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65-23Ma

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Paleogene Period

The Paleogene is a geologic period and system that began 66 and ended 23.03 million years ago and comprises the first part of the Cenozoic Era. Lasting 43 million years, the Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.

This period consists of the Paleocene, Eocene, and Oligocene Epochs. The end of the Paleocene (55.5/54.8 Mya) was marked by one of the most significant periods of global change during the Cenozoic, the Paleocene–Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals. The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary Period into two periods instead of directly into five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.

Of World Interest

It is estimated that ice began forming in Antarctica 34 million years ago. This caused the oceans to become less acidic. The data suggests that a fall in sea-level had the effect of leaving coral reefs stranded above the high-tide level where they were then eroded by wind and rain. Corals are composed of calcium carbonate - chalk - which has the effect of reducing acidity when dissolved in seawater.

Previous to this during the Eocene, our polar regions are believed to have had jungles.

Hominid Evolution

"We now dominate the planet, but we're here based on a historical contingency that occurred 34 million years ago. Our distant ancestors faced a climatic challenge 34 million years ago and, in Asia, our closest ancestors were not able to meet that challenge. Ultimately the Asian anthropoids went extinct." K. Christopher Beard

Because of a cooling and drying trend in the climate, primates went extinct in many parts of the world. Surviving primates clustered around equatorial Africa and Asia. If primates had survived the Eocene-Oligocene transition only in Asia, anthropoid evolution might have continued to limp along or might have died out entirely. But while lemur-like primates took over southern Asia, primates in Africa responded to the cooler temperatures of the Oligocene differently.

There, primate diversity shifted the other way. Many non-anthropoid primates went extinct, providing an ecological window for anthropoid "radiation," an evolutionary term referring to a burst of new species filling new ecological roles.

"All of the data that we have from the fossil record of primate evolution indicates that the very earliest anthropoids, the earliest members of this monkey, ape, and human group, actually originated in Asia, not in Africa. But we know by studying later chapters of this story that eventually the plot shifts from Asia to Africa."

Important Hominid Fossils

30 Ma (31 Ma) - DPC 2803 Aegyptopithecus zeuxis found 1965/66 in Egypt by Elwyn Simons

29–28 Ma - SGS-UM 2009-002 Saadanius hijazensis found 2010 in Shumaysi Formation, Saudi Arabia by Iyad S. Zalmout, et al.

47 Ma - Darwinius masillae, found in Germany. Length: About 2 feet (58 centimeters), including tail Closest living relatives: Primates, possibly the group including tarsiers, New and Old World monkeys, and great apes (including humans), Fingers and toes have nails instead of claws, Hind feet lack "grooming claws" seen in lemurs, Lacks "tooth comb" seen in lemurs and lorises, Ankle bone features may link it with the branch of primates leading to tarsiers, monkeys, and apes including humans, Opposable big toes, like nearly all primates

45 Ma - IVPP V11000 Eosimias sinensis, discovered in China in 1994 by K. Christopher Beard. It was found in a mountain near Liyang City, Jiangsu province, China. It is the earliest catarrhine that has been discovered

48.6 to 37.2 Ma - IVPP V11999 Eosimias dawsonae is the newest of the Eosimias species.The fossil includes a left dentary fragment and roots of the alveoli. It was collected by Christopher Beard in 1995

Paleogene Fauna

63 Mya - Dinosaurs go extinct

Mammals become abundant. The first primates appear. Flowering plants become abundant.

The Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a plethora of diverse animals in the wake of the mass extinction that ended the preceding Cretaceous Period. Some of these mammals would evolve into large forms that would dominate the land, while others would become capable of living in marine, specialized terrestrial and even airborne environments. Birds also evolved considerably during this period changing into roughly-modern forms. Most other branches of life on earth remained relatively unchanged in comparison to birds and mammals during this time period. Some continental motion took place. Climates cooled somewhat over the duration of the Paleogene and inland seas retreated from North America early in the Period.

An early primate, believed to be in the human evolutionary tree is Darwinius masillae, found in Germany and believed to be from 47 million years ago. Another fossil from China, Eosimias sinensis, dates to 45 Ma. Aegyptopithecus zeuxis, found in Egypt, dates to 31 Ma.

