hva er en fossil

  Blida til en trelobes fossil

 fossil is any evidence of prehistoric life. This evidence can consist of actual remains, like bones, teeth etc., but also prints (e.g. from leaves) and foot prints.

Paleontology is the study of fossils. This is often confused with archaeology, the study of the rise of humans and their cultures. The paleontology studies the period between the origin of life (approximately 3.7 billion years ago) and the rise of the human culture about 10,000 years ago.

Fossils have intrigued man for generations. The Greek philosophers saw them as curious, natural phenomena that were formed in the earth the same way as crystals. Some people also thought they were proof of the biblical Flood. Leonardo da Vinci (1452-1519) suggested in his notebooks (correctly) that fossils were the remains of organisms that once lived, and that had turned to stone. In his time, his view was heretical; God would never allow his own creations to become extinct. His notes were suppressed, until they were published in the 19th century.

How is a fossil formed?

A fossil is formed when the remains of plants and animals are not eaten by scavengers or bacteria, but are covered by sand, soil, volcanic ashes, mud etc. soon after their death, so that oxygen cannot reach it. Usually only the hard parts of an organism will fossilize, like the bones. Only very rarely will softer parts fossilize.

The following processes can lead to fossilization:

Covering by sand, mud etc. This is the most common form. When a dead organism is covered by sediments, the pressure can be so high that the underlying sediments turn into stone. Freezing. A good example of this are the completely preserved mammoths in the permafrost (permanently frozen soil) of Siberia. (Below Mammoth tusk from the Permafrost).   Dehydration. Animals that die in dry caves can dehydrate and be preserved for thousands of years. Mineralization. Wood and bones are often preserved because the original cellular spaces are filled with minerals. Disintegration. If a buried organism decomposes, the space that is thus formed is a mould of the original organism. Pseudomorphism. If such a mould is filled with minerals, a cast of the organism is formed. How is the age determined?

This is often done by measuring the lead – uranium ratio in fossil bearing rocks. Very slowly, uranium turns into lead, with a half-life of millions of years. This means that you can get a relatively accurate dating by measuring the ratio of these two elements. The half-life is the time it takes for 50 % of the radioactive element to change into a stable, non-radioactive element.

The ratio between other radioactive and non-radioactive elements can also be used, e.g. between rubidium and strontium (rubidium changes into strontium) and potassium and argon (potassium changes into argon). Fifty percent of uranium 238 changes into lead 206 in approximately 4.5 billion years, 50 % of uranium 235 in 704 million years into lead 207, 50 % of thorium 232 in 14 billion years into lead 208, 50 % of rubidium 87 in 49 billion years into strontium 87, 50 % of potassium 40 in 1.25 billion years into argon 40, and 50 % of carbon in 5570 years into nitrogen. These radioactive elements were built when our solar system was formed and are in our atmosphere. When rocks are formed, they are ‘captured’ in these rocks and start to change into non-radioactive elements.

To take carbon as example: in 5570 years, half of the carbon is converted into nitrogen. For the remaining 50 %, it takes another 5570 years before half of it is converted into nitrogen. Now 25 % of the original amount of carbon is left. After another 5570 years, 1/8 remains, then 1/16, then 1/32 etc. Because of this relatively fast rate, carbon dating can only be used for the last 70,000 years. This is why it is often used an archaeology.

The above-mentioned method is also called absolute dating. The so-called relative dating is also often used. In this case, the age of a fossil is determined by using fossils from the same layer that are very common but have lived for only a short period of time (so-called trace fossils like ammonites and snails). If a fossil fish is found in the same layer as an ammonite from which we already know it lived only during the Upper-Cretaceous, the fish must be from the same period.

Most cosmologists agree that the universe was formed about 15 billion years ago. Everything was compressed into one block which had so much mass that at a certain moment it exploded; the Big Bang. A very weak microwave radiation, coming from all directions of the universe, is a remnant of that period. There is also other proof that the universe is still expanding in all directions.

