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Author(s) of the publication: Sergei NAUGOLNYKH

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by Sergei NAUGOLNYKH, Dr. Sc. (Geol. & Mineral.), RAS Geological Institute

What was the plant world of the Urals a quarter of a billion years ago? Today one can discuss this not only in hypothetical terms. The real picture-far from complete-of significant changes of landscape which took place there in the Permian period - the last in the Paleozoic era-is being gradually restored by samples of ancient flora discovered by scientists in that region.

CONIFEROUS FORESTS OF THE PIEDMONT OF PALEOURALS

Distinct climatic zonality which existed at that time on a global scale promoted the differentiation of vegetation. It differed substantially in every natural zone of the Northern Hemisphere-from the equatorial and tropical to moderate and cold ones. Today we want to discuss only the flora of the western slope of Paleourals which stretched along the eastern cost of a sea gulf, that ceased to exist in the middle of the Permian, and the changes which occurred there over 40 mn years. There are reasons to believe that in the history of the plant world of the Late Paleozoic there were no fewer dramatic periods than in the history of the animal world.

In the Carboniferous period and early in the Permian, in connection with orogenesis (process of formation of mountains) mountain chains no smaller than the Alps or the Caucasus of our time, rose in many regions of our planet. Now, after 250 mn years, they have crumbled down completely or in part. That epoch, called Hertzinian or Variscian, is when the Urals was born.

Pages. 103

Early Permian shenophytes and ferns. In the foreground - sphenophyte Equisetinostachys Rasskasova. In the background to the right - Marattialean fern.

Leaves and generative organs of coniferophytes, belonging to the order of Vojnovskyales. To the right - stems of Phyllotheca Brongniart.

Which plants flourished on the slopes of the Paleourals in the very beginning of the Permian - Asselian and Sakmarian - remains unknown. Only a few years ago scientists discovered some seeds and mineralized bits of wood in terrigenic deposits (fragments of rock washed off the shores, hill and mountain slopes), containing bits of shells of extinct marine cephalopods, bits of seeds and mineralized wood. Researchers also discovered some better preserved fragments of plants, like shoots with needle-shaped leaves, attached in spirals. Paleobotanist Vera Vladimirovich from St. Petersburg identified them as belonging to primitive conifers - Walchia schneiderii Zeiller and Ernestiodendron sp., and her opinion was supported by other specialists in Paleozoic floras.

The two aforesaid genera are now regarded as the most primitive conifers located at the base of a group which includes, according to present-day systematics, several families which moved far apart by their morphological features in the process of evolution. Representatives of Walchia and Ernestiodendron have been studied in detail on the basis of Western European materials from the Lower Permian. It has been possible to demonstrate the belonging of their organs (cones or strobils*, seeds, pollen, leafy shoots) to the same botanical species. Thanks to finds of nearly whole trees with branches, preserved attached to the trunks (in some cases branches carried strobils) it has been possible to reconstruct the plant itself.

Walchian conifers are known from different regions of the Earth (North America, northern part of Africa, Europe, northern part of China etc.). But if you put all these locations on a paleogeographical map, you will see that all of them gravitate to a rather narrow belt along the paleoequator and partially covering the tropical and subtropical zones. Thus, as different from most contemporary members of this group, ancient conifers were rather thermophilic ("heat-loving") and their needle leaves were adapted not to seasonal colds, but to a dry climate which formed in the low latitudes at the beginning of the Permian.

THICKETS AT SALTY LAGOON

By the end of the Early Permian epoch, in the Artinskian (some 277 - 273 mn years ago) and especially Kungurian stages (273 - 269 mn years ago) the sea gulf which occupied the pre-Urals bend, became shallower, which was caused in part by it being filled with marine sediments and sediments washed off from the Urals. The process was promoted by global aridization of the climate and gradual tectonic elevation of the whole region.

* Strobils - reproductive organs characteristic of several higher plant groups (horsetails, conifers etc.); modified shortened snoots carrying specialized leaves bearing sporangia or seeds. - Ed.

Pages. 104

Lycopsids Viatcheslavia vorcutensis Zalessky. A - phylloid; B - general habit of the plant; C - sporophyll; D, E - microspores. Length of scale 1 cm (A, C), 10 cm (B), 20 pan (D, E).

