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Description

The Cenozoic Era is the third era of the Phanerozoic Eon, following the Mesozoic Era. This is the current geological time era and began about 66 million years ago, continuing to this day. The Cenozoic is divided into seven epochs. The first two epochs are the Paleocene and Eocene; the Paleocene lasting from 66 to 56 mya and the Eocene lasting from 56 to 34 mya.

Shortly after the K/T extinction event that wiped out 75% of all living things, including the non-avian dinosaurs, Earth's began to recover. The climate of the early Paleocene was cooler and drier than the earlier Cretaceous, but by the beginning of the Eocene global temperatures rose sharply to an average of over 8 degrees Celsius warmer than today. This caused tropical conditions to expand far beyond the equator to the point that lush rainforests had spread all over the planet from the Arctic to Antarctica by the start of the Eocene. Fossils of trees such as cypress, palms, and redwoods have been found as far North as Alaska and Greenland. The continents moving slowly into the positions we see them in today as they had begin to do during the Cretaceous. North America was still connected with Asia as Europe was with Greenland. Africa was moving northward towards Europe, closing the Tethys sea that had long separated Laurasia and Gondwana. India started moving north as well, on a slow collision course with the Eurasian tectonic plate. By the end of the Eocene these two plates collided, forcing up the crust of the Earth into what would become the largest and tallest mountain range on Earth; the Himalayas.

Despite the enormous loss of life at the end of the Cretaceous, there were enough survivors to repopulate Earth's biosphere after being ravaged by the K/T extinction. These survivors included a handful of mammals, birds(the only dinosaurs not driven to extinction), reptiles, amphibians, fish, sharks, insects and other invertebrates. Nearly every animal on dry land that remained had one thing in common; they were all small. No terrestrial creatures larger than around 55 pounds survived the extinction. Among them the birds and mammals showed the most extreme changes in the millions of years after the extinction, with both groups quickly diversifying into many different families to fill the void left behind by animals like the dinosaurs and marine reptiles. As forests spread during the Paleocene mammals grew larger and adopted more body plans and niches than their Mesozoic ancestors ever could. These first large mammals included predators and plant eaters. Throughout the Paleocene and early Eocene several groups of strange mammals sprung up; groups not related to any living mammals, such as flat-footed herbivorous pantodonts, large rhino-like uintatheres, and wolf-like hoofed carnivorous mesonychids. Birds took on many new forms as well, with the largest bird being the six foot tall flightless Gastornis of Europe and North America. After the intense
rise in temperature during the Eocene, the larger, earlier mammal groups became less common while newer groups of smaller mammals rose in abundance. These groups included the ancestors of most major modern families including the earliest bats, rodents, camels, pigs, anteaters, rhinos, horses, carnivores, tapirs, hedgehogs, proboscedians(elephant-ancestors) and primates. The very first whales emerged as well from small hoofed animals in the same group as many ungulates, including hippos and pigs. While being terrestrial hunters at first, these animals gradually became more and more aquatic until their feet and legs became flippers, their tails grew flukes, and their noses became blowholes. Reptiles flourished just as well as the mammals and birds in the hot, lush climate of a new world, although the surviving groups of snakes, lizards, crocodilians and other groups never reached the same size and ecological importance of the dinosaurs they outlived or the new groups of mammals. Still some species of lizards, snakes and turtles reached great sizes in many parts of the world, In the seas numerous fish groups survived, and sharks regained their position as the oceans top predators with the giant marine reptiles gone. By the late Eocene, however, several species of predatory whales had evolved to grow large enough to hunt sharks and take over the seas.

The mid-Eocene, roughly 40 million years ago, saw a remarkable change in global climate. For the first time in hundreds of millions of years, Antarctica began to freeze. Its lush jungles turned into temperate forests and tundra as a great ice cap formed and started to grow. This caused Earth's climate to start getting cooler and drier. The late Eocene was still quite warm, but the interiors of the continents became much drier and much of the vast forests disappeared. New open environments gave many of the smaller groups of mammals an invitation to grew larger and and more adapted to running as the horses, camels, rhinos, and many carnivores began to do. The trends in global cooling and drying and in mammals growing larger and faster would continue for most of the rest of the Cenozoic era. The changes in climate and habitat lead many groups into extinction at the end of the Eocene, especially as ocean communities were disrupted. Among mammals most of the earlier whales died out, paving the way for modern toothed and baleen whales to evolve, while on land many earlier browsing mammals who could not feed on tough dry-climate plants died out or became less common.