The earth is about 4.6 billion years old. The moon and the planets seem to be of the same age. The sun (a star) is older, because it was formed first after the Big Bang. From the remaining matter the earth and other celestial bodies were formed. The oldest rocks on earth are four billion years old, which means it took 600 million years before the earth was cooled down enough to form the earth’s crust. At some places, this crust is 50 miles thick, while at other places it is so thin that lava flows out.

The earth’s crust is divided into a number of bigger and smaller plates. Lava streams upwards along the sides of these plates, pushing the plates apart. These plates also move (usually with only a few inches per year) because of the currents of the liquid rock in the earth. Mountains are formed when two plates push against each other. In this way, the Alps were formed because of the ‘collision’ between Africa and southern Europe. The plates can also move along, from or under each other. If this happens with big jumps, it causes earthquakes.

Moving continents function as rafts, bringing animals and other organisms from one part of the world to the other through the course of millions of years. In this way, continents can traverse through climate zones. For example, the southern part of Africa moved to tropical latitudes between the end of the Carboniferous and the end of the Triassic era. This had major consequences for the plant and animal life on earth.

How the continents were once divided can be determined by using fossils from plants and animals that must have had only a small area of distribution (especially from organism living along coasts), but from which the fossils are now found thousands of miles apart. Because fossils from the Precambrian are rare, we can only make a reconstruction of the division of continents beginning from the Cambrian.

From a geological viewpoint, life was formed very fast after the earth was cooled down. The oldest life forms are approximately 3.7 billion years old. In a unknown way, single-celled organisms were formed from chemical reactions in sea water. These were co-called Prokaryotes, which did not have a nucleus yet. Around this time, the first algae appear, so-called stromatoliths, built by layers of Prokaryotes. The first single-celled organisms with a nucleus were formed 2.1 billion years ago, the so-called Eukaryotes (Right an organism with nucleated cells).

We will probably never find out how life was formed. But the fact that the earth contains life is just a coincidence. All conditions for life are present on earth: enough sun light, the correct temperature, and water. For the formation and development of life we first need a stable mother star (in our case the sun), that delivers a constant flow of energy for billions of years. Life is than possible on a planet that is not too close to that star (otherwise it will be too hot) and not too far away (otherwise it will be too cold). The mass of the sun is also very important. If it would be 30 % more than it is now, the sun would be burned out after four billion years. Luckily, our sun will last for another five billion years or so, which means we are halfway now. Another condition is a very big planet like Jupiter which ensures that a small and vulnerable planet like the earth is fairly safe from comets and asteroids. The moon is also important. It makes sure that the position of the earth’s axis remains stable.

Single-celled organisms did not develop for two billion years, until multicellular organisms suddenly appeared about one billion years ago (in 1998 in India, trace fossils of multicellular worm-like organisms have been found in petrified sea sand that are 1.1 billion years old). That is probably because at that time the atmosphere contained enough oxygen for ‘higher’ organisms. During the era of the single-celled organisms, the earth was still free from oxygen. However, the single-celled organisms gave off oxygen (photosynthesis; plant cells take up carbon dioxide from the air, convert it into carbohydrates and give off oxygen as a waste product). The ozone layer in our atmosphere also consists of oxygen (O3 instead of O2), and probable also played a major role, because ozone protects life on earth from the ultraviolet radiation of the sun.                                      

Bilda til Hadean tid  fra 4.6 til 3.7 billion år det vær ikke live

Nowadays, the Precambrian is divided into three periods by scientists: The Hadean is the period from 4.6 to 3.7 billion years ago, in which there was no life yet. The Archean is the period from 3.7 to 2.5 billion years ago, in which stable continents formed and from which the first single-celled fossils are fairly common. The Proterozoic is the period from 2.5 billion to 570 million years ago, in which multicellular animals evolve.

About 570 million years ago an explosion of new life occurred. This new period is called the Cambrian.


Bilda til the Archean tid fra 3.7 til 2.5  billion years single-celled organisms were formed

The Northern Hemisphere consists of the continents Laurentia, Baltica and Sibiria, and the Southern Hemisphere of the supercontinent Gondwana, which includes current Africa, South America, Antarctica, western Australia, India and southern Europe. Big land masses are under water due to sea floodings. There are no continents around the poles.