Ufimian vegetation of the Late-Permian epoch. Monodominant communities of Viatcheslavia vorcutensis Zalessky. Up left - giant dragonfly Arctotypus.

As a result, in the Kungurian the gulf, which contained plenty of marine organisms, turned into a salty lagoon stretching all along the Urals. Located in its northern part were giant deposits of salts and in the southern - thick layers of gypsum and anhydrite.

An area located between the gulf and the mountain system was a relatively narrow-some tens of kilometers wide. This narrow but long zone received water from rivers running down from the western slope of the Paleourals and from seasonal rains. The flora which existed in this zone was relatively isolated, highly endemic with plant migrants entering the zone from the south and northeast. So it was in the piedmont zone that there developed vegetation of amazing plenty and diversity. There predominated sphenophytes (with almost direct descendents of present-day horsetails), lycopsids, pteridosperms or "seed-ferns" including relict forms preserved from the Carboniferous period (order Trigonocarpales: genus Demetrocarpus Naug.) and newly evolved forms (order Peltaspermales: genera Peltaspermum Harris, Rhachiphyllum Kerp (al. Callipteris Brongniart), Psygmophyllum Schimper emend. Saporta) which phylogenetically linked with younger groups which dominated in Mesozoic floras. In the Kungurian flora there were many conifers - direct descendents of Walchiaceae of the beginning of the Permian period (order Coniferales (=Pinales); family Walchiaceae; genera Kungurodendrom S.Meyen, Bardella Zalessky, Bardospermum S.Meyen). .Another group of gymnosperms, little studied so far, are Vojnovskiaceae. Preserved to our days is a living fossil - Ginkgo biloba L. and there were several closely related plants in the Kungurian flora. And now more details about some of these plants.

LYCOPODS OF THE EARLY PERMIAN EPOCH

In the late 1980's during fieldwork at one of the most famous sites of Kungurian flora located on the bank of the Chekarda River (basin of the Sylva River, Perm Region) I happened to find a surprising fossil plant. It was a long narrow leaf with

Pages. 105

Leaf of fern Pecopteris sp. (1): present-day fern (2); part of leaf of Peltaspermum retensorium (Zalessky) Naugolnykh et Kerp (3); phylloid of Sadovnikovia belemnoides Naugolnykh (4). Kungurian (1, 3, 4). Magnification x3 (1), x0.2 (2), x2 (3, 4).

the single conducting strand and an expansion at the base which turned out to be sporangium. At the most narrow part of the leaf there were two dark lines with stomata - microscopic "holes" in the leaf epidermis, regulating gas exchange. The edge of the leaf was more dense which is typical of many fossil lycopods.

This uncommon fossil was a sporophyll of an ancient lycopsid plant which I described as the new genus and species Sadovnikovia belemnoides Naug. (named in honor of the Moscow paleobotanist G. Sadovnikov). It was surprising but it looked very much like present-day Isoetes L. and its close relative recently discovered in the Andes Stylites). Before this find the chain of phylogenetic predecessors of Isoetes was more or less confidently traced to the early Cretaceous from where are known lycopsid Nathorstiana arborea Magdefrau. The Nathorstiana was several centimeters high (much higher than the present-day Isoetes). The sporophylls of these two are practically identical.

In the Triassic (the earliest period of the Mesozoic, some 235 - 185 mn years ago) are known rather many forms which belonged to the family of Pleuromeiaceae. These plants had similar sporophylls in their general morphology. Sadovnikovia shows that the appearance of the Pleuromeiaceae, predecessors of present-day Isoetes, could be traced considerably deeper into the past - into the Early Permian epoch. At the same time the surprising similarity of Sadovnikovia and modern quillwort makes it possible to assume that the most ancient Isoetaceae could have diverged from the Pleuromeiaceae already in the Permian.

Pages. 106

Fossil sphenophytes from the Permian deposits (2 - 4) and present-day horsetail (1). 1 - Equisetum sylvaticum L., forest horsetail; 2 - part of a big trunk of Calamites gigas Brongniart; 3 - part of a shoot with leaf verticils Phyllotheca sp.; 4 - lower part of shoot Paracalamites decoratus (Eichwald) Zalessky. Kungurian (4), Kazanian (2, 3). Magnification x1 (1, 3), x0.5 (2), x1.5 (4).

