Modern life-forms continued to diversify and inhabit the land, the sky, and the oceans. Whales, dolphins, and manatees evolved in marine habitats.
Amphibians, lizards, crocodilians, snakes, early deer, antelope, pronghorns, and horses also evolved in the Tertiary Period. The first elephant-like mammals appeared, as did dogs cats, pigs, and weasels. The notable event in the Quaternary Period were the ice ages that began 2 Million Years ago and remained until 10, Years Ago.
The Jurassic period , from about million to million years ago, ushered in birds and mammals. And the Cretaceous period , from million to 66 million years ago is known for its iconic dinosaurs, such as Triceratops , and pterosaurs such as Pteranodon. Coniferous plants, or those that have cone-bearing seeds, already existed at the beginning of the era, but they became much more abundant during the Mesozoic.
Flowering plants emerged during the late Cretaceous period. The lush plant life during the Mesozoic era provided plenty of food, allowing the biggest of the dinosaurs , such as the Argentinosaurus , to grow up to 80 tons, according to a study in the journal Revista del Museo Argentino de Ciencias Naturales.
Earth during the Mesozoic era was much warmer than today, and the planet had no polar ice caps. During the Triassic period, Pangaea still formed one massive supercontinent. Without much coastline to moderate the continent's interior temperature, Pangaea experienced major temperature swings and was covered in large swaths of desert. Yet the region still had a belt of tropical rainforest in regions around the equator, said Brendan Murphy, an earth scientist at St.
Francis Xavier University in Antigonish, Canada. The Mesozoic era was bookended by two great extinctions, with another smaller extinction occurring at the end of the Triassic period, Olsen said. Fossils of these very fragile plants are rare. The oldest known bryophytes lived on wet mudflats during the early Devonian, but it is likely that they colonised the land during the late Silurian.
Vascular plants, which emerged during the late Silurian, resemble green algae from which they evolved. Cooksonia was the first to evolve. It was a small plant 6 cm high that lacked leaves, but had spherical spore sacs at the ends of its branched stems.
A little later, Zosterophllophytina the ancestor of the clubmosses and Rhyniophytina ancestral to leaf-bearing Trimerophytina and all the other vascular plants we see today appeared. During the Carboniferous, many new groups of plants evolved and great forests grew in the tropical swamps and deltas.
Trees were not like those we know today, but mainly clubmosses and horsetails, and the earliest gymnosperms seed-bearing plants like conifers and seed ferns also developed. Conifers grew mainly on the high ground and are rarely fossilised, although cones are occasionally found. Seed ferns, the only major plant group to have become extinct, were usually small, but Medullosa grew to about five metres tall.
Pecopteris , a fern from the Carboniferous. The first forests were the great tropical coal forests of the late Carboniferous million years ago : tree-sized horsetails Calamites 6 , club-mosses Lepidodendron 7 , tree-ferns Psaronius 8 , and the seed ferns Medullosa 9 , rise above an undergrowth of ferns, seed ferns, herbaceous horsetails, like Sphenophyllum 10 , and clubmosses.
Giant Carboniferous dragonflies and amphibians inhabit the forests. The Carboniferous seed fern Neuropteris belonged to a group of plants that became extinct in the Cretaceous. Gymnosperms dominated the plant kingdom during the Jurassic and Cretaceous. Conifers continued to thrive and cycads and ginkgos spread throughout the world. By the Jurassic, cycads and cycad-like plants cycadeoids were abundant and widespread.
Some cycadeoids had what look like flowers, but these were in fact petal-like scales for seed dispersal rather than pollination. Ginkgos, or maidenhairs, grew throughout the northern hemisphere until the end of the Cretaceous, when they began to disappear, so that only a single species, in the forests of western China, is left today. Wealden woodlands: Mesozoic plants in an early Cretaceous landscape million years ago : conifers Pseudofrenolopsis 11 , cycads Nilssonia 12 , cycad-like plants Otozamites 13 and Pseudocycas 14 , and tree ferns Tempskya 15 abound.
