodians and lobe-finned rhipidistians went extinct. In Permian deposits, a fossil burrow of the lungfish Gnathorhiza has been found: a concretion shaped like either a club with a groove or a very thick spoon, formed when the fish burrowed into deep mud and then curled up there for sleep during the dry season, only the sleep turned out to be eternal.

At the end of the Permian, the bony ganoid Holostei split off from the palaeoniscids, already very similar to full-fledged teleosts and sometimes combined with them into one group Neopterygii. The oldest amiid Acenthrophorus varians from the Late Permian of England looked rather dull, as befits the great ancestor of a huge group that arose from it.

Correcting errors

In scientific terminology, great liberties are sometimes allowed, and sometimes a few letters completely change the meaning. One of the most common confusions is with the concepts of «bony fish» and «teleost fish.» Bony fish Osteichthyes are all those that have bone tissue anywhere in their internal skeleton; while most of it can easily be cartilaginous, as in chondrosteans and lobe-finned fish.

Teleosts (Teleostei) are only those that are completely bony, with the entire skeleton ossified. Clearly, there are many other important features. Bony ganoids fall between the first and second: their skeleton ossifies, so sometimes they are combined with true teleosts into one group Neopterygii, but their scales are ganoid, and there is much archaic in their structure.

Modern bony ganoids include only gars Lepisosteus and the bowfin Amia calva, but in the Mesozoic this was a very rich group. Gars are not called alligator gars for nothing — their toothy snout really resembles a crocodile«s.

A favorite pastime of American fishermen is to catch a couple of gars, put them on the shore, step back about two meters, and take a photo in a pompous pose with a large depth of field so that it seems that the brave fisherman has caught some terrifying monsters. However, some gars grow up to four meters in length without any special effects. Small gars are sometimes kept in aquariums, where they delight the eye with their Paleozoic appearance.

The terrestrial floras and faunas of the Permian were surprisingly uniform from the Polar Urals to South Africa, because the unity of Pangaea guaranteed ease of migration.

A small nuance

By the way, it was the distribution of identical traces of Carboniferous and Permian glaciations on now distant continents, as well as the similarity of Gondwana faunas in the Permian and Triassic, that prompted A. Wegener to think about continental drift.

However, in different areas ecosystems still did not look identical. In the last refuges of the humid tropics of the Euramerican region, tree-like horsetails and lycopsids shrank. Late Calamites and Sigillaria, as well as less known Paichoia and Signacularia, are much more modest than their majestic ancestors. The swamps, from which the columns of lycopsids protruded, covered with floating mats of water mosses, liverworts, algae and cyanobacteria, gradually dried up, and their places were taken by fern and coniferous forests.

Extremely common plants here were numerous species of the tree fern Asterotheca. The cold northern regions of the Cis-Urals and Siberia were covered with endless gymnosperm cordaitian taiga. Siberia is Siberia, even proximity to the equator did not help it, taiga and cold — 300 million years of stability! Permian cordaites had very small foliage, an example being the numerous species of the «leaf genus» Crassinervia.

The cold southern regions, which still included the merged South America, Africa, India, Antarctica and Australia, were overgrown with forests of primitive gymnosperms Glossopteridales (again Glossopteris) and Ginkgoopsida.

The first reliable ginkgos — French Trichopitys heteromorpha and Sphenobaiera — appeared in the early Permian. They had narrow dichotomously branching leaves, more like needles, densely covering the shoots. Another probable relative of ginkgo is the Argentine Polyspermophyllum sergii, whose leaves resembled snake tongues; undoubtedly local residents would have called it that if it had survived to modern times.

At the end of the Permian, both in the north and south, new forests appeared, composed of spruce-like Voltzia, together with several relatives forming the group Voltziales. These were drought-tolerant trees, whose leaves turned into scale-like needles, densely covering the branches; however, the tips of the branches were decorated with long needles like those of pines.

The change of flora led to a change in arthropod fauna. However, Permian crustaceans Triops and Lepidurus at the generic level already did not differ from modern ones; in principle, they can be mentioned in every subsequent period, using the same words — for them, Groundhog Day came long ago and hopelessly.

Archaic paleopterous insects did not disappear. From the Carboniferous to the Permian, the paleodictyopterans Goldenbergia and Dunbaria, which fed on cordaite pollen, smoothly transitioned. Mayflies, such as Misthodotes, did well, and their larvae are also known — Kukalova americana.

No matter how famous the Carboniferous protodonates were for their size, the largest insect in the entire history of the planet was the Early Permian Meganeuropsis permiana from Kansas and Oklahoma: its wingspan reached 71 cm! Other large Permian meganeurae are Tupus and Arctotypus.

In the Permian, the order Plecoptera (stoneflies) arose — relatives of cockroaches, whose larvae again switched to an aquatic lifestyle. The earliest stonefly Perlopsis filicornis from the Kungurian of the Cis-Urals is known both as an adult and as a larva; later a great many of its relatives appeared.

The abundance of plant debris was also fed upon by the first psocids (Psocoptera, or Copeognatha; e.g., Permopsocus congener) — distant and still vegetarian ancestors of lice.

At the beginning of the Permian, ancestors of cicadas and bugs appeared — for example, Archescytina, Maueria, and Permopsylla. It is hard to name the very first cicada; they appear suddenly and in a large company. The mere existence of sap-sucking insects is extremely indicative: therefore, plants had become succulent enough that some benefit could be sucked out of them.