ANCIENT ANCESTORS OF HORSETAILS

Another plant which grew along the banks of the Kungurian lagoons was Equisetinostachys peremensis (Zal.) Naug. Its reproductive organs in general looked like those of the present-day horsetail, but were different from it in such morphological feature: they consisted not of a single cone, or strobil on top of a sprout, but of several fertile zones which produced a complex verticils of sporophylls. The fertile zones were separated from each other by verticils of sterile leaves.

Another sphenophyte - Paracalamitina striata (Schmalh.) Zal. emend. Naug. related to the Kungurian equisetinostachyans, was described from the younger deposits of the Cis-Urals. Its reproductive organs still remained the activity of the terminal meristems*: on tops of the "quazistrobils" was preserved a tuft of sterile leaves, but the number of fertile zones reduced to one, and in very rare cases to two.

It has been a quarter of a billion years since thickets of these plants covered the banks of the Kungur lagoons, but even now we can see their distant descendants striving for shady and humid sites in our forests. One should look at them with respect: many of the contemporaries of their distant predecessors have long disappeared, and the horsetails, amazingly modest, but also attractive, are still seen around streams and forest rivers with dry crackling of rubbing branches, as long time ago in the Permian period.

CRISIS COMMUNITIES OF VIATCHESLAVIAS

It has long been noticed that in places where natural vegetation was damaged due to some reason (like fire) the ground plant cover starts to

* Terminal meristems - plant tissue which can produce new cells during whole life. Meristems help the formation of new organs-leaves, roots, flowers. - Ed.

Pages. 107

Fossil gymnosperms from the Lower Permian deposits. 1 - leaf of Peltaspermum retensorium (Zalessky) Naugolnykh et Kerp; 2 - part of leafy shoot Walchia appressa Zalessky; 3 - seed Samaropsis (?) complanata Naugolnykh; 4 - basal part of leaf of Psygmophyllum cuneifolium (Kutorga) Schimper. Kungurian (1 - 4). Magnification x2 (1), x2.5 (2),x4 (3), x3 (4).

be dominated by a single, often rather primitive species which makes the best use of its physiological tolerance for the colonization of the new space.

The rich vegetation of the Kungurian, which we have spoken about, suddenly disappeared in the end of the Early Permian and was replaced with the plant community with dominating Pleuromeia - like lycopsids belonging to the genus Viatcheslavia. Its fossil remains (assigned to species Viatcheslavia vorcutensis Zal.) occur, often in large number in clay and marie rocks of the Solikamskian Horizon (formed in the first half of the Ufimian age), located on the Lower Permian sediments in the Cis-Urals, from the Belaya river in Bashkirya to the rivers of Vishera and Kolva in the Perm Region and even the Pechora Coal Basin. And what is typical: apart from Viatcheslabia and rare mosses one can find nothing there as a rule.

Viatcheslavia is an arborescent lycopsid plant with long linear leaves, located spirally on a straight trunk without branches.

One can easily see on the preserved fragments: leaf cushions to which phylloids and sporophylls were attached and which formed repeated zones of close or rarified location of leaf and/or sporophyll scar/cushions. I am inclined to explain this phenomenon by changing growth dynamics depending on time of the year: formation of zones of approach of leaf cushions indicates retardation of plant growth, and the other way round. Linked with seasonal climate changes must have been generative cycles: reproductive organs began to form only in the favorable, more humid season.

The fact that Viatcheslavia plants produce mass monodominant burials within a broad belt of Solikamskian sediments and are typical of different faces-from coastal marine to alluvial-shows with confidence that the Viatcheslavia lycopsids predominated at that time. The micro-spores of the same Viatcheslavia are dominating in spores-pollen assemblages.

In my opinion the replacement of the Kungurian vegetation with Solikamskian one (with predominated Viatcheslavia) was the result of

Pages. 108

Conifers belonging to Walchiaceae family from the Lower Permian deposits. 1 - Tylodendron speciosum Weiss (without bark), 2 - Walchia bardaeana Zalessky; 3 - Bardospermum rigidum S.Meyen; 4 - Walchia appressa Zalessky, leaf cuticle. Kungurian (1 - 4). Magnification x3 (1), x2.3 (2), x2.5 (3), x100 (4).