Bilda til Proterozoic period from 2.5 billion to 570 million years ago in whish multicellular animals evolve

The first and widely spread fossils are from the Lower Cambrian era. The animals from this period (which only lived in the sea) had developed armatures (for support and protection against predators). Of course, their remains are better preserved than the softer animals from the Precambrian.

Many life forms had already developed in the sea water. Most animals were plant eaters living from algae. The oceans were inhabited by seaweeds, brachiopods (sea animals resembling mussels), sponges, worms, echinoderms, sea snails, jellyfishes, shellfishes, and segmented arthropods, the trilobites (so called because their body consists of three parts, ‘lobes’). From all life, the trilobites were the most developed. More than 15,000 species are known, varying in length from one mm to more than two feet. During the Cambrian, they accounted for approximately 60 % of the animal life.

At the end of the Cambrian the first fishes and vertebrates appeared. The spine served as protection against compression, as a ‘hatstand’ for the organs, and as a place of attachment for the muscles.

Bilda In Cambrian time 541 to 485 million years jewless fish evolve with bony skin not scales

De transition from the Cambrian to the Ordovician is characterized by the extinction of a lot of animal species. Others dramatically decrease in number, especially the trilobites, until then dominating. They will never reach their great versatility again.

 In Ordovic  time from 485 million to 443 years  the sharks evolve 

 Ordovician time the frist plants blue-green alge conquer the land

The northern part of what is now Central Europe separates from Gondwana and consolidates with Baltica into what is now northern Europe at the end of the Ordovician. Present southern Europe is still part of Gondwana, and is situated near the South Pole.

In the Ordovician, the first organisms conquer the land. The shallow seas of the Cambrian dry up during the outgoing tide, and blue-green algae are forced to survive without water for a short time. They were capable of facing the air and the sunlight for a few hours during the tidal cycle, not more. But they did contribute to the existence of life on land.

Water is a mixture of hydrogen and oxygen. By extracting hydrogen from water the blue-green algae released oxygen, which is essential for the production of energy that a lot of land animals need in large quantities. They can also extract nitrogen from the air. Nitrogen is necessary for building proteins, the materials of every organism. Thanks to the blue-green algae, the plants were able to move to land in the Ordovician. Saltwater plants moved to fresh water, and from there they reached the land.

The transition from the Ordovician to the Silurian is again characterized by large extinctions, possibly resulting from the drifting continents around both poles. If the pole regions are covered by land (just like the South Pole by Antarctica now), the ice layers become very thick and extensive, and the sea levels will thus drop. Because of the oceanic and atmospheric circulations to the rest of the world, the temperatures will decrease worldwide. This theory is supported by the fossils of the marine animals that have been found from that period; the number of different species is small and adapted to cold water.

In Silurian time scales fisk evolve from 443 to 419 millon year

Laurentia and present northern Europe come together and form the continent Euramerica.

The main difference in the fauna from the Silurian compared to that of the Ordovician is the presence of new families and genera, not so much the appearance of completely new animal groups. An important new ‘invention’ is the development of jaws. They probably evolved from the first row of gill arches. Until then, fishes had a mouth with which they could suck in food. The development of jaws and teeth was very important for the vertebrates, because it meant they could eat more different kinds of food than jawless animals. A lot of different carnivores arose, which in turn forced their prey to improve the ability to flee. The jawless fishes were partly or completely covered with bony plates. The ‘new’ fishes with jaws developed scales.

In the Silurian the first real land plants appear (not more than two inches high), with water-transporting tissue, a strong stem, and a wax-like outer layer to prevent water loss. However, they are still connected to the water by their means of reproduction with spores. The first animals also move from the water to the land; insects (still without wings) like spiders, centipedes and wood louses. The first vertebrates on land appear in the Devonian.

Bilda  in silurian time frist insects move to land like spider centipedes and wood louses 443 to 419 million years

The first trees originated in the Devonian. The plants develop seeds, so that they are not dependent on water anymore for their reproduction and can conquer the inland. But it is mainly the age of the fishes. In this period the temperature rose, so that lakes and rivers dried up. Some freshwater fishes became extinct, but others were able to move from one pool to the other using fleshy fin lobes; with other words, they started to ‘walk’. These so-called lobe-finned fishes were the first fishes to develop lungs.

