Plant and Animal Life of the Tertiary Period: Paleogene and Neogene Flora and Fauna
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The plant and animal world formed over billions of years through a long chain of events that began with the formation of Earth itself and continued through the rise of the first cells, the greening of the land, the age of dinosaurs, and the spread of mammals. Archaeological and fossil finds from the Tertiary period of the Cenozoic era — the Paleogene (more detail: The Geological Age of the Earth) — capture one richly documented chapter of that story, but the full picture stretches from the origin of life to the present diversity of plants and animals. This article traces that whole arc, then looks closely at the well-preserved Tertiary record.
How the plant and animal world formed
The plant and animal world formed through evolution: a gradual process in which living forms changed across generations as the environment, climate, and geography of Earth shifted. Life began with simple single-celled microbes and, over roughly 3.8 billion years, diversified into the plants, animals, fungi, and microorganisms alive today. Each major step — the first cells, photosynthesis, multicellular bodies, the move onto land, and the rise of mammals — built on the one before it, and the Tertiary fossils described later in this article belong to one of the most recent and best-recorded of those steps.
Origin of life: from the first cells to multicellular organisms
Life on Earth began with simple chemistry. Before any cells existed, the early planet held the basic chemical building blocks — water, carbon compounds, and dissolved minerals — that could combine into more complex molecules. The leading scientific idea for how living matter first arose from non-living matter is called abiogenesis, the gradual chemical assembly of self-copying molecules that became the foundation of molecular biology and, eventually, the first cells.
The earliest signs of life are extremely old. Possible microbial traces have been found in the Nuvvuagittuq Greenstone Belt in Quebec and in ancient rocks of Greenland and Western Australia, dating to more than 3.5 billion years ago. All living things appear to descend from a single ancestral population known as LUCA, the Last Universal Common Ancestor, from which both major lines of simple cells — bacteria and archaea — diverged.
The first life forms were prokaryotes: tiny cells without a nucleus, represented today by bacteria and archaea. Among them, cyanobacteria were transformative because they evolved photosynthesis, using sunlight to make food and releasing oxygen as a by-product. Over hundreds of millions of years this released oxygen built up in the air during the Great Oxidation Event (also called the Great Oxygenation Event), permanently changing the atmosphere and making the planet habitable for oxygen-breathing organisms.
Development of eukaryotic cells
Eukaryotic cells — cells with a nucleus and internal compartments — were the next great leap. Eukaryotes arose when one prokaryote engulfed another and the two began living together. The energy-producing mitochondria inside today's complex cells descend from free-living proteobacteria absorbed in this way. This partnership gave eukaryotes far more energy and complexity than simple cells, and it set the stage for the kingdoms of complex life — including Protista (Protista), Chromista, plants, fungi, and animals.
Multicellular life followed once cells learned to cooperate and specialise. Instead of living alone, eukaryotic cells formed bodies in which different cells handled different jobs. The evolution of sexual reproduction accelerated this diversity by reshuffling genes in every generation, supplying the variation that natural selection could act on. The earliest large multicellular organisms appear in the fossil record as the Ediacara biota, soft-bodied creatures of the Ediacaran period that preceded the explosion of animal life.
The beginnings of animal life and the Cambrian Era
Animal life expanded dramatically during the Cambrian Era. Roughly 540 million years ago, at the start of the Phanerozoic, a burst of diversity known as the Cambrian explosion produced almost all the major animal body plans in a geologically short span. Among the most important innovations was Bilateria — animals with a symmetrical left and right side, a front and a back — a body plan shared by most animals today, from insects to humans.
This period left abundant fossils because many Cambrian animals developed hard shells and skeletons that preserved well. Invertebrates — animals without backbones — dominated the early seas, but the first vertebrates, simple fish-like animals with a notochord, also appeared. The Cambrian record is the moment when the modern tree of animal life truly takes shape.
Geological eras and their role in shaping life
Geological eras provide the timeline against which all of life's history is measured. Earth's formation began about 4.5 billion years ago from dust and rock circling the young Sun. Shortly after, a Mars-sized body called Theia is thought to have collided with the early Earth, ejecting debris that formed the Moon. A later phase of intense asteroid impacts, the Late Heavy Bombardment, battered the young planet before its surface cooled enough for stable oceans — and life — to take hold.