†Presbyornis pervetus: birds got a bit of a head start ahead of the mammals after the Mesozoic ended as many modern groups of birds had already appeared before all the non-avian dinosaurs went extinct. Among them were the ancestors of ostriches, plovers, owls, penguins, parrots, pheasants, chickens and ducks. Presybornis was a member of the same family that the ducks and geese would evolve from. It resembled a duck or goose in much of its morphology with a long neck and a broad, flat bill. Its body was about as big as a large swan, but it walked on very long, flamingo-like legs. Fossils from Europe and North America show it gathered in large flocks around shallow lakes much like modern flamingos. Their bills would have been sued like a dabbling duck to filter small plants and animals from the water.

†Barylambda faberi: Barylambda was a member of the first family of large herbivorous mammals to evolve. Known as pantodonts these beasts were slowing moving and dim-witted compared to later kinds of mammal. Barylambda had robust limbs and walked flat on its feet like a bear, had a thick, muscular tail, short tusks in the males, and a small brain compared to its body size. As big as a horse it was one of the largest animals in the first Paleocene and Eocene rainforests of North America.

†Uintatherium anceps: uintatheres were the biggest herbivores of the early Eocene forests, similar in shape to rhinos but only very distant cousins of living ungulates. Uintatherium weighed about two tons and was 13 feet long, one of the biggest of its kind. Its strangest features were the three pairs of short knob-shaped horns on top of the skull; similar to giraffes, and a pair of long saber-tooth-like tusks found in both males and females, shielded by bony protrusions of the lower jaw. As herbivores these tusks, as well as the horns, were probably used for fighting rivals for mates and territory. By the mid-Eocene as open habitats began to replace forests, uintatheres became rare and eventually replaced by giant relatives of rhinos.

†Mesonyx uintensis: these wolf-like carnivores were one of the first types of larger mammalian predators and were common during the Paleocene and early Eocene but died out shortly after the Eocene. Mesonyx was a genus from North America and Asia and was about as big as a med-sized wolf of today and shaped like one too. It had a large sagital crest on the skull that supported powerful jaw muscles. Oddly though, its toes were covered in hooves instead of bearing claws. Mesonyx was in fact a cousin of the two groups of living hoof mammals, more closely related to deer, pigs and goats than to wolves and dogs.

†Eohippus angustidens: horses first appeared at the start of the Eocene as many modern groups of mammals first did. While some families would remain unchanged for millions of years, the first horses like Eohippus of North America would have a long way to go before they resembled the equines we are familiar with. Having evolved in a world covered in dense rainforests, Eohippus was small and short legged, weighing about 30 pounds and standing as tall as a cat. Instead of one big hoof as in modern horses, Eohippus walked on four small hooves on its front feet and three on its hind feet. It probably scurried across the forest floor away from larger predators, feeding on soft leaves and fallen fruit.

†Oxyaena lupina: after the mesonychids evolved, creodonts appeared and became an important group of predators. Different species resembled different types of modern carnivores, but these were not closely related to any living carnivore like dogs or cats. Oxyaena was a species from North America that appeared in the Paleocene. It had a cat-like body and grew about as big as a clouded leopard. It walked flat on its paws instead of on its toes, and it was likely a skilled tree climber while its short limbs probably made it a poorer runner. It had a broad, low skull with powerful lower jaws giving it a strong bite, but its brain was quite smaller than many predators today.

†Notharctus tenebrosus: this was one of the earliest primates from the Eocene. Found in North America it seemed to closely resemble lemurs; which it was close too, although the first lemurs had already colonized the island of Madagascar 55 million years ago. Like lemurs Notharctus had a long bushy tail and a longer snout than more derived primates. Its hands and feet were already adapted to grasping with opposable digits and nails instead of claws. Forward-facing eyes gave Notharctus keen vision. Like many lemurs and other more primitive primates these animals were likely nocturnal for the most part; sleeping during the day and leaping from tree to tree in search of leaves and fruits.

†Gastornis gigantea: Gastornis was the biggest bird of the Paleocene/Eocene, standing taller than a man. Flightless like an ostrich it had massive legs, short wings, a long muscular neck and a massive head and beak. This bird was once believed to have been the Eocene forests top predator, using its huge beak to snap small mammal's spines in half. However, due to the fact that these beak, though very strong, had no hooked edge, its claws were blunt, and its legs were not built for chasing prey through a thick forest. Today Gastornis is believed to have been mostly herbivorous, using its strong beak to bite through hard seeds and tough vegetation. Its closest living relatives are believed to be ducks and geese.

