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The Age of Mammals

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Setting the Stage The Cenozoic follows the Cretaceous (K-T) extinction that caused dinosaurs to go extinct. The planet was dominated by relatively small mammals, birds, reptiles, and amphibians. It did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. Some birds grew larger than the average human. This group became known as the "terror birds," and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals.

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Arrangement of Continents At the beginning of the Cenozoic, most of continents had separated into their present form. Australia had yet to separate from Antarctica and India had yet to collide with Asia.

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Geology of the Cenozoic During the Cenozoic, the continents move into their current positions. Australia-New Guinea, having split from Pangaea during the early Cretaceous, drifted north and, eventually, collided with South-east Asia Antarctica moved into its current position over the South Pole 65 million years ago 35 million years ago 50 million years ago

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Geology of the Cenozoic The Atlantic Ocean widened and, later in the era, South America became attached to North America via the isthmus of Panama. India collided with Asia 55 to 45 mya and created the Himalayan Mountains. Arabia collided with Eurasia, closing the Tethys ocean, around 35 mya. 20 million years ago Present day 50 thousand years ago

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Cenozoic Video https://www.youtube.com/watch?v=ApsCGttW2Us (Age of Mammals - Global Processes 3:11) https://www.youtube.com/watch?v=ApsCGttW2Us

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Estimated Global Temperatures in the Cenozoic Eon

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Cenozoic Climate Trends Climate trends are closely related to the geological map. The PaleoceneEocene Thermal Maximum (PETM) of 55.8 mya was a significant global warming event However, since the Azolla event of 49 mya, the Cenozoic Era has been a period of long-term cooling. After the tectonic creation of Drake Passage, when South America fully detached from Antarctica during the Oligocene (a geologic epoch of the Paleogene period and extends from about 33.9 to 23 mya), the climate cooled significantly due to the advent of the Antarctic Circumpolar Current which brought cool deep Antarctic water to the surface.

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Cenozoic Climate Trends The cooling trend continued in the Miocene, with relatively short warmer periods. When South America became attached to North America creating the Isthmus of Panama, the Arctic region cooled due to the strengthening of the Humboldt and Gulf Stream currents, eventually leading to the glaciations of the Quaternary ice age, the current interglacial of which is the Holocene Epoch.

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Renaming the Tertiary Tertiary is the former term for the geologic period from 66 million to 2.58 million years ago, a time span that lies between the unused Primary period (Proterozoic) and Secondary period (Paleozoic) and the Quaternary. The Tertiary is no longer recognized as a formal unit by the International Commission on Stratigraphy, but the word is still widely used. The Tertiary has been divided between the Paleogene and Neogene Periods and the first stage of the Pleistocene epoch.

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Paleogene The Paleogene (informally Lower Tertiary) 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 K-T extinction event that ended the preceding Cretaceous Period. Time 66 - 23 million years ago (Cenozoic Era)

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Paleogene Geology The continents during the Paleogene continued to drift closer to their current positions. India was in the process of colliding with Asia, subsequently forming the Himalayas. The Atlantic Ocean continued to widen and Africa was moving north to meet with Europe and form the Mediterranean South America was moving closer to North America (they would later connect via the Isthmus of Panama). Inland seas retreated from North America early in the period. Australia had also separated from Antarctica and was drifting towards Southeast Asia. Mean atmospheric O2 content over period duration ca. 26 Vol % (130 % of modern level) Mean atmospheric CO2 content over period duration ca. 500 ppm (2 times pre- industrial level) Mean surface temperature over period duration ca. 18 C (4 C above modern level)

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Paleogene Climate Early in the Cenozoic, the Paleocene-Eocene Thermal Maximum (PETM) occurred - this period of global warming was due to methyl hydrates being released from marine sediments. With the exception of the PETM, a cooling and drying trend (relative to the Mesozoic) occurred throughout the Paleogene, a trend that persists today. The trend was partly caused by the formation of the Antarctic Circumpolar Current, which significantly cooled oceanic water temperatures.

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Paleogene Climate The major changes in the oceanic and atmospheric circulation and led to the extinction of numerous marine life and a major turnover in mammals. Modern rain forests and grasslands appeared. Grasses, an angiosperm, evolved in the Paleogene promoting the evolution of a variety of large grass-eating herbivores like horses, cattle, deer, etc.