Small ferns like Weichselia 16 form the undergrowth. Horsetails Equisetites 17 , non-vascular liverworts Hepaticites 18 and clubmosses Selaginellites 19 grow in the wetter areas. The herbiverous dinosaur Iguanadon feeds on the Wealden plants. He undertook experiments designed to find out how lightning - simulated by repeated electrical discharges - might have affected the primitive earth atmosphere.
He discharged an electric spark into a mixture thought to resemble the primordial composition of the atmosphere. In a water receptacle, designed to model an ancient ocean, amino acids appeared. Amino acids are widely regarded as the building blocks of life.
Although the primitive atmosphere is no longer believed to be as rich in hydrogen as was once thought, the discovery that the Murchison meteorite contains the same amino acids obtained by Miller, and even in the same relative proportions, strongly suggests that his results are relevant. It may seem surprising that bacteria can leave fossils at all.
However, one particular group of bacteria, the cyanobacteria or "blue-green algae," have left a fossil record that extends far back into the Precambrian - the oldest cyanobacteria-like fossils known are nearly million years old and are among the oldest fossils currently known. Cyanobacteria are larger than most bacteria, and many secrete a thick cell wall. More importantly, cyanobacteria may form large layered structures, called stromatolites more or less dome-shaped or oncolites round.
These structures form as a mat of cyanobacteria growths in a marine environment, trapping sediment and sometimes secreting calcium carbonate. When sectioned very thinly, fossil stromatolites may be found to contain exquisitely preserved fossil cyanobacteria and algae.
These early cells belonged to the group of prokaryotic cells in contrast to the more complex structures of eukaryotic cells. Prokaryotes are small cells which lack the complex internal structures, like mitochondria and chloroplasts, found in eukaryotic cells. Although prokaryotes possess DNA on a chromosome, it is not enclosed in a nucleus. The first algae - million years ago - The Proterozoic Era m. The final Era of the Precambrian, the Proterozoic Era, spans the time between million and million years ago.
Fossils of both primitive single celled and more advanced multicellular organisms begin to appear in abundance in rocks from this era. The name, proterozoic, means "early life.
The oldest multi-cellular algae fossil dates to million years. At this time biological diversity increased greatly to become eukaryote cells. Different to the prokaryotic cells, the eukaryotic cells are larger and have a complex internal organisation and which includes a nucleus housing the DNA on the chromosomes and specialised structures known as organelles.
The oldest fossil evidence of multi-cellular animals, or metazoans, are burrows which suggest they were made by smooth, wormlike creatures. Theses fossils have been found in rocks in various places including China, Canada, India.
The imprints of these soft bodied animals reveal little else but their basic shape. Oxygen must have been freely available by the time the first eukaryotic cells arrived, released through the proliferation of cyanobacteria, earlier in the Precambrian. The Vendian animals - million years ago - The Vendian Period m. The first animals in the fossil record appeared between and million years ago. This period is called the Vendian after the stratigraphic sequence in Russia where rocks of this age are especially well developed.
The Vendian period is also known as the Ediacaran period after a site in Australia and is distinguished by a characteristic collection of fossils from complex soft-bodied animals. These fossils have been found at several localities around the world. There are two confusing aspects of the Vendian or Ediacaran organisms: firstly there does not seem to be any evidence for any skeletal hard parts, in any of those fossils, i.
Secondly, is the issue of which group of animals these group of fossils belong to. Although many have been compared to modern day jelly fish or worms they have been also compared to be somewhat like analogous to a 'mattress' with tough outer walls and fluid filled internal cavities, something like a sponge. However, Simon Conway Morris, of Cambridge University, argued them to be higher developed animals than sponges, as there were no sponge fossils in the Vendian fauna.
Sponges are regarded as quite primitive animals and should have appeared before the Vendian soft bodied organisms. The earliest period of the Palaeozoic era is called the Cambrian Period.
It is named after Cambria, the Roman name for Wales, where rocks of this age were first identified by the nineteenth century geologist Adam Sedgwick. Cambrian sediments, however, are by no means restricted to Wales but found in many other parts of the world.
As recently as the middle of last century the earliest known fossils had all come from the Cambrian. The Cambrian fossils include animals with body plans similar to those of a number of living animals and they represent the lineages of almost all animals living today.