†Zygorhiza kochi: basilosaurid whales were the first group of large whales fully adapted to life in the oceans. Zygorhiza of the late Eocene of North America had a fluked tail, strong foreflippers and a tiny pair of hind-flippers where the backlegs once were. These legs were almost useless for the whales, although some believe they helped the whales cling-together when they mated in the water. Whales like Zygorhiza had more elongated bodies than modern whales and dolphins. The warm Eocene seas did not require a store of blubber to keep warm, and they also lacked the bulbous forehead of most modern cetaceans. But with long jaws, sharp teeth and agile bodies, Zygorhiza and its kind were ferocious aquatic hunters, feeding on fish, squid, sharks and even smaller whale species.

†Titanomyra gigantea: this ant from the Eocene of Europe was the largest ant of all time. Queen ants of this species were as big as hummingbirds. Worker ants of this species may have marched through the forest in mighty armies like driver ants today. With powerful jaws these ants could have swarmed and overpowered potentially large prey such as small birds and mammals.

†Megacerops coloradensis: as the climate became drier during the Eocene and forests started to thin out, many mammal groups took the opportunity to expand both in range and in size. Brontotheres like Megacerops were close relatives of horses, tapirs and rhinos, which also began to grow in size and diversity as open plains started to spread. the brontotheres, however, quickly conquered the plains and grew into giant herbivores that roamed the Northern Hemisphere in massive herds. Megacerops was as big as a modern forest elephant weighing over three tons and standing over 8 feet tall at the shoulder hump. It and many other species sported large, strange branched horns on their snouts. Megacerops horn was strong enough to inflict damage on one another as many fossils show impact injuries on the ribs. Males horns were slightly bigger than females, supported the case that males used them in conflicts over mates and dominance in a herd. Both sexes would have fought off predators with these horns too. After the Eocene Megacerops and other brontotheres became extinct as tougher vegetation replaced the softer plants they preferred to eat and other grazers like true rhinos replaced them.

†Barbaturex morrisoni: reptiles continued to thrive after the extinction of the dinosaurs as the world became lush and tropical. Barbaturex was a plant-eating lizard from the late Eocene of Myanmar around 37 mya. Jaw fossils show it had short spikes lining the lower jaw. This lizard grew to great size, up to six feet long including the massive tail. Among a community of small ungulates and carnivorous mammals, Barbaturex must have been an important member of its ecosystem.

Description

The Cenozoic Era is the third era of the Phanerozoic Eon, following the Mesozoic Era. This is the current geological time era and began about 66 million years ago, continuing to this day. The Cenozoic is divided into seven epochs. The first two epochs are the Paleocene and Eocene; the Paleocene lasting from 66 to 56 mya and the Eocene lasting from 56 to 34 mya.

Shortly after the K/T extinction event that wiped out 75% of all living things, including the non-avian dinosaurs, Earth's began to recover. The climate of the early Paleocene was cooler and drier than the earlier Cretaceous, but by the beginning of the Eocene global temperatures rose sharply to an average of over 8 degrees Celsius warmer than today. This caused tropical conditions to expand far beyond the equator to the point that lush rainforests had spread all over the planet from the Arctic to Antarctica by the start of the Eocene. Fossils of trees such as cypress, palms, and redwoods have been found as far North as Alaska and Greenland. The continents moving slowly into the positions we see them in today as they had begin to do during the Cretaceous. North America was still connected with Asia as Europe was with Greenland. Africa was moving northward towards Europe, closing the Tethys sea that had long separated Laurasia and Gondwana. India started moving north as well, on a slow collision course with the Eurasian tectonic plate. By the end of the Eocene these two plates collided, forcing up the crust of the Earth into what would become the largest and tallest mountain range on Earth; the Himalayas.