Bilda  ned in Devonian time 419 to 359 millon years the frirst trees evolve

The lungfish and the Coelacanth are examples of lobe-finned fishes that still live today. Lungfish are freshwater fishes and also have gills, but during a period of great drought their swimming bladder serves as a lung. They then bury themselves in the mud. They use their pectoral and pelvic fins as legs. The Coelacanth (a saltwater fish) was thought to be extinct for millions of years already, until a living specimen and then a whole colony was discovered near Madagascar in 1938.

bilda In Devonian time also frist fish with lung and salamander and frogs like animals evolve

The amphibians evolved from the lobe-finned fishes. Amphibians like frogs and salamanders can live both in water and on land, but their eggs are laid in water. They also depend on water because of their skin. Although they have lungs, they also breath through their soft, wet skin. They have to make sure it doesn’t dry out.

Reptiles do no suffer from this problem. They breathe completely through their lungs, and lay eggs with a scale. Reptiles appeared in the Carboniferous.

Again, the transition from the Devonian to the Carboniferous is characterized by wide extinctions. About 25 % of all families dies out. From the ammonites, fishes, amphibians, corals and trilobites more than half of the families does not make it into the Carboniferous.

Gondwana and Euramerica approach each other and ‘collide’ at the end of the Carboniferous, causing big mountain ranges in the areas that are now Central Europe and North America.

This era is named after the coal that is formed during that period. It was a time with shallow, warm seas. On land the amphibians further develop, while the plants grow in all humid areas. The coal deposits resulted from these swampy forests, with some trees reaching 160 feet. The slow armoured fishes become extinct, while the predators (sharks etc.) develop further and speed and manoeuvrability start to play an increasingly important role. The first insects with wings appear.

The reptiles evolve from the amphibians. In the Upper Carboniferous they quickly spread out across the land. Due to improvements in their jaws and teeth they developed to bigger and better carnivores. They put great pressure on their prey animals, which had to develop a better defense or run harder. The development of eggs with a scale also played a major role. The eggs can now be laid on land, and the embryo is protected against dehydration.

The carboniferous period 359 to 259 million years is the age of reptiles and giant insects

The improvements to the jaw also enabled the reptiles to eat plants. The rise of the herbivorous reptiles meant a great incentive for the development of ecosystems on the land. The plants were forced to develop defense mechanisms. A tough cuticula (protective outer layer), leaves with a wax layer, sharp thorns and toxic substances probably originated in this period.

But the herbivores also had a positive influence on the plants. Seeds with a tough skin could be eaten, pass the digestive tract of the animal unharmed, and be secreted in the middle of a pile of dung, a perfect means of nutrition for the plants. In this way, the seeds could be spread across a wide area.

In turn, all kinds of different herbivores evolved that could eat the different plants, and this resulted in a great variety of carnivores to hunt the herbivores. A very complex network of evolutionary interactions formed on the land.

All continents (except current Asia) come together and form the supercontinent Pangaea. Current central Europa lies near the equator, while current Africa, India, South America and Australia are covered by ice. The amphibians and reptiles now also spread across Gondwana.

In this period a lot of new insects appeared like beetles and dragonflies. The latter can reach a wing span of more than two feet. Rivers and pools contain a wide variety of fishes. Amphibians thrive along the banks, but are already overshadowed by newer, more active reptiles.

One group of carnivorous reptiles, the cynodonts, already had clear mammal-like characteristics. They were the first to be able to breathe and chew at the same time without choking, because the nasal passage was separated from the oral cavity. By chewing the food before swallowing the digestive process is accelerated. This suggests the cynodonts had to have energy at their disposal fast. It is possible they used it to produce their own body heat. As opposed to their predecessors they were small animals. A small animal with a big surface in relation to its body volume will lose heat fast. There is evidence that cynodonts had hairs, so that they didn’t lose so much heat. The main characteristics of modern mammals are hairs, the production of body heat (warm-bloodedness), and the fact that they feed their young with milk from mammary glands. The cynodonts, which still laid eggs, seem to have passed the phase to real mammals for two-third.