This stunning and unique evolutionary flowering is termed the "Cambrian explosion". But it was not as rapid as an explosion: the changes seem to have happened during about 30 million years, and some stages took 5 to 10 million years.
The emergence of many kinds of creatures during the transition from the Precambrian to the Cambrian radically changed the nature of the relations among animals, including the development of more complex predator-prey relationships.
Animals that fed on living matter, rather than scavenging on dead organic matter or relying on symbiotic relationships with photosynthesising algae, became much more common and even predators, such as Anomalocaris , evolved to eat those who could not escape them.
Laid down in the middle-Cambrian, when the "explosion" had already been underway for several million years, this formation contains the first appearance in the fossil record of brachiopods , with clamlike shells, as well as trilobites , molluscs , echinoderms , and many odd animals that probably belong to extinct phyla.
The cause of the Cambrian "explosion" is a matter of debate among scientists. Some point to the increase in oxygen that began around million years ago supporting a higher metabolic rate and allowing the evolution of larger organisms and more complex body structures. Others propose that an extinction of life at the end of the Vendian period opened up ecological roles that the new forms exploited. A change in ocean chemistry may have occurred, allowing for the first time the development of hard body parts such as teeth and supporting skeletons.
Genetic factors were also crucial. Recent research suggests that the period prior to the Cambrian explosion saw the gradual evolution of a "genetic tool kit" of genes the homeobox or "hox" genes that govern developmental processes.
Once assembled, this genetic tool kit enabled an unprecedented period of evolutionary experimentation -- and competition. Many forms seen in the fossil record of the Cambrian disappeared without trace.
Future evolutionary change was then limited to acting on the body plans that remained in existence. Recently many scientists have begun to question whether the Cambrian explosion was a real event, or a reflection of the patchiness of this ancient fossil record. Genetic data suggest that multicellular animals evolved around million years ago; this is supported by fossil embryos from rocks in China that date back million years.
In addition, trilobites were a very diverse group even early in the Cambrian, and some scientists suggest that this indicates that the arthropod group must have had a much earlier evolutionary origin. During the Cambrian, evolution was rapid and within a few million years the Earth was populated with many animal groups.
Fossils found elsewhere indicate that the marine ancestors of New Zealand's ancient land dwelling caterpillar-like Peripatus were alive at that time. Cambrian deposits in the Cobb Valley, in north-west Nelson of the South Island are the oldest accurately dated geological formations in New Zealand. Some associated sequences occur in small areas in the southwest of Fiordland.
The fauna typically consist of Trilobites, Brachiopods, Sponges and Ostracods. Be aware that the rocks in the Cobb Valley are protected and specimens cannot be removed.
The Rise of the fish - The Ordovician Period m. The time between and million years ago is called the Ordovician. It is named after a Celtic tribe called the Ordovices. At this time, the area north of the tropics was almost entirely ocean, and most of the world's land was collected into the southern super-continent Gondwana.
Throughout the Ordovician, Gondwana shifted towards the South Pole and much of it was submerged underwater. During the Ordovician the first plants appeared. But it was not until the late Silurian before they resembled modern plants. It is widely assumed that the first eukaryotic cells were non-photosynthetic descendants of Archaebacteria.
The theory of endosymbiosis proposes that mitochondria and chloroplasts were derived from symbiotic, aerobic Eubacteria, and were engulfed by ancestral eukaryotic cells. The Ordovician is best known for the presence of its diverse marine invertebrates, including graptolites , trilobites , brachiopods , and the conodonts early vertebrates.
A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. A burst of evolution went on to triple the diversity of marine animal life in the space of 50 million years.
Fish are members of the chordate phylum because they display certain defining characteristics: a backbone that replaces the notochord of the 'simpler' chordates, a dorsal nerve, gills and a tail. Agnathans, or jawless fish were the earliest fish and the first true vertebrates and they appeared around million years ago.
One of the Agnathan lineages were the Ostracoderms, the earliest jawless fish, dating back around million years. They were bottom-feeders and were almost entirely covered in armour plates. As jaws evolve in the bony fish and early sharks around million years, jawless fish had trouble competing. Hagfish and lampreys are the only jawless fish alive today. While sharks are not plentiful until the Devonian period to million years ago , their fossil scales date the existence of the earliest sharks to the late Ordovician.