The universe itself is far older, originating in the Big Bang roughly 13.8 billion years ago, which produced the matter and energy from which stars, planets, and Earth eventually formed. Fossils, combined with the radioactive dating of rocks, let scientists place each evolutionary event in this vast timeline, from the earliest microbes to the Tertiary animals described later on this page.
Formation of continents and land
Dry land had to form before life could colonise it. Earth's crust slowly cooled and thickened into continental land masses that drifted, collided, and split apart over hundreds of millions of years. The arrangement of continents — including regions later known as Africa, South America, India, Australasia, Southeast Asia, and the area around modern Greenland — controlled climate, sea levels, and where species could spread, shaping the distribution of life across the globe.
Climate of the Paleogene and habitat conditions
The climate of the Paleogene (the lower part of the Tertiary system) was so warm and humid that lush vegetation grew even in Greenland and on the Svalbard islands.
Europe at that time lay in a subtropical zone. Its landscape was widely covered by palms — fan palm, date palm, and other evergreens such as dracaena, ficus, laurel, and magnolia — alongside trees of temperate climates such as oak and plane tree; conifers, besides cypress and sequoia, were represented by pine and fir.
Effect of climate change on plant development
Climate change has repeatedly redirected the course of plant evolution. As global temperatures fell after the warm Paleogene, heat-loving palms and evergreens retreated and were replaced by hardier conifers and deciduous trees, and later by grasses and steppes. Plants that could tolerate cooler, drier conditions survived and spread, while those adapted to tropical warmth declined — a clear example of natural selection acting on plants. The same pressure operates today, as shifting climate again rewards species able to adapt and threatens those that cannot.
Evolution of the plant world
Plants evolved from aquatic green algae and gradually conquered the land. The first land plants were small and non-vascular, like the ancestors of today's mosses; later groups developed internal tubes to carry water, allowing them to grow tall and spread into drier ground. From these beginnings came ferns, conifers, and finally the flowering plants that dominate today.
Vegetation of the Paleogene
The vegetation of the Paleogene corresponded almost entirely to that of today.
Vegetation of the Neogene and the spread of steppes
In the lower division of the Neogene, Europe's climate was still hot: forests held palms and evergreen vegetation (magnolia, laurel, cinnamon trees, and others). As the climate worsened, palms disappeared from the forests and were replaced by conifers and deciduous trees — plane, oak, beech, maple, elm, linden, poplar, birch, willow, as well as hazel, grapevine, and others.
Herbaceous plants developed and grasses appeared. Steppes became widespread, providing the open grazing land that would later support large herds of mammals.
The transition of plants from water to land
The move of plants from water onto land was one of the most important events in the history of life. Plants evolved from green algae living in shallow water; to survive out of water they had to develop ways to avoid drying out, stand upright, and reproduce on land. Early forests that grew from these pioneering plants also helped create the first true soils, as decaying plant matter broke down rock and enriched the ground — a feedback that made the land ever more hospitable.
Plant reproduction diversified as plants adapted to land. Ferns reproduce by releasing spores that are dispersed by wind and water, a method inherited from their water-bound ancestors. Seed plants later evolved pollination — the transfer of pollen, often carried by wind or by insects such as the honeybee — followed by germination, in which a seed sprouts and a seedling begins to grow. Flowering plants, including early forms such as Archaefructus, combined flowers, pollination, and protected seeds into a reproductive strategy so successful that flowering plants now make up most of the world's plant species.
Cooksonia as a transitional plant species
Cooksonia is one of the earliest known vascular land plants and a key transitional fossil. Cooksonia was a small, leafless plant with simple branching stems tipped by spore-bearing structures, living more than 400 million years ago. Fossils of Cooksonia have been described from sites including Devonshire, Somerset, and other parts of the British Isles, and they show the crucial step at which plants gained the internal tissue needed to stand upright and transport water on dry land.
Evolution of the animal world
The animal world of the Tertiary period is highly distinctive — it is above all the kingdom of mammals. A careful study of how the animal world developed over this time lets us trace the successive appearance of modern forms, whose number grew continuously and, by the beginning of the Quaternary period, already amounted to 95%.
The strange "antediluvian" animals, as they were once called, vanished from the stage of life right at the boundary between the Cretaceous and Tertiary periods.