The end of the Permian is also the end of the Paleozoic (‘first life’), which started with the Cambrian. A lot of animal and plant species became extinct, such as the trilobites, the giant scale trees, most horsetails and a lot of ferns. Amphibians and some fishes were dramatically limited. This was caused by extreme climate changes. One of the reasons were the drifting continents. In the Permian, the temperature on the southern continents rose because they moved north. Also, for the first time in history, the big land masses connected to one supercontinent at the end of the Permian. Big, mobile animals could spread out, resulting in less different types of animals.

So, the transition from the Permian to the Triassic is again characterized by wide extinctions. More than 80 % of all animal and plant species died out. The Triassic is the beginning of a period called Mesozoic (‘middle life’).

During the Triassic the reptiles not only spread out on land, but also in the water and in the air. Some reptiles decided to go back to the water, maybe because they could find more food there. The flying reptiles, the so-called pterosaurs, developed species with a wingspan of 50 feet, as big as a glider plane. However, modern birds did not evolve from pterosaurs, but from land reptiles, most likely from dinosaurs. Pterosaurs and birds, which first appeared in the Jurassic, together shared the air for almost 100 million years.

The dinosaurs appeared in the Mid-Triassic. The difference with other reptiles is the fact that their legs stand directly under the body, and not sideways anymore. This made their walk more efficient, and a bigger body weight could be carried.

The first real mammals also appear in the Triassic. Their young already grew in the womb. The advantage is that they are already fairly big and strong when they are born. But under the domination of the dinosaurs they stay only small and will only start to flourish after the dinosaurs have died out.

At the end of the Triassic there is another extinction wave, this time not so big. However, especially the ammonites, the amphibians and the reptiles on land suffer.

Dinosaurs evolved from smaller reptiles approximately 230 million years ago. They differ from other reptiles in the position of their legs: those of dinosaurs stand directly under their body, at other reptiles they stand sideways in a 90° angle. The advantage is the ability to simultaneously breathe and run for a long time. Other reptiles cannot do this. Their lung capacity is limited because of the constant bend of the body. Thanks to this completely improved walk the dinosaurs could grow larger and run faster and harder. This cleared the evolutionary road for an enormous diversity in body types and lifestyles. It should be noted that dinosaurs only lived on land. Pterosaurs and reptiles living in water are not dinosaurs.

During the Triassic there were no clues that they would soon rule the earth. At that time they were insignificant creatures, not bigger than a dog, surrounded by huge crocodiles and other reptiles. But for evolutionary standards they must have taken over quickly. 220 Million years ago a lot of other reptiles declined, while the dinosaurs filled the empty spaces. The early mammals, that emerged around the same time as the dinosaurs, played only a minor role for the next 165 million years.

The picture we have from dinosaurs has changed in the last few decades. They were not necessarily dumb, and did not wander around on their own, also not the carnivores. They took care of their young and worked together to protect themselves against predators. Instead of an even green or gray colour they could well have been brightly-coloured. New evidence even suggests they were warm-blooded. They were agile animals that could even move energetically with cold weather and some even lived above the polar circle. Most dinosaurs were as big as a pony. The smallest was as big as a chicken, the biggest (found until now) could reach a length of 140 feet (Seismosaur).

We will learn a lot more about dinosaurs this century, also since scientists discover a new species almost every few months. But two mysteries will probably never be solved.

The first issue is the question if birds evolved from dinosaurs. Different fossils of possible intermediate forms have been found. The most well-known of these is Archaeopteryx, an animal the size of a pigeon, of which various fossils have been found in the 150 million year old Solnhofen limestone in Germany. The bone structure resembles that of a dinosaur. It also had a reptilian head with teeth. But it also had feathers and wings, although they still had claws. One thing is sure though: birds did evolve from reptiles.  (Left Dinosaur Utah Raptor)

The second mystery is the question how dinosaurs became extinct. The prevailing opinion nowadays is that a big comet or asteroid hit the earth 65 million years ago. The resulting worldwide dust cloud obscured the sun for months or even years. Most vegetation died and the dinosaurs starved to death. The mammals now filled the empty spaces. This theory is supported by a thin layer of iridium, an element that is very rare at the surface of the earth but is fairly common in meteorites and asteroids, and that is found at the right height (at the border of the Cretaceous with the Tertiary) in the rock deposits.