It is believed by some that an Eocene era fossil found in Germany, dubbed "Ida" is a "missing link" between higher primates such as monkeys, apes, and humans and their more distant relatives such as lemurs. Ida, known as Darwinius masillae, has a unique anatomy. The lemur-like skeleton features primate-like characteristics, including grasping hands, opposable thumbs, clawless digits with nails, and relatively short limbs. Scientists were able to examine fossil evidence of fur and soft tissue and even the remains of her last meal: fruits, seeds, and leaves.

Divisions

This period consists of the following epochs:

Paleocene 65 - 55 Mya

This epoch immediately followed the asteroid impact that presumably caused the extinction of the dinosaurs and the destruction of the Cretaceous world. This is known as a transitional period between the time of the dinosaurs and the emergence of the larger mammals of the Eocene. The early part of the period experienced cooler temperatures and a more arid climate than existed before the asteroid. But in the latter part of the epoch, the temperatures warmed significantly, resulting in the absence of glaciated poles and the presence of verdant, tropical forests. The warmer climate increased ocean temperatures leading to a proliferation of species such as coral and other invertebrates.

The Chicxulub crater on the the Yucatán Peninsula in Mexico is more than 180 km (110 mi) in diameter, making the feature one of the largest confirmed impact structures on Earth; the impacting bolide that formed the crater was at least 10 km (6 mi) in diameter.

The age of the rocks shows that this impact structure dates from the end of the Cretaceous Period, roughly 65 million years ago. The impact associated with the crater is implicated in causing the extinction of the dinosaurs as suggested by the Cretaceous–Paleogene boundary (K–Pg boundary) the geological boundary between the Cretaceous and Paleogene periods, although some critics argue that the impact was not the sole reason, and others debate whether there was a single impact or whether the Chicxulub impactor was one of several that may have struck the Earth at around the same time. Recent evidence suggests that the impactor may have been a piece of a much larger asteroid that broke up in a collision in distant space more than 160 million years ago.

In March 2010, following extensive analysis of the available evidence covering 20 years' worth of data spanning the fields of palaeontology, geochemistry, climate modelling, geophysics and sedimentology, 41 international experts from 33 institutions reviewed available evidence and concluded that the impact at Chicxulub triggered the mass extinctions at the K–Pg boundary including those of dinosaurs.

Effects

The impact would have caused some of the largest megatsunamis in Earth's history, reaching thousands of meters high. A cloud of super-heated dust, ash and steam would have spread from the crater, as the impactor burrowed underground in less than a second. Excavated material along with pieces of the impactor, ejected out of the atmosphere by the blast, would have been heated to incandescence upon re-entry, broiling the Earth's surface and possibly igniting global wildfires; meanwhile, colossal shock waves would have triggered global earthquakes and volcanic eruptions. The emission of dust and particles could have covered the entire surface of the Earth for several years, possibly a decade, creating a harsh environment for living things. The shock production of carbon dioxide caused by the destruction of carbonate rocks would have led to a sudden greenhouse effect. Over a longer period, sunlight would have been blocked from reaching the surface of the earth by the dust particles in the atmosphere, cooling the surface dramatically. Photosynthesis by plants would also have been interrupted, affecting the entire food chain. A model of the event developed by Lomax et al. (2001) suggests that net primary productivity (NPP) rates may have increased to higher than pre-impact levels over the long term because of the high carbon dioxide concentrations.

In February 2008, a team of researchers led by Sean Gulick at the University of Texas at Austin’s Jackson School of Geosciences used seismic images of the crater to determine that the impactor landed in deeper water than was previously assumed. They argued that this would have resulted in increased sulfate aerosols in the atmosphere. According to the press release, that "could have made the impact deadlier in two ways: by altering climate (sulfate aerosols in the upper atmosphere can have a cooling effect) and by generating acid rain (water vapor can help to flush the lower atmosphere of sulfate aerosols, causing acid rain).