The animal world of the marine basins
We begin our acquaintance with the animal world of the Tertiary period in the marine basins. Here, among the simplest organisms, the rather large rhizopods called nummulites became exceptionally widespread. In Latin "nummus" means a small coin of change.
The shells of nummulites are indeed similar in shape and size to coins. They form thick beds of nummulitic limestone. In the Paleogene, corals, bivalve and gastropod molluscs were also widespread (the shell of the latter is often coiled into a cone).
Bivalves, or bivalve molluscs, live mainly in the coastal zone: they lie freely on the seabed or even attach themselves to it. Some forms burrow into the substrate. Gastropod molluscs are represented by both terrestrial and aquatic forms — freshwater and marine. They live mainly at shallow depths.
Among the animal life of the basins, bony fish came to predominate, as well as sharks that sometimes reached gigantic sizes. An example is the famous Carcharodon, otherwise "sharp-toothed" (from the ancient Greek "carcharos" — sharp-toothed). The gaping maw of this sea monster, armed with sharp dagger-like teeth, could be compared to an open double door.
Four tall men could have fitted freely inside such a mouth.
Reptiles, until recently the masters of land, water, and air, yielded their dominant position to other classes of vertebrates better adapted to the changed conditions of existence. In the end, bony fish prevailed in the aquatic environment, birds in the air, and mammals on land.
The animal world of the land
On land, the advantage of mammals showed itself above all in the fact that they fed their young with mother's milk and cared for them, taught them useful skills in recognising and obtaining food, and finally protected them from numerous enemies. Reptiles have no bond with their offspring, and the number of eggs a female lays is, in general, not very great.
The young that hatch from the eggs must lead an independent life from their very first steps: finding food themselves and defending themselves against enemies. Birds — both precocial, like hens, which immediately begin acquainting their chicks with the surrounding environment, and altricial, like sparrows, which feed their nestlings for a long time — were more resilient compared with reptiles and amphibians.
A bird's body is reliably protected from temperature fluctuations by feathers and down, while the body of most mammals is protected by fur and underfur (mammals living in water are well protected by a layer of fat).
Moreover, birds and mammals, as warm-blooded animals, were not affected by the temperature of the surroundings, and a sharp cold snap did not bring all life processes to a halt as it did in cold-blooded reptiles and amphibians. At the beginning of the Tertiary period, one of the most ancient groups of primitive mammals gave rise to their modern orders: rodents, ungulates, carnivores, and many others.
The first representatives of these orders were still very primitive compared with their later descendants.
The most ancient predators
The most ancient predators combine in themselves not only the features of true carnivores but also those of other ancient mammals. In Miocene times, for example, such a beast was the sabre-toothed tailless tiger — Machairodus (from the ancient Greek word "machaira" — sword, dagger).
In size, Machairodus far exceeded the Amur and Bengal tigers. Judging by the structure of its teeth, it could attack such thick-skinned animals as ancient rhinoceroses and elephants. Opening its terrible maw wide, almost at a right angle, it evidently easily pierced the thick hide of its victim like daggers. Some representatives of the animal world remained, by their origin, as if apart from other animals.
Such, for example, is Arsinoitherium — "strong beast" (from the ancient Greek words "arsen" — manly, strong, and "therion" — beast). It was the size of a rhinoceros (about 3.5 metres long).
Its characteristic features were widely splayed toes on powerful limbs and impressive cone-shaped horns on the nasal bones, fused at the base and slanting forward, with a pair of short, goat-like horns behind them. Arsinoitherium may be a distant relative of the elephant. No less peculiar was a representative of the odd-toed order, the giant hornless rhinoceros — Indricotherium.
A beautifully preserved skeleton of it was discovered in the rich Turgai rhinoceros graveyards (in the Aktobe region of Kazakhstan). It is exhibited in the Palaeontological Museum of the Academy of Sciences in Moscow. Indricotherium was considerably larger than an elephant.
This is emphasised in the animal's name, derived from a fabled monster, since "Indrik — the beast — is the mother of all beasts..." The skull of this extinct forest giant was over a metre long, and yet its head seemed small compared with its enormous body; its shoulder height exceeded 5.5 metres, and it had a long, giraffe-like neck; its front legs were higher than the hind ones and in their build resembled an elephant's.