On the Mexican peninsula Yucatan scientists have discovered a (subterranean) crater impact that has the ‘right’ dimensions and age. But there is also evidence that dinosaurs were disappearing anyway. The registration of fossils shows that the number of different species decreased with 70 % between 73 and 65 million years ago. The flying and swimming reptiles also declined in number. The cause of this decline is as yet unknown.

Pangaea slowly starts to fall apart and new continents are being formed. Current North America separates from Eurasia, thus forming the Atlantic Ocean. The overall climate is so warm that the poles are free of ice.

Possibly forced by the dinosaurs, more reptiles decide to go back to the sea. These reptiles evolve into plesiosaurs, ichthyosaurs and mosasaurs. The dinosaurs prosper, and some species can reach a length of more than 100 feet.

A small group of carnivorous reptiles, most possibly dinosaurs, now evolve into birds. They have reacted on a stimulation from the air, which had a rich food source in the form of hundreds of different species of insects. The bird skeleton was built from light, air-filled bones, reptile scales changed into primitive feathers on body and tail, but the claws still remained for a long time so that birds could climb into trees. These primitive birds were probably not capable of flying off from the ground, but could glide from a tree through the air for a short distance. After that, it was just a matter of time before this short gliding movement changed into real wing movements and birds really started to fly.

Gondwana now also breaks into pieces, which leads to the formation of Antarctica and Australia. India moves to the north and South America to the west. The Northern Hemisphere contains two continents: Asiamerica, consisting of current Asia and the western part of North America, and Euramerica, consisting of Europe and the eastern part of North America.

The Cretaceous was the forerunner of new plants and animals. The most important newcomers were the flowering plants. Many trees and bushes from the this period still exist today. The dinosaurs thrived, but became extinct at the end of the Cretaceous. This was probably a gradual process, since plesiosaurs and other marine reptiles were already extinct in the Middle Cretaceous. The pterosaurs, the remaining ammonites and some groups of bony fishes also died out. The lizards, snakes, crocodiles, sea turtles, amphibians, mammals, bivalves, birds and most plants remained untouched.

According to one of the first theories for this mass extinction, the atmosphere had changed because of high volcanic activity. This would be a disadvantage for the big reptiles, but an advantage for the more lively mammals and birds. About 65 million years ago the so-called Deccan Traps were formed in India. For a period of tens of thousands of years, lava streamed from the earth. The gas and dust from these eruptions must have disturbed the climate dramatically.

Another theory says that a big meteorite crashed on earth, or several small ones within a one-year period, throwing so much dust in the atmosphere that the sun was blocked for months or even years. Plants could not carry out photosynthesis, and the temperature fell drastically. Speaking out for this theory is the amount of iridium found in rocks that mark the border between the Cretaceous and the Tertiary. Iridium is a metal that is only found in small quantities in the crust of the earth, but which is fairly common in meteorites.

Most likely several disasters that occurred at the same time or right after each other were the cause. The fact is that the dinosaurs were replaced by the mammals, which quickly filled the empty spaces. Now that the big reptiles were gone, they went through an explosive development in the following periods.

The end of the Cretaceous is also the end of the Mesozoic. The new period, starting with the Tertiary, is called Kenozoic (‘new life’).

The continents get their recent shape and position, although Europe and North America are still connected at the beginning of the Tertiary, so that especially mammals can mix on both continents.

Most non-dinosaurian reptiles (lizards, snakes, turtles, and crocodiles) survived the mass extinction at the end of the Cretaceous. But although they had to chance to profit from the extinction of the dinosaurs, it were the mammals and birds that really thrived.