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Paleogene Biology Mammals began to take advantage of the niches left empty by the extinction of the dinosaurs, evolving into many new species. However, mammals were not the dominant predators in the early Paleogene - a group of terror birds, large flightless birds are found in the fossil record. Prosimians, insectivorous early relatives of true primates can be found. The largest mammal, Pantolambda (a primitive plant eater), was about the size of a small pony. Rodents appeared late in the Paleocene epoch of the Paleogene.

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Paleogene Biology Although the majority of Cretaceous plant species did not survive into the Paleocene, ferns were very abundant for a brief period following the end- Cretaceous asteroid impact. Subsequently, flowering plants and conifers once again became more abundant during the early Paleocene. The marine world of the Paleocene was much more like the modern marine realm than that of the Cretaceous. Sharks ruled in the absence of Mesozoic marine predatory reptiles The cooling trend meant that polar ice caps developed as well as tropical forests and grasslands. Temperate forests with seasons produced the mixed deciduous forest we see today. Cooling temperature produced vast grasslands which supported large grazing herbivores.

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Paleogene Megafauna This period produced very large birds, the largest land mammals ever seen on the planet (Paraceratherium, see below), the evolution of whales, massive snakes (Titanoboa), and large predators.

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Neogene The Neogene covers about 20 million years. During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids, the ancestors of humans, appeared in Africa. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows. Time 23 - 2.3 m.y.a (Cenozoic Era)

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Neogene Geology Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama. This cut off the warm ocean currents from the Pacific to the Atlantic ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean.

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Neogene Geology The Neogene Period was a time when the continents were crashing into each other. Mountains pushed up in many places. India continued its push into Asia further raising the Himalayan Mountain Range. Italy moved north into Europe raising the Alps. Spain crashed into France to form the Pyrenees. The Rocky Mountains and the Andes Mountains formed in North and South America during this time.

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Neogene Sea levels Sea levels were lower due to the effects of cooling temperatures and continental collision. The North and South Poles began to have ice caps. During the Neogene Period, the polar ice thickened and took up more space in the ocean. The new mountains trapped water as snow and ice. All of this ice formation caused sea levels to drop even more. The drop in sea levels opened up land bridges between continents. This allowed animals to migrate between continents.

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Neogene Geology Summary The continents in the Neogene were very close to their current positions. The isthmus of Panama formed, connecting North and South America. The Andes began to rise. India continued to collide with Asia, forming the Himalayas. Sea levels fell, exposing land bridges between Africa and Eurasia and between Eurasia and North America. The global climate became seasonal and continued its overall drying and cooling trend which began in the beginning of the Paleogene. The ice caps on both poles began to grow and thicken, and by the end of the period the first of a series of glaciations of the current Ice Age began. Mean atmospheric O2 content over period duration ca. 21.5 Vol % (108 % of modern level) Mean atmospheric CO2 content over period duration ca. 280 ppm (1 times pre- industrial level) Mean surface temperature over period duration ca. 14 C (0 C above modern level)

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Neogene Biology In response to the cooler, seasonal climate, tropical plant species gave way to deciduous ones and grasslands replaced many forests. Grasses therefore greatly diversified, and herbivorous mammals evolved alongside it, creating the many grazing animals of today such as horses, antelope, and bison.

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Neogene Biology South America moved to the north. By the Pliocene Epoch it merged with North America forming the Isthmus of Panama. Armadillos, porcupines, ground sloths and opossums migrated from South America to North America. Dogs, cats, bears, and horses from North America crossed into South America.

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Neogene Biology The climate continued to cool. Many of the areas that had been covered by forests were changing to grasslands. Grasses were better suited to the cool dry weather. But grasses had less nutrition than the forest plants of the Paleogene Period. It took more effort to get the nutrients out. Grasses were made of chemicals that were hard on teeth. Chewing wore the teeth down. Animals that ate grasses needed stronger teeth. Other animals developed new ways to digest the grasses inside their bodies. These animals had more than one stomach. They are called ruminants. They were efficient at getting nutrients from the grasses. This new type of animal, the artiodactyl, developed into many familiar species: camels, bison, sheep and giraffes, to name a few. The grazing animals could run fast. Predators had to adapt or go hungry. The sleek bodies of the dog and cat carnivores were able to run fast and use their powerful jaws and teeth to take down their prey.