With such a body build, Indricotherium, strolling through a modern city, could — like Brachiosaurus — even peer into second-floor windows. A match for Indricotherium was one of the ancestors of modern elephants, Deinotherium, translated from ancient Greek as "terrible beast" (from "deinos" — terrible and "therion" — beast). From the lower jaw of this truly terribly enormous animal hung two impressive tusks, sharply curved downward.
The Mastodon, which lived at the same time, resembles an ancestor of the elephant more in general appearance. Its name notes the peculiarity of its molar teeth, which had a tuberculate surface (in Greek "mastos" — breast, nipple, and "odous" — tooth). Mastodons were roughly the same size as elephants; they had a well-developed trunk and two pairs of straight tusks — upper and lower.
Among the later Tertiary animals, Sivatherium especially stands out — a giant buffalo-like giraffe. Its name comes from the place of its discovery — the Siwalik Hills (the southern foothills of the Himalayas in the Punjab, within India). Its huge head, the size of an elephant's, was adorned by two pairs of horns — small ones above the eyes and behind them massive, flattened ones of unusual shape.
The transition of animals from aquatic to terrestrial life
Animals first colonised the land by evolving from aquatic vertebrates into the first amphibians. Fish living in shallow waters during the Devonian developed limb-like fins and the ability to breathe air, allowing them to crawl onto land. From these pioneers came the amphibians, which still return to water to breed, and later the reptiles, which evolved waterproof eggs that freed them from water entirely. This sequence — fish, amphibians, reptiles — is the backbone of vertebrate evolution onto land.
Major body plans of animals
Animals are organised around a small number of fundamental body plans established early in their history. The most successful is Bilateria, the bilaterally symmetrical plan with a head end, a tail end, and matching left and right sides, shared by insects, fish, reptiles, birds, and mammals alike. Within the vertebrates, the basic plan of a backbone surrounding a nerve cord was modified again and again to produce fish fins, amphibian limbs, bird wings, and mammalian legs — variations on a single inherited design.
The age of dinosaurs and their extinction
Dinosaurs dominated the land for roughly 165 million years before going extinct. They evolved from early reptiles and diversified into countless forms, including plant-eaters such as the plated Stegosaurus and the horned Triceratops, which consumed the abundant vegetation of their time. The age of dinosaurs ended abruptly with the Cretaceous-Paleogene extinction event around 66 million years ago, almost certainly triggered by a massive asteroid impact. The disappearance of the dinosaurs cleared the way for mammals to rise — the very mammals whose Tertiary descendants fill the fossil record described above. Birds are the living descendants of dinosaurs, the only branch of that great group to survive the extinction.
The predominance of mammals and care for offspring
Mammals rose to dominance after the dinosaurs vanished, diversifying rapidly into the orders alive today. A key reason for their success is parental care: mammals nourish their young with milk and protect and teach them, giving offspring a far higher chance of survival than the unattended eggs of reptiles. Mammal diversification produced lineages as varied as the pouched marsupials of Australasia and South America and the placental mammals — including big cats such as lions and tigers — that spread across the other continents. The same warm-blooded biology and parental investment that helped Tertiary mammals flourish underpins the success of mammals today.
Animal life cycles and their stages
A life cycle is the series of stages a living thing passes through from its beginning to the point where it produces the next generation. Every plant and animal has a life cycle, and comparing them reveals both shared patterns and striking differences. The vocabulary of life cycles — terms such as egg, larva, juvenile, adult, reproduction, and metamorphosis — describes these stages, and life cycle diagrams are commonly used to show them as a repeating loop, since the cycle begins anew with each generation.
The cycle of birth, growth, reproduction, and death
The basic life cycle of most animals follows four stages: birth, growth, reproduction, and death. In a human, the cycle runs through infancy, childhood, adolescence, adulthood, and old age, with Homo sapiens reaching reproductive maturity only after many years of slow growth. A dog passes through similar but faster stages — puppy, juvenile, adult, and senior — while a gorilla, like other primates, grows slowly and depends on its mother for years, a pattern that mirrors human development. In each case, the cycle closes when one generation reproduces and gives rise to the next.