Despite the enormous loss of life at the end of the Cretaceous, there were enough survivors to repopulate Earth's biosphere after being ravaged by the K/T extinction. These survivors included a handful of mammals, birds(the only dinosaurs not driven to extinction), reptiles, amphibians, fish, sharks, insects and other invertebrates. Nearly every animal on dry land that remained had one thing in common; they were all small. No terrestrial creatures larger than around 55 pounds survived the extinction. Among them the birds and mammals showed the most extreme changes in the millions of years after the extinction, with both groups quickly diversifying into many different families to fill the void left behind by animals like the dinosaurs and marine reptiles. As forests spread during the Paleocene mammals grew larger and adopted more body plans and niches than their Mesozoic ancestors ever could. These first large mammals included predators and plant eaters. Throughout the Paleocene and early Eocene several groups of strange mammals sprung up; groups not related to any living mammals, such as flat-footed herbivorous pantodonts, large rhino-like uintatheres, and wolf-like hoofed carnivorous mesonychids. Birds took on many new forms as well, with the largest bird being the six foot tall flightless Gastornis of Europe and North America. After the intense
rise in temperature during the Eocene, the larger, earlier mammal groups became less common while newer groups of smaller mammals rose in abundance. These groups included the ancestors of most major modern families including the earliest bats, rodents, camels, pigs, anteaters, rhinos, horses, carnivores, tapirs, hedgehogs, proboscedians(elephant-ancestors) and primates. The very first whales emerged as well from small hoofed animals in the same group as many ungulates, including hippos and pigs. While being terrestrial hunters at first, these animals gradually became more and more aquatic until their feet and legs became flippers, their tails grew flukes, and their noses became blowholes. Reptiles flourished just as well as the mammals and birds in the hot, lush climate of a new world, although the surviving groups of snakes, lizards, crocodilians and other groups never reached the same size and ecological importance of the dinosaurs they outlived or the new groups of mammals. Still some species of lizards, snakes and turtles reached great sizes in many parts of the world, In the seas numerous fish groups survived, and sharks regained their position as the oceans top predators with the giant marine reptiles gone. By the late Eocene, however, several species of predatory whales had evolved to grow large enough to hunt sharks and take over the seas.

The mid-Eocene, roughly 40 million years ago, saw a remarkable change in global climate. For the first time in hundreds of millions of years, Antarctica began to freeze. Its lush jungles turned into temperate forests and tundra as a great ice cap formed and started to grow. This caused Earth's climate to start getting cooler and drier. The late Eocene was still quite warm, but the interiors of the continents became much drier and much of the vast forests disappeared. New open environments gave many of the smaller groups of mammals an invitation to grew larger and and more adapted to running as the horses, camels, rhinos, and many carnivores began to do. The trends in global cooling and drying and in mammals growing larger and faster would continue for most of the rest of the Cenozoic era. The changes in climate and habitat lead many groups into extinction at the end of the Eocene, especially as ocean communities were disrupted. Among mammals most of the earlier whales died out, paving the way for modern toothed and baleen whales to evolve, while on land many earlier browsing mammals who could not feed on tough dry-climate plants died out or became less common.

†Presbyornis pervetus: birds got a bit of a head start ahead of the mammals after the Mesozoic ended as many modern groups of birds had already appeared before all the non-avian dinosaurs went extinct. Among them were the ancestors of ostriches, plovers, owls, penguins, parrots, pheasants, chickens and ducks. Presybornis was a member of the same family that the ducks and geese would evolve from. It resembled a duck or goose in much of its morphology with a long neck and a broad, flat bill. Its body was about as big as a large swan, but it walked on very long, flamingo-like legs. Fossils from Europe and North America show it gathered in large flocks around shallow lakes much like modern flamingos. Their bills would have been sued like a dabbling duck to filter small plants and animals from the water.

†Barylambda faberi: Barylambda was a member of the first family of large herbivorous mammals to evolve. Known as pantodonts these beasts were slowing moving and dim-witted compared to later kinds of mammal. Barylambda had robust limbs and walked flat on its feet like a bear, had a thick, muscular tail, short tusks in the males, and a small brain compared to its body size. As big as a horse it was one of the largest animals in the first Paleocene and Eocene rainforests of North America.

†Uintatherium anceps: uintatheres were the biggest herbivores of the early Eocene forests, similar in shape to rhinos but only very distant cousins of living ungulates. Uintatherium weighed about two tons and was 13 feet long, one of the biggest of its kind. Its strangest features were the three pairs of short knob-shaped horns on top of the skull; similar to giraffes, and a pair of long saber-tooth-like tusks found in both males and females, shielded by bony protrusions of the lower jaw. As herbivores these tusks, as well as the horns, were probably used for fighting rivals for mates and territory. By the mid-Eocene as open habitats began to replace forests, uintatheres became rare and eventually replaced by giant relatives of rhinos.

†Mesonyx uintensis: these wolf-like carnivores were one of the first types of larger mammalian predators and were common during the Paleocene and early Eocene but died out shortly after the Eocene. Mesonyx was a genus from North America and Asia and was about as big as a med-sized wolf of today and shaped like one too. It had a large sagital crest on the skull that supported powerful jaw muscles. Oddly though, its toes were covered in hooves instead of bearing claws. Mesonyx was in fact a cousin of the two groups of living hoof mammals, more closely related to deer, pigs and goats than to wolves and dogs.

