23-2 Ma

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§ Neogene Period

This period includes the Miocene (23.03 to 5.332 Ma), and Pliocene, the second epoch of the Neogene, which extends from 5.332 million to 1.806 million years before present.

The Neogene traditionally ended at the end of the Pliocene epoch, just before the older definition of the beginning of the Quaternary Period; many time scales show this division. However, there is a movement amongst geologists (particularly Neogene Marine Geologists) to also include ongoing geological time (Quaternary) in the Neogene, while others (particularly Quaternary Terrestrial Geologists) insist the Quaternary to be a separate period of distinctly different record. The somewhat confusing terminology and disagreement amongst geologists on where to draw what hierarchical boundaries, is due to the comparatively fine divisibility of time units as time approaches the present, and due to geological preservation that causes the youngest sedimentary geological record to be preserved over a much larger area and reflecting many more environments, than the slightly older geological record. By dividing the Cenozoic era into three (arguably two) periods (Paleogene, Neogene, Quaternary) instead of 7 epochs, the periods are more closely comparable to the duration of periods in the Mesozoic and Paleozoic eras.

The Neogene covers roughly 23 million years. During the Neogene mammals and birds evolved considerably. Most other forms were relatively unchanged. Some continental motion took place, the most significant event being the connection of North and South America in the late Pliocene. Climates cooled somewhat over the duration of the Neogene culminating in continental glaciations in the Quaternary sub-era (or period, in some time scales) that follows, and that saw the dawn of the genus Homo.

During the beginning of the Neogene, climates remained moderately warm, although the slow global cooling that eventually led to the Pleistocene glaciations continued. Mountain building took place in Western North America and Europe. Both continental and marine Miocene deposits are common worldwide with marine outcrops common near modern shorelines. Well studied continental exposures occur in the American Great Plains and in Argentina. India continued to collide with Asia, creating more mountain ranges. The Tethys Seaway continued to shrink and then disappeared as Africa collided with Eurasia in the Turkish-Arabian region between 19 and 12 mya. Subsequent uplift of mountains in the western Mediterranean region and a global fall in sea levels combined to cause a temporary drying up of the Mediterranean Sea (known as the Messinian salinity crisis) near the end of the Miocene.

Although a long-term cooling trend was well underway, there is evidence of a warm period during the Miocene when the global climate rivaled that of the Oligocene. The Miocene warming began 21 million years ago and continued until 14 million years ago, when global temperatures took a sharp drop - the Middle Miocene Climate Transition (MMCT). By 8 million years ago, temperatures dropped sharply once again, and the Antarctic ice sheet was already approaching its present-day size and thickness. Greenland may have begun to have large glaciers as early as 7 to 8 million years ago, although the climate for the most part remained warm enough to support forests there well into the Pliocene.

During the Miocene, grasslands underwent a major expansion as forests fell victim to a generally cooler and drier climate overall. Grasses also diversified greatly into different species and also caused a major increase in the biodiversity of large herbivores and grazers, including ruminants.

Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist. Mammals were also modern, with recognizable wolves, raccoons, horses, beaver, deer, camels, and whales.

Recognizable crows, ducks, auks, grouses and owls appear in the Miocene. By the epoch's end, all or almost all modern families are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved instead of too equivocal in character. Marine birds reached their highest diversity ever in the course of this epoch.

Brown algae plants, called kelp, proliferate, supporting new species of sea life, including otters, fish and various invertebrates. The cetaceans diversified, and some modern genera appeared, such as the sperm whales. The pinnipeds, which appeared near the end of the Oligocene, became more aquatic.

Perhaps most important were the 100 or so species of apes that lived during this time. They occupied much of the Old World and ranged in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominoid clade, but molecular evidence indicates this ape lived from between 15 to 12 million years ago.

In the second epoch of the Hologene, the change to a cooler, dry, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species world-wide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry savannahs, deserts appeared in Asia and Africa.

In North America, rodents, large mastodonts and gomphotheres, and opossums continued successfully, while hoofed animals (ungulates) declined, with camel, deer and horse all seeing populations recede. Rhinos, tapirs and chalicotheres went extinct. Carnivores including the weasel family diversifed, and dogs and fast-running hunting bears did well. Ground sloths, huge glyptodonts and armadillos came north with the formation of the Isthmus of Panama.