Pages. 109

Gymnosperms from the Lower Permian (2, 4) and Upper Permian (1, 3) sediments. 1, 2 - Tylodendron speciosum Weiss, shoots of conifers from copper sandstones; 2 - Scirostrobus pterocerum (Naugolnykh) Ooweld et Naugolnykh, seed-bearing organ of gymnosperms supposedly belonging to the order Vojnovskyales; 4 - Entsovia inornata Gluchova, cuticle. Kungurian (2, 4), Kazanian (1, 3) Magnification x1.5 (1), x2 (2), x0.9 (3), x70 (4).

a local or regional ecological crisis, when vast numbers of taxa perished and only few were able to survive in refugiums, i.e. places were relict forms were preserved. Most of the plants were replaced with much more primitive ones then gymnosperms which dominated in the Kungurian flora. Viatcheslavians were able to benefit by their physiological advantages caused by high ecological tolerance, common to plants with a relatively simple organization, thanks to which their pioneer communities spread out for many thousands of square kilometers.

It is difficult to say with confidence what actually happened in the Cis-Urals on the border of the Early and Late Permian. I think the destruction of the Kungurian flora was caused by some climatic event, most likely by a new phase of aridization of the climate.

Phylogenetic descendants of Viatcheslavia acted time and again as ecological pioneers whose appearance marked dramatic episodes in the history of the Earth. That was the situation on the boder of the Permian and the Triassic when during a biospheric crisis there was a global extinction of terrestrial and marine organisms, when Pleuromeia communities spread out across the planet.

FLORA OF COPPER SANDSTONES

Monotonic communities of Viatcheslavia were replaced with vegetation of a new type by the second half of the Ufimian of the Late Permian. The main localities of that younger flora are characteristic of copper sandstones* which are especially common in Bashkirya and Perm Cis-Urals which accounts for the name of the flora.

The presence of remains of ancient plants and animals in these deposits was known even to people of the Bronze Age-several thousand years ago. Images of very real bears and elks

* Copper sandstones - sandstones containing large amount of minerals of copper. - Ed.

Pages. 110

Plant remains from the copper sandstones. 1 - Psygmophyllum expansum (Brongniart) Schimper; 2 - Psygmophyllum sp.; 3 - Rhachiphyllum (al. Callipteris) wangenheimii (Fischer) Naugolnykh. Kazanian (1 - 4). Magnification x1 (1 - 4).

located next to some unusual images of what we call "pangolins" can be seen on ancient buckles and decorations of ritual knives and axes. It is very likely that these images were prompted by finds of skeletons and skulls in copper mines. They must have belonged to the long extinct labyrinthodonts (amphibians) and dinocephals (animal-like reptiles). The ancient miners must have also seen fossil leaves, and petrified woods, mineralized by copper oxides. The first fossil plants from copper sandstone deposits were scientifically recorded in the beginning of the 19th century by a Russian geologist, Major Wangenheim von Kwalen. They were described at about the same time by the pioneers of Russian paleontology G. Fisher von Waldheim, E. Eichwald (Corresponding Member of the St. Petersburg Academy) and Prof. Stepan Kutorga.

The geological age of the localities of these plants is not always the same. It varies from the Late Ufimian (sections near the present-day town of Perm) to the Kazanian ones (Bashkirian Cis-Urals, deposits near the town of Belebey) and even, supposedly, of the Early Tatarian (some 262 - 257 mn years ago; Kargalinsk copper mines in the Orenburg area). The taxonomic composition of the copper sandstones floristic assemblages, despite a considerable difference of their age, have much in common and can be regarded as evidence of a common stage in the development of Permian vegetation of the Cis-Urals. Present in the flora of copper sandstones were sphenophytes

Pages. 111

belonging to several orders: Equisetales, family Tchernoviaceae (Ural representatives of genera Paracalamites and Phyllotheca) and Calamo-stachyales (Catamites gigas Brongn. - species preserved in the Permian period since the Carboniferous), and also ferns Pecopteris anthriscifolia (Goeppert) Zalessky, pteridosperms Rhachiphyllum (al. Callipteris) wangenheimii (Fischer) Naug., conifers Tylodendron speciosum Weiss, ginkophytes Kerpia belebeica Naug., Baiera cf. gigas Schmalhausen.

