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The era of aquatic animals

About 540 million years ago, the pace of the evolution of organisms was so fast that this period is sometimes called the explosion of life in oceans. Ocean waters filled with numerous and diverse species, among which there were cnidarians, annelids, crustaceans and molluscs, a bit later also placodermiPlacodermiplacodermi appeared.

The bottom of the sea was inhabited by sponges and other marine animals living in sedentary environments such as corals and crinoids. Primitive cephalopods nautilida and ammonites were flitting in the midwater. The most characteristic animals of that period were the trilobites (belonging to arthropods), the ancestors of today’s crayfish.

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Ilustracja przedstawia erę zwierząt wodnych, the era of aquatic animals. Actual sizes of presented species: Nautilica, up to 350 cm, Ammonite, from a few up to 250 cm, Placodermi circa, 150 cm, Eurypterid, 200 – 250 cm, Trilobite, from a few up to 70 cm, Agnatha, 20 cm, Opabinia, 7 cm, Conodont, 1 – 40 cm, Pikala 5cm.

The period between 416 and 359 million years ago is the time of the rise of groups of fish. Many evolutionary lines developed then, the first of which were the fish with cartilaginous skeletons, similar to the contemporary sharks and rays. Fish covered in scales with fossilized skeletons appeared later; many of these species survived until today.

Soon, among fish inhabiting shallow waters, species with strongly muscled paired fins developed, thanks to which they could crawl through the shallows. Single fins were no longer useful in this environment, and started to vanish gradually in subsequent generations. Moreover, the upper or the lower segments of digestive tract were gradually gaining the ability to extract oxygen from the atmosphere. Fish with similar characteristics to those described above, have given rise to the first terrestrial quadrupeds - amphibians.

First terrestrial organisms

For over 3 billion years, life had been developing almost exclusively in water. Forms such as fungi, plants and animals appeared on land just about 500 million years ago.

The first organisms that inhabited lands about 480 million years ago were plants similar to today’s mosses.

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Ilustracja przedstawia olbrzymią ważkę Meganeura na tle drzewiastych paproci. Siedzi pionowo na pniu, czarna głowa u góry. Dwie pary błoniastych skrzydeł rozpostarte na boki.

The rapid and abundant development of plants took place during the warm and humid climate of geological period called CarboniferousCarboniferousCarboniferous. Dense vegetation provided food and shelter to numerous invertebrates, which appeared on land already 440 million years ago and diversified greatly. They developed organs adapted to breathing oxygen from the atmosphere and chitin cuticle that protected them against drying. The lack of competition from vertebrates that were still absent on the land, resulted in countless species of insects, up to 1 meter long, flying around in the air.

When about 395 million years ago the first amphibians appeared, the abundance of arthropods and other invertebrates was an easily accessible source of food for them, while at the same time they were not threatened by the still absent mammals and birds. Amphibians quickly took over all terrestrial environments and evolved into diverse forms. Some of them, such as Acanthostega still lived in the aquatic environment; others, like Ichthyostega, crawled on land, using their widely spaced paws to push, while Seymouria were moving using their limbs located right under the torso, just like typical terrestrial quadrupeds.

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Grafika przedstawiająca erę wczesnych zwierząt lądowych – dominację płazów, the era of early terrestrial animals. Na lądzie widać las karboński: drzewiaste widłaki, Lycophyta, paprocie drzewiaste, Tree fern skrzypy, Calamites, nieliczne nasienne kordaity, Cordaitales. Zwierzęta na lądzie to: ogromna ważka, Dragonfly, ichtiostega (wychodząca z wody), Ichthyostega, akantostega, Acanthostega, sejmuria, Latimeria, dimetrodon (gad ssakokształtny), a zwierzęta wodne to ryba trzonopłetwa oraz ryba pancerna, Placodermi.

After the many‑million‑years of their domination, most amphibians went extinct. The few remaining species gave rise to the amniotic animals - reptiles.

The era of reptiles

Reptiles were the first vertebrates to become independent from the aquatic environment. Their eggs, equipped with an embryo food supply and a strong, leathery or calcareous coating, could be laid anywhere on land. The animal leaving the egg was completely independent and protected from the loss of water by dry, thick skin.

The largest growth of reptiles took place between 250 and 66 million years ago. This period is called the Mesozoic EraMesozoic EraMesozoic Era, or the era of reptiles, because this is when these animals gained control over all available habitats at that time: the waters were dominated by Plesiosaurs and Ichthyosaurs, over the land and the water flew Pterosaurs, whose front limbs were transformed into wings, while the land was dominated by two‑legged predatory Tyrannosaurids and four‑legged herbivorous Sauropods, Stegosaurians, Triceratops. The age of reptiles ended 65 million years ago with their great and violent extinction, which killed not only reptiles, but also other animals (including aquatic) and most plants.

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Ilustracja przedstawia charakterystyczne rośliny i zwierzęta mezozoiku, erę gadów, the era of reptiles. Po lewej stronie widoczne jest morze, a w nim pływający plezjozaur, ichtiozaur oraz mezozaur polujący na ryby. Powyżej, w powietrzu szybuje pterozaur. Prawa strona ilustracji to ląd porośnięty drzewami i innymi roślinami, po którym spacerują zwierzęta: stegozaur, zauropod, triceratops, tyranozur, diplodok. Po prawej, na drzewie wspina się archeopteryks.

The era of mammals and birds

The extinction of most reptiles resulted in many free habitats and food sources that were exploited by rapidly diversifying mammals and birds. This was fostered by a world dominated by flowering plants with lush leaves, nutritious flowers and fruit.

First mammals, like their ancestors – the reptiles, laid eggs. In many mammalian development lines, however, a new way of reproduction has emerged - viviparity . Their teeth were also diversified, which enabled them to make better use of their food.

23 million years ago, more and more species of mammals lived on the continents, including hoofed mammals, predatory mammals, and the first primates - ancestors of modern monkeys and prosimians, from which lines leading to the hominids soon emerged. Some mammals started to repopulate the waters of the seas and oceans.

Birds have developed from reptiles belonging to one of the groups of dinosaurs. Important stages in the evolution of birds were the improvement of gas exchange, the transformation of the front limbs into wings and the covering of the body with light and flexible feathers. Soon after the major disaster 65 million years ago, new species of birds occurred, resembling those that live today.

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Grafika przedstawia charakterystyczne rośliny i zwierzęta kenozoiku, erę ssaków i ptaków, the era of mammals and birds. Po lewej stronie widoczne jest morze, a w nim pływający prawaleń, ancient whale. Powyżej, w powietrzu szybuje prehistoryczny nietoperz, bat oraz olbrzymi ptak morski, huge bird. Prawa strona ilustracji to ląd porośnięty drzewami i innymi roślinami, po którym spacerują zwierzęta. Wooly rhinoceros, giant deer, horse’s ancestor, sabre-toothed cat, cave bear, mammoths. W prawym, dolnym rogu – skały, w których człowiek, human ubrany w zwierzęce skóry czatuje na stado nadchodzących mamutów. Organizmy są podpisane.

Summary

• Life was created in the seas.

• In the history of life on Earth, you can find many examples of massive species extinctions.

Keywords

Placodermi, Seymouria, Mesozoic, Carboniferous

Glossary