Eocene 55 - 34 Mya

The Eocene saw an asteroid impact nearly as large as the Chicxulub impact. It was in Popigai, Siberia, Russia. It had a 100 km diameter and impacted 35 Million years ago.

The Paleocene-Eocene Thermal Maximum, timed at 55 million years ago, may have been caused by the clathrate gun effect, although potential alternative mechanisms have been identified. This was associated with rapid ocean acidification.

The warm temperatures of the early Eocene experienced a short-lived spike coinciding with the development of a more modern group of mammals, including animals with hooves, such as horses. The rise in temperature marks the appearance of Polecat Bench, (Wyoming's) horses and primates. Both poles were covered in temperate forests and oceans continued to be warm. "During the Eocene, the world north of the Arctic Circle was so warm that crocodiles flourished there. There were no ice caps, of course, and so much freshwater flowed into the Arctic Ocean that a layer of fresh­water sat like a lens over the salt water. The freshwater Azolla fern was plentiful. Forests of redwoods and walnut trees grew there. Pale­ontologists have found the remains of giant ants usually associated with the tropics."

The Arctic was a swamp about 53 million years ago and was home to a flightless bird, Gastornis with a head the size of a horse’s. The belief about Gastornis is based on a single toe bone found on Ellesmere Island back in the 1970s. But researchers say it’s a perfect match for toe bones from a bird known as Gastornis that lived in what's now North America around the same time period.

The epoch ended in a mass extinction on both the land and in the ocean, although the latter species suffered the most loss.

The primate ancestor of humans lost the ability for endogenous ascorbate production. This was the result of a mutation of the gene encoding for the enzyme L-gulono-glactone oxidase (GLO), a key enzyme in the conversion of glucose to ascorbate. As a result of this mutation all descendants became dependent on dietary ascorbate intake.

Bennett Lake Volcanic Complex in the Canadian Yukon Territory erupted about this time with approximately 850 km³ of ejecta. The Bennett Lake Volcanic Complex was formed when the ancient Kula Plate was subducting under North America during the early Eocene period. Cataclysmic eruptions from the Bennett Lake Volcanic Complex were from vents along arcuate fracture systems that spewed out about 850 km3 (200 cu mi) of glowing avalanches of pyroclastic rock called pyroclastic flows. Evacuation of the underlying magma chamber was followed by several stages of collapse to form two calderas, one nested inside the other, that produced an elliptical depression 19 km (12 mi) by 30 km (19 mi) across. The calderas were from 200 m (656 ft) to 2,700 m (8,858 ft) deep. Volcanism continued for some time after the caldera collapse. High level andesite and rhyolite dikes and intrusive bodies crosscut volcanic flows and tuffs at all levels. Dike swarms are emplaced along ring fractures and fault zones at the southwest edge of the caldera. Near the dying stages of the volcano, magma surged upward and arched the roof of the magma chamber into a broad dome with relief of about 1,500 m (4,921 ft).

Birds in Europe

"The pre-Oligocene European avifauna is characterized by the complete absence of passeriform birds, which today are the most diverse and abundant avian taxon. Representatives of small non-passeriform perching birds thus probably had similar ecological niches before the Oligocene to those filled by modern passerines. The occurrence of passerines towards the Lower Oligocene appears to have had a major impact on these birds, and the surviving crown-group members of many small arboreal Eocene taxa show highly specialized feeding strategies not found or rare in passeriform birds. It is detailed that no crown-group members of modern‘families’ are known from pre-Oligocene deposits of Europe, or anywhere else."

Note: Examples of nonpasseriform birds are: pigeons, woodpeckers, hummingbirds, and kingfishers, while passeriforms are perching birds, which make up the largest number of species of modern birds.

Oligocene 34 - 23 Mya

The cooling temperatures brought a return of the ice caps to the polar regions. The separation of Antactica from South America isolated the continent and surrounded it by cold ocean currents producing a glaciated continent. Whales appeared during the latter part of the epoch as other mammalian species continued to transition into modern forms.