In Eurasia rodents did well, while primate distribution declined. Elephants, gomphotheres and stegodonts were successful in Asia, and hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinos did fairly well. Cows and antelopes were successful, and some camel species crossed into Asia from North America. Hyaenas and early saber-toothed cats appeared, joining other predators including dogs, bears and weasels. Human evolution during the Pliocene

Africa was dominated by hoofed animals, and primates continued their evolution, with australopithecines (some of the first hominids) appearing in the late Pliocene. Rodents were successful, and elephant populations increased. Cows and antelopes continued diversification and overtaking pigs in numbers of species. Early giraffes appeared, and camels migrated via Asia from North America. Horses and modern rhinos came onto the scene. Bears, dogs and weasels (originally from North America) joined cats, hyaenas and civets as the African predators, forcing hyaenas to adapt as specialized scavengers.

South America was invaded by North American species for the first time since the Cretaceous, with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates, South American natives, did well. Small weasel-like carnivorous mustelids and coatis migrated from the north. Grazing glyptodonts, browsing giant ground sloths and smaller armadillos did well.

The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos, and the huge diprotodonts. Carnivorous marsupials continued hunting in the Pliocene, including dasyurids, the dog-like thylacine and cat-like Thylacoleo. The first rodents arrived, while bats did well, as did ocean-going whales. The modern platypus, a monotreme, appeared.

The predatory phorusrhacids were rare in this time; among the last was Titanis, a large phorusrhacid that rivaled mammals as top predators. Its distinct featured was it claws, which was re-evolved for grasping prey, such as Hipparion. Other birds probably evolved at this time, some are modern, some are now extinct.

Alligators and crocodiles died out in Europe as the climate cooled. Venomous snakes genera continued to increase as more rodents and birds evolved. Oceans continued to be relatively warm during the Pliocene, though they continued cooling. The Arctic ice cap formed, drying the climate and increasing cool shallow currents in the North Atlantic. Deep cold currents flowed from the Antarctic.

The formation of the Isthmus of Panama about 3.5 million years ago cut off the final remnant of what was once essentially a circum-equatorial current that had existed since the Cretaceous and the early Cenozoic. This may have contributed to further cooling of the oceans worldwide.

The Pliocene seas were alive with sea cows, seals and sea lions.

§Arctic

3 million year ago the Arctic was dotted with forests. Sea levels were 80 feet (24 meters) higher than they are currently. The average temperate was about 2 degrees C warmer than today. CO2 levels were about 400 parts for every million parts of air in the mid-Pliocene compared to 383.1 parts per million in 2007. The causes of the ancient warming are not completely understood. They are believed to be a combination of increased greenhouse gases from natural sources and a greater impact by ocean currents in moving warm water to cold regions.

§ Africa

It is believed that early hominoids emerged in this era.