It is most likely that vegetation of the period of accumulation of rocks, which turned into copper sandstones after millions of years, was not one community, but several plant associations replacing one another with growing distances from temporary or permanent lakes and rivers. Growing in humid and shady ecozones were sphenophytes, at higher sites-on drained slopes, there was an association of pteridosperms, and further on watershed piedmonts-association of conifers resistant to dry weather conditions.

TIME OF PURSONGIAS

The flora of copper sandstones appeared in the second half of the Ufimian and flourished during the Kazanian. It continued to exist in the first half of the Tatarian (some 262 - 257 mn years ago). But the climate of the Cis-Urals was changing, slowly, but constantly, becoming more dry. Wet seasons with infrequent, but abundant rains, became shorter. Thick layers of red-colored clastic rocks began to form on the vast expanses of the piedmont plains with its internal-drainage lakes and temporary water discharges. Carbonate soil carapaces were produced, and paleotakyrs - clay surfaces broken up into cracks into polygonal plates were common to Permian plains.

In this situation higher plants had to rapidly adapt themselves to the new climate. The changes were especially felt by peltaspermaceous pteridosperms. Typical representatives of this plant group from cuprous sandstones had large pinnate leaves. But in the conditions of the semi-arid climate they evaporated too much water. Therefore there appeared new species of peltasperms with a small and simple leaves. Morphological changes of big pinnate leaves into smaller ones could occur in two ways. In the first case tri - and di-pinnate leaves were reduced, first to simply pinnate ones and then to simple lanceolate leaves. In the second case last order segments of pinnate leaves became separate from the others and turned into independently functioning simple small leaves. And the rachis of a pinnate leaf turned into monopodially branching shoot. Both approaches of reduction of photo-synthesizing organs are known in present-day xerophytes, i.e. plants adapted to dry conditions.

All these evolutionary changes led to the appearance and broad propagation in the second half of the Tartarian of a new type of peltasperms with simple lanceolate leaves. They were described in 1934 by the outstanding paleobotanist, Corresponding Member of the USSR Academy of Sciences, Mikhail Zalessky under the generic name Pursongia Zalessky. Specimens of Pursongia amalitzkii Zal. were found at the beginning of the 20th century by an expedition of the paleontologist Vladimir Amalitsky together with the remains of amphibians and reptiles of the Permian near the town of Kotlas on the Severnaya Dvina. They are being kept to this day in the RAS Paleontological Museum (Moscow). In 1969 the leaves, morphologically identical with Pursongia from the Tartarian sediments of the Urals, were described by geologist and paleobotanist Sergei Meyen as a new genus Tatarina S.Meyen. It was later proved by him that to plants with Pursongia leaves belonged the seed-bearing organs of Peltaspermum- type.

Peltaspermaceous pteridosperms with leaves of the Pursongia-type spread out rather widely across the Eurasian continent. Their remains were found even in Siberia and northern regions of China. Judging by these finds, Pursongia plants were shrubs up to two meters high which produce thickets around lakes and rivers. These sites were inhabited by many animals of the Late Permian. The herbivores must have been consuming the leaves and generative organs of Pursongia. In addition to Pursongia, the list of plants in the second half of the Tartarian contained many others such as Acanthopteridium spinimarginale Naug. et. Aref. found in the Upper Permian rocks outcropping along the banks of the Sukhona River. It had small and simple leaves with well developed edge thorns and other details typical of xerophytic plants.

But the history of the Permian plant kingdom did not end with the time of Pursongia. In younger sediments one can find remains of other plants which existed during latest Permian on the territory of the Russian platform. But their studies are only starting.


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Sergei NAUGOLNYKH, SEVEN STEPS INTO PALEOZOIC // London: Libmonster (LIBMONSTER.COM). Updated: 27.09.2018. URL: https://libmonster.com/m/articles/view/SEVEN-STEPS-INTO-PALEOZOIC (date of access: 06.12.2021).

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