The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are uncertain; the name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich. The Oligocene is followed by the Miocene Epoch; the Oligocene is the final epoch of the Paleogene Period. The Oligocene is considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included a global expansion of grasslands, a regression of tropical broad leaf forests to the equatorial belt; the start of the Oligocene is marked by a notable extinction event called the Grande Coupure. By contrast, the Oligocene–Miocene boundary is not set at an identified worldwide event but rather at regional boundaries between the warmer late Oligocene and the cooler Miocene.
Oligocene faunal stages from youngest to oldest are: The Paleogene Period general temperature decline is interrupted by an Oligocene 7-million-year stepwise climate change. A deeper 8.2 °C, 400,000-year temperature depression leads the 2 °C, seven-million-year stepwise climate change 33.5 Ma. The stepwise climate change began 32.5 Ma and lasted through to 25.5 Ma, as depicted in the PaleoTemps chart. The Oligocene climate change was a global increase in ice volume and a 55 m decrease in sea level with a related temperature depression; the 7-million-year depression abruptly terminated within 1–2 million years of the La Garita Caldera eruption at 28–26 Ma. A deep 400,000-year glaciated Oligocene Miocene boundary event is recorded at McMurdo Sound and King George Island. During this epoch, the continents continued to drift toward their present positions. Antarctica became more isolated and developed an ice cap. Mountain building in western North America continued, the Alps started to rise in Europe as the African plate continued to push north into the Eurasian plate, isolating the remnants of the Tethys Sea.
A brief marine incursion marks the early Oligocene in Europe. Marine fossils from the Oligocene are rare in North America. There appears to have been a land bridge in the early Oligocene between North America and Europe, since the faunas of the two regions are similar. Sometime during the Oligocene, South America was detached from Antarctica and drifted north towards North America, it allowed the Antarctic Circumpolar Current to flow cooling the Antarctic continent. Angiosperms continued their expansion throughout the world as tropical and sub-tropical forests were replaced by temperate deciduous forests. Open plains and deserts became more common and grasses expanded from their water-bank habitat in the Eocene moving out into open tracts; however at the end of the period, grass was not quite common enough for modern savannas. In North America, subtropical species dominated with cashews and lychee trees present, temperate trees such as roses and pines were common; the legumes spread, while sedges and ferns continued their ascent.
More open landscapes allowed animals to grow to larger sizes than they had earlier in the Paleocene epoch 30 million years earlier. Marine faunas became modern, as did terrestrial vertebrate fauna on the northern continents; this was more as a result of older forms dying out than as a result of more modern forms evolving. Many groups, such as equids, rhinos and camelids, became more able to run during this time, adapting to the plains that were spreading as the Eocene rainforests receded; the first felid, originated in Asia during the late Oligocene and spread to Europe. South America was isolated from the other continents and evolved a quite distinct fauna during the Oligocene; the South American continent became home to strange animals such as pyrotheres and astrapotheres, as well as litopterns and notoungulates. Sebecosuchians, terror birds, carnivorous metatheres, like the borhyaenids remained the dominant predators. Brontotheres died out in the Earliest Oligocene, creodonts died out outside Africa and the Middle East at the end of the period.
Multituberculates, an ancient lineage of primitive mammals that originated back in the Jurassic became extinct in the Oligocene, aside from the gondwanatheres. The Oligocene was home to a wide variety of strange mammals. A good example of this would be the White River Fauna of central North America, which were a semiarid prairie home to many different types of endemic mammals, including entelodonts like Archaeotherium, running rhinoceratoids, three-toed equids, nimravids and early canids like Hesperocyon. Merycoidodonts, an endemic American group, were diverse during this time. In Asia during the Oligocene, a group of running rhinoceratoids gave rise to the indricotheres, like Paraceratherium, which were the largest land mammals to walk the Earth; the marine animals of Oligocene oceans resembled today's fauna, such as the bivalves. Calcareous cirratulids appeared in the Oligocene; the fossil record of marine mammals is a little spotty during this time, not as well known as the Eocene o
Orthopristis is a genus of grunts native to the Atlantic and Pacific coasts of the Americas. The recognized species in this genus are: Orthopristis cantharinus Orthopristis chalceus Orthopristis chrysoptera Orthopristis forbesi D. S. Jordan & Starks, 1897 Orthopristis lethopristis D. S. Jordan & Fesler, 1889 Orthopristis reddingi D. S. Jordan & R. E. Richardson, 1895 Orthopristis ruber
Anisotremus is a genus of grunts native to the eastern Pacific and western Atlantic Oceans. The recognized species in this genus are: Anisotremus caesius Anisotremus davidsonii Anisotremus dovii Anisotremus interruptus Anisotremus moricandi Anisotremus pacifici Anisotremus scapularis Anisotremus surinamensis Anisotremus taeniatus T. N. Gill, 1861 Anisotremus virginicus
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
Perciformes called the Percomorpha or Acanthopteri, is an order or superorder of ray-finned fish. If considered a single order, they are the most numerous order of vertebrates, containing about 41% of all bony fish. Perciformes means "perch-like"; this group comprises over 10,000 species found in all aquatic ecosystems. The order contains about 160 families, the most of any order within the vertebrates, it is the most variably sized order of vertebrates, ranging from the 7-mm Schindleria brevipinguis to the 5-m marlin in the genus Makaira. They first diversified in the Late Cretaceous. Among the well-known members of this group are perch and darters, sea bass and groupers; the dorsal and anal fins are divided into anterior spiny and posterior soft-rayed portions, which may be or separated. The pelvic fins have one spine and up to five soft rays, positioned unusually far forward under the chin or under the belly. Scales are ctenoid, although sometimes they are cycloid or otherwise modified. Classification is controversial.