Mammals and birds have a few characteristics in common. The most remarkable of these is the fact that it are very intelligent and ingenious animals, with the ability to learn from experience. They often work together, forming herds or swarms that in some ways act as one big super organism. And they are of course warm-blooded: they produce their own body heat, so that they are not dependent on outer environmental conditions. They can live in cold areas that are too hostile for cold-blooded reptiles, which only become active after they have been warmed up by the sun.

The Paleocene marks the time of the adaptive spread of the mammals. The different animal species that are found in the fossil deposits from this period are not very big: small insect eaters and some very early primates. The first big waves of herbivorous mammals appeared in the Upper Paleocene. The carnivorous mammals are still small. The place of the big carnivores is taken by some unusually big cursorial birds (up to 10 feet high) with a very strong beak. They die out after the first carnivorous mammals appear.

In the Ecocene the mammals start to play the most important role in life on earth. They not only dominated the ecosystems on land, they also returned to the sea (whales and dolphins) and learned to fly (bats).

The geography of the earth is still changing in the Oligocene. Europe disconnects from North America. On the Southern Hemisphere, Antarctica is covered by ice. The rodents, like rats, mice, hamsters and beavers, now prosper. The big plant eaters have a big variety. Some of them are more than twelve feet high. The dogs and cats (among them the saber-toothed cats) also originate in the Oligocene.

In the Miocene the dramatic explosion of the mammalian fauna continues. The South Pole extends, so that it gradually gets colder. The dense rain forests are replaced by open grass lands that are able to feed even more mammals like horses, camels, deer, and elephants.

Because of the tendency to a cool and dry climate, the circumstances in the Pliocene can be compared with those of the present. The important vegetation types as we know them now originated in the Pliocene. A lot of specialized animal species became extinct and were replaced by animal types with a mixed diet that could better adapt to the changing conditions.

The mammoth

After the dinosaurs became extinct approximately 65 million years ago, the birds and especially the mammals fill up the empty spaces and start an impressive march. The ancestors of the mammoths emerged around 40 million years ago in Africa. These are the first proboscideans. The trunk resulted from the growing together of the nose and the upper lip. Elephants grew larger but the neck stayed short, so a trunk was needed to bring food and water to the mouth. The nostril is formed by a big hole at the point of attachment, so that the skull of elephants can easily be recognized.The first elephants evolved into more than 150 different species in the course of time, some of them with very long tusks (these are actually extremely elongated incisive teeth). The bloom of the elephants was in the Miocene.

About four or five million years ago in Africa the elephants divided into three lines. From the first one, the Loxodonta, the African elephant emerged. The Indian elephant probably evolved from the second one, Elephas. The third one, Mammuthus, gave rise to the mammoths. So, as is sometimes thought, the mammoths are not the ancestors of the current elephants.

About three million years ago the first mammoths appeared in Europe. They belonged to the species Mammuthus meridionalis, also called ancestral mammoth. It was bigger than the current elephants (13 feet high, weight 10 tons), and without hair (the climate was warm then). But it had bent tusks, which is a characteristic of mammoths. It also spread east to Asia, and crossed the Bering Land Bridge to reach North America about 1.7 million years ago when the climate was cold. When the temperature and thus the sea level rose again, the two continents were separated. In North America, the isolated M. meridionalis evolved into Mammuthus columbi (Columbian mammoth).

One million years ago the climate changed. The temperature became colder, and this changed the landscape in Europe. Woods changed into open grasslands. M. meridionalis died out, but not before a small population adapted to the changing conditions and evolved into Mammuthus trogontherii (steppe mammoth). Its molars had more ridges, so that they were more suitable for eating tough grasses.

Approximately 250,000 years ago in Europe, the woolly mammoth, Mammuthus primigenius, emerged from M. trogontherii. It was even better adapted to the cold. It was about as big as the Indian elephant (11 feet high), with a thick, long-haired woolly skin, a hypodermic fat layer, a short tail and small ears. M. primigenius is the last species of the Mammuthus family. If people say ‘mammoth’, they usually refer to the woolly mammoth. About 100,000 years ago the woolly mammoth was also able to reach North America through the Bering Land Bridge. But its range was limited to Alaska and Canada, while M. columbi preferred a milder climate and had moved south to the US and Mexico. In the rest of the world the woolly mammoth could be found in Europe and Asia.