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Neogene Megafauna & Extinction The Megafauna (meg-UH-fawn-UH) or "big animals" were the large animals that lived during the late Cenozoic Era after the extinction of the dinosaurs, mostly during the last Ice Age. They included animals such as the Woolly Mammoth, Smilodon (sabre-toothed cat), Megatherium (Giant ground sloth) and other large herbivores Most were very large and often hairy, having a long, thick, mammoth-like fur coat covering nearly their entire bodies to protect themselves from the cold. They all went extinct in the geological blink of an eye around 10,000 years ago for reasons not quite known. Some suspect it was early man, which appear in the fossil record when the Megafauna started to go extinct. https://www.youtube.com/watch?v=iaCIkiZLK ig (Extinction of the Smilodon) https://www.youtube.com/watch?v=iaCIkiZLK ig

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Quaternary The term Quaternary ("fourth") was proposed in 1759 for alluvial deposits in northern Italy. It was introduced in 1829 for sediments of France's Seine Basin that seemed clearly to be younger than Tertiary Period rocks. The Quaternary Period follows the Neogene Period and extends to the present. The Quaternary covers the time span of glaciations classified as the Pleistocene, and includes the present interglacial period, the Holocene. This places the start of the Quaternary at the onset of Northern Hemisphere glaciation approximately 2.6 million years ago. Prior to 2009, the Pleistocene was defined to be from 1.805 million years ago to the present, so the current definition of the Pleistocene includes a portion of what was, prior to 2009, defined as the Pliocene. Time 2.6 million years ago to the present (Cenozoic Era)

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Quaternary Time 2.3 million years ago to the present (Cenozoic Era) Subdivisions of the Quaternary System System/ Period Series/ Epoch Stage/ Age Age (Ma) Quaternary Holocene0.0117-0 Pleistocene Tarantian0.126-0.0117 Ionian0.781-0.126 Calabrian1.80-0.781 Gelasian2.58-1.80 NeogenePliocenePiacenzianolder

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Quaternary Geology The 2.6 million years of the Quaternary represents the time during which recognizable humans existed. Over this short time period, there has been relatively little change in the distribution of the continents due to plate tectonics. The Quaternary geological record is preserved in greater detail than that for earlier periods. The major geographical changes during this time period included the emergence of the Strait of Bosphorus and Skagerrak during glacial epochs, which respectively turned the Black Sea and Baltic Sea into fresh water, followed by their flooding (and return to salt water) by rising sea level The periodic filling of the English Channel, forming a land bridge between Britain and the European mainland The periodic closing of the Bering Strait, forming the land bridge between Asia and North America.

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Quaternary Climate The climate was one of periodic glaciations with continental glaciers moving as far from the poles as 40 degrees latitude. During this time, substantial glaciers advanced and retreated over much of North America and Europe, parts of South America and Asia, and all of Antarctica. The Great Lakes formed and giant mammals thrived in parts of North America and Eurasia not covered in ice. Artist's impression of Earth during the Last Glacial Maximum

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Quaternary Biology During the Quaternary period, mammals, flowering plants, and insects dominated the land. There was a major extinction of large mammals in Northern areas at the end of the Pleistocene Epoch. Many forms such as saber-toothed cats, mammoths, mastodons, glyptodonts, etc., became extinct worldwide. Others, including horses, camels and American cheetahs became extinct in North America. These mammals became extinct when the glacial period Age ended about 11,700 years ago. This extinction coincides with the arrival of humans into North America from Asia. Modern humans evolved about 190,000 years ago Northern Hemisphere Ice Age during the Quaternary.

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The Holocene The Holocene is the name of the epoch that we live in today. It started 11,700 years ago with the end of the last glaciation. Climatologists believe we are living in an interglacial period that will end with onset of a new ice age. There have been minor warm and cool periods in the Holocene. The impact of modern industrial society is affecting the atmosphere and may have an impact on the climate in the future. Pre-industrial CO2 levels were about 230 ppm, today we have exceeded 400 ppm.

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Cenozoic Videos https://www.youtube.com/watch?v=eObjVCFv-IM (The North American Ice Age : Documentary on How Ice Created North America (44:07)) https://www.youtube.com/watch?v=eObjVCFv-IM https://www.youtube.com/watch?v=eY-ltUIsnrQn (The 6 th extinction) (9:17) https://www.youtube.com/watch?v=eY-ltUIsnrQn https://www.youtube.com/watch?v=7QY-FY9nz-M (The Holocene Extinction) https://www.youtube.com/watch?v=7QY-FY9nz-M