Metamorphosis: the example of the butterfly and caterpillar
Metamorphosis is a dramatic life cycle in which an animal changes body form completely as it matures. The clearest example is the butterfly: an egg hatches into a caterpillar, which feeds and grows, then forms a chrysalis in which its body is rebuilt, and finally emerges as a winged adult butterfly. This four-stage transformation — egg, larva, pupa, adult — is typical of metamorphosis in insects and lets the young and adult stages exploit completely different foods and habitats, reducing competition between them.
Comparing the life cycles of different species
Life cycles vary widely across species, reflecting different survival strategies. Some animals undergo metamorphosis, while others simply grow larger while keeping the same body plan:
- Butterfly — complete metamorphosis through egg, caterpillar, chrysalis, and adult.
- African Bullfrog — eggs hatch into a tadpole that lives in water, then transforms into an air-breathing adult frog, an amphibian life cycle that links water and land.
- Dog — direct development through puppy, juvenile, adult, and senior stages without metamorphosis.
- Gorilla — slow primate growth with prolonged maternal care from infant to mature adult.
- Human — the longest childhood of all, passing from infant to adult over many years.
Comparing the African Bullfrog's water-to-land transformation with the gorilla's steady growth shows how the same underlying idea — birth, growth, reproduction — produces very different journeys depending on a species' environment.
Darwin's theory of evolution and natural selection
Charles Darwin explained how the diversity of life arises through evolution by natural selection. His theory holds that individuals vary, that more offspring are born than can survive, and that those best suited to their environment survive and reproduce, passing their advantageous traits to the next generation. Over many generations this gradual selection reshapes populations into new species. The Russian scientist V. O. Kovalevsky (1842–1883) made a valuable contribution to understanding the laws of life's development on Earth; he brilliantly demonstrated the possibility of reconstructing, from fossil remains, the way of life of extinct animals, their kinship with other animals, and their developmental history, and his research brought the young scientist wide renown in world science.
Darwin's insights were shaped partly by birds. The ornithologist John Gould helped Darwin recognise that the finches he had collected were distinct species adapted to different conditions — evidence that fed directly into his theory. The modern understanding of evolution adds a genetic foundation Darwin lacked: traits are carried by genes, inherited from parents, and altered by mutation, the random changes in genes that create the variation on which natural selection acts. Comparing fossil animals with their living descendants, as on this page, reveals many differences; on the basis of a fierce struggle for existence and the natural selection of hardier organisms better adapted to new conditions of life, modern forms developed.
Animal life of the second half of the Tertiary period
During the second half of the Tertiary period, significant climate changes occurred — the great glaciation gradually advanced. The Quaternary period was beginning, representing an alternation of harsh glacial epochs with warmer interglacial ones. Strong cooling could not but affect the vegetation and the animal world.
The advancing glacier shifted vegetation from north to south. In interglacial epochs — when the glacier retreated — plants returned to their former places. During cooling, tundra vegetation — polar mosses, dwarf birch, polar willow, and other plants — occupied much of central Europe.
With the onset of a warmer interglacial epoch, deciduous and coniferous species characteristic of a moderately cold climate appeared here. Similar repeated migrations from north to south and from south to north also occurred in the animal world. Animals more adapted to a cold climate appeared. The Tertiary proboscideans were replaced by the mammoth, with enormous tusks up to 3 metres long.
In size it surpassed the elephant and was covered with long dark-brown fur that protected it from polar cold. A well-preserved mammoth carcass was discovered at the beginning of the 20th century in the frozen soil of the Berezovka River valley in Yakutia.
Its mounted specimen is in the Zoological Museum of the Academy of Sciences in St. Petersburg. The Quaternary rhinoceros, considerably larger than the modern one, was also covered with thick fur, which is why it was called the "woolly rhinoceros". On its nose were two horns — a large front one (about 0.5 metre) and a smaller rear one.
Mammoths and rhinoceroses are known not only from numerous finds of individual bones and complete skeletons, but also from well-preserved carcasses. They are found in the permafrost soils of the Far North and in asphalt seeps, in so-called asphalt swamps. Prehistoric man left, on the walls of the caves in which he lived, many remarkable drawings of beasts.
In very clear, artistically executed drawings. He also depicted beasts on bone, which he used for various objects. In that era there still lived such remarkable animals as the giant deer, whose head was crowned with mighty antlers spanning 3 metres; the huge cave bear; the primeval bull — the "buy-tur" of ancient Russian legends — and the wild horse and musk ox that have survived to our day.