Woolly mammoths are well-known because of their finds in the Siberian permafrost (constantly frozen soil). The animals are often so well-preserved that even skin, flesh and hair remain. In Europe, fishing boats often find remains in their nets, especially on the North Sea between Holland and England. In the Pleistocene era during the ice ages, the sea level was so low that animals (and humans) could live on the bottom of what is now the sea. (Right Woolly Mammoth lower Jaw)

At the end of the Pleistocene, 10,000 years ago, a lot of big mammals like the cave bear, cave lion, giant deer, steppe wisent, but also the mammoth, died out. On the one hand this was caused by the changing climate (it became warmer, so that the vegetation changed), on the other hand because of the influence of humans, which rose in number and developed more efficient hunting techniques.

Mastodonts are sometimes confused with mammoths. Mastodonts are a separate branch of the elephant tree. They emerged 35 million years ago in Africa. After that, they spread through Europe and Asia, and 3.7 million years ago to North America, where they evolved into the species Mammut americanum. Mastodonts resemble mammoths, but were smaller. (Mastodont)

The Pleistocene era is characterized by at least five important ice ages, in which the ice caps moved south in the form of enormous glaciers. The overall climate is so cold that the snow in the north does not melt. A big part of northern Europe, Asia and North America is covered by ice, which resulted in a worldwide climate change. However, the interglacial periods were warm, even subtropical. The most recent ice age ended about 10,000 years ago. A lot of big mammals became extinct then, like the mammoth, mastodont, giant deer, giant sloth, woolly rhinoceros, and saber-toothed cat.

One of the reasons for these extinctions were the fast climate changes that followed when the ice caps retreated, another is the spread of the human populations across the world that hunted these animals.

 We now know about 200 living species. It are mainly tree-dwelling animals. Their main characteristics are agility (great ability to move arms and legs, and a prehensile hand), intelligence, and parental care.

The origin of the big anthropoids is in the Miocene, in Africa. At the end of the Miocene they have swarmed out across Europe and Asia. .

Anthropoids that walk upright and can (thus) use their hands are called Hominids. The oldest known Hominid is Australopithecus, which originated in Africa about four million years ago. The first human was Homo habilis, which evolved from Australopithecus in the Early Pleistocene in Africa. Homo habilis, in turn, evolved into Homo erectus (‘upright man’) about 1.6 million years ago in Africa. As from one million years ago he is also found in other parts of the world. He reached China and Java 800,000 years ago, and Europe 500,000 years ago. The Homo erectus is the predecessor of the Homo sapiens, the modern man. One of the subspecies of Homo sapiens is the Neanderthal man, that lived from 200,000 to 30,000 years ago.

Our species, Homo sapiens sapiens, separated from Homo sapiens 100,000 years ago in Africa. Homo sapiens sapiens is the predecessor of all humans on earth. He also spread out across the continents, and under the influence of the local climate and conditions, several subspecies originated. One of these was the Cro-Magnon, that reached Europe 40,000 years ago. In the next 10,000 years, he displaced the Neanderthal. The Cro-Magnon is the predecessor of the Europeans.

The Holocene is the period that started after the last ice age. Humans start to use farming, and they learn how to manipulate ecosystems. In the stable communities that could live from agricultural products, a civilisation process was started that resulted in a fast-growing development of biological manipulation and technology. Humans first invented simple tools to improve agricultural techniques. Animals were domesticated and used to work the land and to provide food and clothes. The concentrations of social groups of humans also resulted in a bigger complexity of interaction, and the development of specialized tools within the community; skills that could then be ‘sold’ in exchange for other needs. The settlement of stable communities resulted in villages and cities, and ultimately in national states. From that moment on, the world population increased dramatically, and, in geological terms, the technological knowledge has progressed in a breath-taking speed. Humans are dominating the planet in an unequalled way.

 Homo sapiens sapiens.


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