The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic, a sudden global change, the Paleocene-Eocene Thermal Maximum, which upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.The Paleogene follows the Cretaceous Period and is followed by the Miocene Epoch of the Neogene Period. The terms 'Paleogene System' (formal) and 'lower Tertiary System' (informal) are applied to the rocks deposited during the 'Paleogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine subdivisions of time possible in the relatively recent geologic past, when more information is preserved. By dividing the Tertiary Period into two periods instead of five epochs, the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic Eras.

27.8 Mya La Garita Caldera was formed in Colorado, US with approximately 5,000 km³ of ejecta, often described as the largest known explosive eruption in Earth's history. The resulting deposit, known as the Fish Canyon tuff, has a volume of approximately 1,200 cubic miles (5,000 km3), enough material to fill Lake Michigan. By contrast, the most powerful human-made explosive device ever detonated, the Tsar Bomba or King of the Bombs, had a yield of 50 megatons, whereas the eruption at La Garita was about 5,000 times more powerful. It is one of the most energetic events on Earth since the Chicxulub impact, which was 400 times more powerful.

The formation of Madagascar.

It would be very easily perceived by looking at a map of today’s world that at some point in the history of plate tectonics, the island of Madagascar “broke away” from its apparently parental neighbouring continent of Africa. While this is not wholly untrue, it was the not the final cause of its isolation.

Although Madagascar was formed at the crossover between the Cretaceous and Paleogene periods, its breakup from the African continent occurred some 100 million years previous when they were both a part of the Gondwana supercontinent. Madagascar broke away from Africa as a part of the East Gondwana landmass which also contained India, Antarctica and Australia.

Ultimately Madagascar’s isolation was created when it broke away from the Indian subcontinent, which itself was landmass surrounded by water before it would later crash northwards into Asia violently creating the Himalaya mountain range from around 50 million years ago.

This relatively early isolation of one of today’s existing world islands has produced a typically unique biodiversity of life species.

One of the most famed animals of Madagascar is the lemur. The lemur is a primate, and primates did not emerge from the evolutionary tree until after the extinction of the dinosaurs. The death of these huge land dominating animals caused the survival of its sauropsid relatives to be declined to the lesser dominating individuals and therefore created a window for a flourishing evolution of mammalian life such as primates. The presence of primates on Madagascar is a great illustration of how recently Madagascar became an isolated island. The fact that lemurs are so unique and endemic to Madagascar is another great illustration of how long this large island has been isolated.

The formation of the Himalaya mountain range.

The Himalayas were formed in phases most likely from around 65 million years ago, although the Indian subcontinental landmass on the Indian plate did not have a hard impact against the Asian landmass until around 25 million years ago. What this means is that even though India as an island was still apparently travelling northwards along the Indian Ocean, the Himalayas had started to form because the tectonic plate was already reacting with the Eurasian plate.

Firstly the sea bed was raised and folded into ridges and valleys by the soft impact between the two plates before the continued pressure pushed this rock up to create mountains around 50 million years ago. The relentless northward journey of the Indian plate connected the two landmasses and continued to lift the mountains ever higher, even creating a weather anomaly protecting the Indian subcontinent from the Arctic winds of the north.

Even to this day the Indian plate shifts northwards and pushes the peaks higher.

Nummulites and their influence on Ancient Egypt.

40 million years ago, the world’s landmasses were still configuring themselves into their current positions. The tectonic plate of north east Africa had not yet closed against the Anatolian landmass, therefore water from the Atlantic Ocean had a free route directly to the Indian Ocean via the waterway that would become the Mediterranean Sea. Many but not all of today’s lands between modern day Greece and modern day Pakistan, the gap that was to be closed, was in fact underwater.

One of those lands was northern modern day Egypt. A notable area of Egypt and indeed Arabia was submerged around the northern part of today’s Red Sea. Within this body of water a type of creature emerged on the sea bed that had a hard shell. This creature is called a nummulite.

The significance of nummulites is that their shells (abundant in calcium and carbon) became used as Ancient Egyptian coins. The limestone of the Nile Valley was rich in fossilised nummulites and it was this limestone that was used to construct the famous pyramid tomb monuments of Egypt.

Sources

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