Great help in studying the mammals of the Quaternary epoch is provided by the richest natural graveyards of fossils. They occur in many places: in the Far North, in the steppes and deserts of the south, in the area of the seas, and especially in the coastal cliffs of many rivers. Bolshoy Lyakhovsky Island, the southernmost of the New Siberian archipelago, can be called a mammoth graveyard that promises many more interesting finds.
One of the world's largest accumulations of bones of Tertiary animals, especially of the most ancient ancestors of the horse, is located near the city of Pavlodar (East Kazakhstan region). For several kilometres along the Irtysh stretch the richest bone-bearing layers here, whose total thickness reaches 12 metres.
This richest graveyard evidently formed in the broad channel of a deep Tertiary river, which after devastating steppe fires and the catastrophic floods that followed carried away the corpses of perished herbivores and the predators that hunted them. Many valuable finds come from the localities of fossil remains in the area of the Sea of Azov and the Aral Sea, as well as in the quarries near the city of Odessa, called catacombs, and in many other places.
Stages in the development of the horse
A careful study of fossil remains found in deposits of the Tertiary system of various ages allows us to trace how the plant and animal world formed successively at that time.
Thus, from the small five-toed little beast Eohippus, the size of a lapdog, the modern single-toed horse gradually developed.
- Translated from ancient Greek, Eohippus means "dawn of the horse" or "beginning of the horse" (from the words "eo", short for "eos" — dawn, and "hippos" — horse).
- The next, larger form, which lived somewhat later, was Orohippus, i.e. "border of the horse" or "almost a horse" (from the word "oros" — border, boundary). Then came Mesohippus, i.e. the middle, or intermediate, form of the horse, the size of a sheepdog. Merychippus (meaning "already formed horse") resembled a small breed of horse — the pony.
- The later Pliohippus (translated as "more horse") was already a larger and heavier-built but still small horse.
- The modern single-toed horse.
In all these ancient forms of the horse's development, characteristic features of the body's structure took shape over approximately 52 million years; the size of the original form increased and, in connection with the successive transformation of the five-toed limbs into single-toed ones, speed of running improved.
Adaptation to new environments and geographic distribution
Species spread across the globe by adapting to new environments, and where they can live shapes where they are found. As climates and continents changed, populations that could tolerate new conditions expanded into fresh territory, while barriers such as oceans and mountains kept others isolated. Isolation allowed separate populations to evolve independently, which is why the marsupials of Australasia differ so sharply from the placental mammals that dominate Africa, Europe, and the Americas. The horse lineage traced above is itself a story of adaptation, as successive forms grew larger and faster to thrive on open grasslands.
Biodiversity and the distribution of species
Biodiversity — the variety of living things — is unevenly distributed across the planet, shaped by climate, geography, and evolutionary history. Warm, stable regions tend to hold the greatest biological diversity and species complexity, while harsh environments support fewer kinds of life. Mass extinction events have repeatedly reset this diversity: the Permian-Triassic extinction event wiped out most marine species, the Late Devonian extinction event struck early sea life, and the Cretaceous-Paleogene extinction event ended the dinosaurs. After each loss, surviving lineages diversified to fill the empty roles. Today human activity is driving a new wave of species loss, and climate change is again testing which species can adapt and which will disappear.
Biological systematics and classification
Biological systematics is the science of naming and grouping living things according to their relationships. The framework still used today was created by Carolus Linnaeus, who introduced the two-part naming system and ranked organisms into nested groups from broad kingdoms down to individual species. Modern classification reflects evolutionary descent, placing organisms together when they share a common ancestor — which is why birds are grouped near reptiles and dinosaurs, and why humans sit among the primates. Institutions such as the American Museum of Natural History maintain vast collections of specimens and fossils that researchers use to refine this tree of life; science writers such as Hayley Dunning, and scholars including David Christopher and Peter B. Heller, have helped communicate how these classifications and the evidence behind them are understood. Tools such as genetic engineering and the wider field of molecular biology now allow scientists to read genes directly and confirm relationships that earlier naturalists could only infer from anatomy.
This continually updated tree of life connects every topic on this page — from the first prokaryotes, through plants, dinosaurs, and mammals, to the life cycles of the butterfly, the dog, and the gorilla — into a single shared history of how the plant and animal world formed.