†Eohippus angustidens: horses first appeared at the start of the Eocene as many modern groups of mammals first did. While some families would remain unchanged for millions of years, the first horses like Eohippus of North America would have a long way to go before they resembled the equines we are familiar with. Having evolved in a world covered in dense rainforests, Eohippus was small and short legged, weighing about 30 pounds and standing as tall as a cat. Instead of one big hoof as in modern horses, Eohippus walked on four small hooves on its front feet and three on its hind feet. It probably scurried across the forest floor away from larger predators, feeding on soft leaves and fallen fruit.

†Oxyaena lupina: after the mesonychids evolved, creodonts appeared and became an important group of predators. Different species resembled different types of modern carnivores, but these were not closely related to any living carnivore like dogs or cats. Oxyaena was a species from North America that appeared in the Paleocene. It had a cat-like body and grew about as big as a clouded leopard. It walked flat on its paws instead of on its toes, and it was likely a skilled tree climber while its short limbs probably made it a poorer runner. It had a broad, low skull with powerful lower jaws giving it a strong bite, but its brain was quite smaller than many predators today.

†Notharctus tenebrosus: this was one of the earliest primates from the Eocene. Found in North America it seemed to closely resemble lemurs; which it was close too, although the first lemurs had already colonized the island of Madagascar 55 million years ago. Like lemurs Notharctus had a long bushy tail and a longer snout than more derived primates. Its hands and feet were already adapted to grasping with opposable digits and nails instead of claws. Forward-facing eyes gave Notharctus keen vision. Like many lemurs and other more primitive primates these animals were likely nocturnal for the most part; sleeping during the day and leaping from tree to tree in search of leaves and fruits.

†Gastornis gigantea: Gastornis was the biggest bird of the Paleocene/Eocene, standing taller than a man. Flightless like an ostrich it had massive legs, short wings, a long muscular neck and a massive head and beak. This bird was once believed to have been the Eocene forests top predator, using its huge beak to snap small mammal's spines in half. However, due to the fact that these beak, though very strong, had no hooked edge, its claws were blunt, and its legs were not built for chasing prey through a thick forest. Today Gastornis is believed to have been mostly herbivorous, using its strong beak to bite through hard seeds and tough vegetation. Its closest living relatives are believed to be ducks and geese.

†Zygorhiza kochi: basilosaurid whales were the first group of large whales fully adapted to life in the oceans. Zygorhiza of the late Eocene of North America had a fluked tail, strong foreflippers and a tiny pair of hind-flippers where the backlegs once were. These legs were almost useless for the whales, although some believe they helped the whales cling-together when they mated in the water. Whales like Zygorhiza had more elongated bodies than modern whales and dolphins. The warm Eocene seas did not require a store of blubber to keep warm, and they also lacked the bulbous forehead of most modern cetaceans. But with long jaws, sharp teeth and agile bodies, Zygorhiza and its kind were ferocious aquatic hunters, feeding on fish, squid, sharks and even smaller whale species.

†Titanomyra gigantea: this ant from the Eocene of Europe was the largest ant of all time. Queen ants of this species were as big as hummingbirds. Worker ants of this species may have marched through the forest in mighty armies like driver ants today. With powerful jaws these ants could have swarmed and overpowered potentially large prey such as small birds and mammals.

†Megacerops coloradensis: as the climate became drier during the Eocene and forests started to thin out, many mammal groups took the opportunity to expand both in range and in size. Brontotheres like Megacerops were close relatives of horses, tapirs and rhinos, which also began to grow in size and diversity as open plains started to spread. the brontotheres, however, quickly conquered the plains and grew into giant herbivores that roamed the Northern Hemisphere in massive herds. Megacerops was as big as a modern forest elephant weighing over three tons and standing over 8 feet tall at the shoulder hump. It and many other species sported large, strange branched horns on their snouts. Megacerops horn was strong enough to inflict damage on one another as many fossils show impact injuries on the ribs. Males horns were slightly bigger than females, supported the case that males used them in conflicts over mates and dominance in a herd. Both sexes would have fought off predators with these horns too. After the Eocene Megacerops and other brontotheres became extinct as tougher vegetation replaced the softer plants they preferred to eat and other grazers like true rhinos replaced them.

†Barbaturex morrisoni: reptiles continued to thrive after the extinction of the dinosaurs as the world became lush and tropical. Barbaturex was a plant-eating lizard from the late Eocene of Myanmar around 37 mya. Jaw fossils show it had short spikes lining the lower jaw. This lizard grew to great size, up to six feet long including the massive tail. Among a community of small ungulates and carnivorous mammals, Barbaturex must have been an important member of its ecosystem.