With these new groups of Palaeozoic fauna the ocean ecology reorganised and the new species adapted to use resources more efficiently. After the reorganisation of changing lifestyles, species lasted longer and extinction occurred less frequently than among the Cambrian ancestors. From the Early to Middle Ordovician, the Earth experienced a milder climate in which the weather was warm and the atmosphere contained a lot of moisture.
However, when Gondwana finally settled on the South Pole during the Late Ordovician, massive glaciers formed causing shallow seas to drain and sea levels to drop. It has been estimated that at least 70 percent of oceanic species became extinct at the end of the Ordovician period, in what may have been the second largest of all mass extinctions.
Compare this with several mass extinctions which culled early animals during the 50 million years of the Cambrian but from which they bounced back to their previous levels. All life on Earth was still in the sea.
The sediments that were to become New Zealand formed a shallow sea shelf off the coast of Gondwana. Well defined Ordovician rocks, characterised by Graptolite faunas can be found in the Nelson region and the south west of Fiordland. Venturing on land - the Silurian Period m. The Silurian period, named after a Celtic tribe called the Silures, was the time when some plants and animals left the water and colonized the land for the first time.
Why they left the water is still being debated but it was probably the result of competition in the marine ecosystems, escaping predators and the availability of new land-based environments. Once animals and plants became established on land they contributed to changes in the nature of the physical and chemical processes on Earth. But living on land required new strategies for survival, such as obtaining nutrients and water, avoiding desiccation, carrying out gas exchange, and reproduction.
Early vascular land plants - so named for their internal system of tubing that circulates water and nutrients - evolved around million years ago. Most grew only a few centimetres tall but were still tall enough to send shoots skyward to capture sunlight and release reproductive spores to the winds.
With deeper root systems than earlier plants rhizoids , not true roots and a rigid vertical stem, they were now equipped to colonise more of the Earth's surface. An example for one of the simple vascular plants is Cooksonia. Arthropods were the first animals to adapt to the land, appearing there around about million years ago.
Fossil arthropod footprints of arthropods from western Australia, that were made in the sandy flats surrounding temporary lakes, indicate that these animals may have accompanied the landward march of plants.
In most ways they were pre-adapted to life on land. By the time they moved ashore, they had already evolved lighter bodies and spindly but strong legs to counteract the force of gravity.
Their hard outer shells, called cuticles, provided protection and retained moisture. Spiders, centipedes and mites were among the earliest land variants. Some of them were the giants of their joint-legged kind.
The longest kind of its species was Slimonia , a relative of the scorpions, which was the size of a man. This animal was still too big and too heavy and the walking legs too small to venture onto land and probably lived in marginal marine deltaic environments. As marine creatures began to adapt to changing temperatures and salinity, they were preparing themselves for life on land.
At Hailes Knob, to the west of Motueka, a few Silurian fossils such as shellfish and trilobites have been found. There is a boulder by the roadside before the entrance to the Takaka Gorge, in the Cobb Valley, Nelson, which shows folds of marble and sandstone.
It is possible to see a few tiny shellfish and crinoid stems in this rock. Invasion of the land - the Devonian Period m. The Devonian period was named after Devonshire, England, where rocks of this age were first studied. During the Devonian, early arthropods and vertebrates continued to colonise the land. The animals had to solve the same problems that plants faced when they moved to the land, such as reducing water loss and maximising oxygen uptake. The evolutionary advances that solved these problems not only allowed animals to invade land, but also to radiate over the continents.
During the Devonian, there were three major continental masses: North America and Europe sat together near the equator with much of their current land underneath the seas. To the north lay a portion of modern Siberia. During the Devonian, two major animal groups dominated the land. The first tetrapods , or land-living vertebrates , appeared during the Devonian, as did the first terrestrial arthropods, including wingless insects and the earliest arachnids which had already ventured onto land during the Silurian.
In the oceans, brachiopods flourished. One of the first amphibians was Ichthyostega , which lived during the late Devonian in what is now Greenland.
Its skull was nearly identical to that of the fish Eusthenopteron and it also retained a deep tail with fins. Ichthyostega had four strong limbs and its head was clearly separated from its body by a neck.
0コメント