  • 21 Ma A fossil of a creature called Morotopithecus bishopi, a tree-dwelling, ape-like creature that lived in what is now Uganda, was found in the 1960s and indicated that its transverse process had moved backward, behind the opening for the spinal cord. In 2007 Dr. Aaron Filler authored "The Upright Ape: a new origin of the Species," in which he argued that this common ancestor, and ancestors going back many millions of years before, walked upright. Homo sapiens, the human species, continued upright, while apes evolved back toward all fours.
  • 20 Ma The gorilla lineage evolved from a common ancestor of orangutans about this time.
  • 18 Ma Proconsul africanus fossil found by Mary Leakey
  • 12 Ma Gorilla and chimpanzees split from a common ancestor about this time.
  • 10 Ma In 2007 Ethiopian fossil hunter found molars of a large ape that bespoke gorilla origins from about this time. They named the large ape Chororapithecus abyssinicus.
  • 9.8 - Kenya - In 2007 Researchers in Kenya unveiled a 10-million-year-old jaw bone they believe belonged to a new species of great ape that could be the last common ancestor of gorillas, chimpanzees and humans. A Kenyan and Japanese team found the fragment, dating back to between 9.8 and 9.88 million years, in 2005 along with 11 teeth. The fossils were unearthed in volcanic mud flow deposits in the northern Nakali region of Kenya.
  • 9 Ma - The first creatures in the human lineage lived about this time.
  • 6 Ma Kenya - Orrorin tugenensis ("millenium man") nicknamed millenium man because fossils were found in the year 2000.
  • 5.5 Ma to 4 Ma - Ethiopia - Ardipithecus ramidus
  • 4.4 Ma A partial skeleton in more than 90 pieces was found by a group led by Tim White, Gen Suwa and Berhane Asfaw in the Middle Awash at Aramis, Ethiopia, in late 1994. They name it Ardipithecus ramidus, which put it in a new genus and means ground ape root. A new argon-argon dating technique was used.
  • Australopithecus anamensis discovery occurred in the Kanapoi region of East Lake Turkana in 1965
  • 3.5 Ma - Kenyanthropus Lake Turkana Kenya, possible direct human ancestor.
  • 3.4 Ma - First evidence of tool use. The journal Nature reports that newly discovered tool marks on bones indicates that we were using tools at minimum 800,000 years earlier than previously thought. This places the start of tool use at 3.4 million years ago or earlier. The most likely ancestor in this time frame would be Australopithecus afarensis.
  • 3 Ma - Teeth of Australopithecus africanus analyzed from this period indicate consumption of large quantities of carbon 13 from either grasses and sedges of animals that ate such plants or both. This was a transition period of movement from trees and forests to more open land.
  • 3.4 Ma - Ethiopia - Australopithecus Afarensis represented in the earliest find at Hadar in 1974 in the skeleton nicknamed, "Lucy" and again in 2006 by a juvenile, perhaps aged 3, nicknamed "Dikika Girl" found in the Dikika region of Ethiopia. It's believed that these small hominins walked upright, but had strong shoulder "ape-like" blades and long arms adapted for tree climbing and swinging.
  • 2.7 Ma - Australopithecus aethiopicus ("Black Skull") Omo deposits, north of Lake Turkana.
  • 2.5 Ma - Australopithecus garhi, Hatayae Member of the Bouri Formation, Ethiopia
  • 2.3 Ma - primitive stone tools were first used to scavenge kills made by other predators, and harvest carrion for their bones and marrow. In hunting, Homo habilis was probably not capable of competing with large predators, and was still more prey than hunter, although Homo habilis probably did steal eggs from nests, and may have been able to catch small game, and weakened larger prey (cubs and older animals). The tools were classed as Oldowan.
  • 2 Ma - South Africa - Prof. Raymond Dart in 1924 after his analysis of the Taung child skull from a cave South Africa. Average age of sample teeth is 22 years at death, as analyzed by Alan Mann. In 2006 new analysis of the Taung skull suggested that the child was killed by a predatory bird.
  • 2.3 Ma Australopithecus boisei (an older find) from Omo, Ethiopia.
  • 2.3 Ma to 1 Ma - Ethiopia - Homo habilis Homo habilis is the first hominoid to bear the distinction of being classified as Homo. Homo habilis had a larger brain and a more varied diet that, for the first time, included meat. Homo habilis ("Man the tool maker") was named thusly because of evidence of early tool creation, stone choppers and other stone tools. These may have been used to crack open bones to access the marrow.

§ China

Archaelogical evidence suggests that Homo erectus lived in China from the period beginning 2.24 billion years ago.

§North America

Titanis walleri, also "Terror Birds", a species of very large predatory flightless bird, lived approximately 5-1.8 million years ago (Pliocene) in North America, fossil evidence having been found in Florida and Texas.

§South Pacific

§Hawaii

The islands of Kauai and Niihau date back to 5 million years ago. The entire chain is older, but these are the oldest of the existing main islands.

§Space

In 2002, astronomers discovered that roughly 2 million years ago, around the end of the Pliocene epoch, a group of bright O and B stars called the Scorpius-Centaurus OB association passed within 150 light-years of Earth and that one or more supernovae may have occurred in this group at that time. Such a close explosion could have damaged the Earth's ozone layer and caused the extinction of some ocean life (consider that at its peak, a supernova of this size could produce that same amount of absolute magnitude as an entire galaxy of 200 billion stars).

§ Sources

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