As traditionally defined before the introduction of cladistics, the Perciformes are certainly paraphyletic. Other orders that should be included as suborders are the Scorpaeniformes, Tetraodontiformes, Pleuronectiformes. Of the presently recognized suborders, several may be paraphyletic, as well; these are grouped by suborder/superfamily following the text Fishes of the World. Photos of Perciformes on Sealife Collection
The Paleocene or Palaeocene, the "old recent", is a geological epoch that lasted from about 66 to 56 million years ago. It is the first epoch of the Paleogene Period in the modern Cenozoic Era; as with many geologic periods, the strata that define the epoch's beginning and end are well identified, but the exact ages remain uncertain. The Paleocene Epoch is bracketed by two major events in Earth's history, it started with the mass extinction event at the end of the Cretaceous, known as the Cretaceous–Paleogene boundary. This was a time marked by the demise of non-avian dinosaurs, giant marine reptiles and much other fauna and flora; the die-off of the dinosaurs left unfilled ecological niches worldwide. The Paleocene ended with the Paleocene–Eocene Thermal Maximum, a geologically brief interval characterized by extreme changes in climate and carbon cycling; the name "Paleocene" comes from Ancient Greek and refers to the "old" "new" fauna that arose during the epoch. The K–Pg boundary that marks the separation between Cretaceous and Paleocene is visible in the geological record of much of the Earth by a discontinuity in the fossil fauna and high iridium levels.
There is fossil evidence of abrupt changes in flora and fauna. There is some evidence that a substantial but short-lived climatic change may have happened in the early decades of the Paleocene. There are several theories about the cause of the K–Pg extinction event, with most evidence supporting the impact of a 10 km diameter asteroid forming the buried Chicxulub crater on the coast of Yucatan, Mexico; the end of the Paleocene was marked by a time of major change, one of the most significant periods of global change during the Cenozoic. The Paleocene–Eocene Thermal Maximum upset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminifera and a major turnover in mammals on land; the Paleocene is divided into three stages, the Danian, the Selandian and the Thanetian, as shown in the table above. Additionally, the Paleocene is divided into six Mammal Paleogene zones; the early Paleocene was cooler and drier than the preceding Cretaceous, though temperatures rose during the Paleocene–Eocene Thermal Maximum.
The climate became warm and humid worldwide towards the Eocene boundary, with subtropical vegetation growing in Greenland and Patagonia, crocodilians swimming off the coast of Greenland, early primates evolving in the tropical palm forests of northern Wyoming. The Earth's poles were temperate. In many ways, the Paleocene continued processes. During the Paleocene, the continents continued to drift toward their present positions. Supercontinent Laurasia had not yet separated into three continents - Europe and Greenland were still connected, North America and Asia were still intermittently joined by a land bridge, while Greenland and North America were beginning to separate; the Laramide orogeny of the late Cretaceous continued to uplift the Rocky Mountains in the American west, which ended in the succeeding epoch. South and North America remained separated by equatorial seas. Africa was heading north towards Europe closing the Tethys Ocean, India began its migration to Asia that would lead to a tectonic collision and the formation of the Himalayas.
The inland seas in North America and Europe had receded by the beginning of the Paleocene, making way for new land-based flora and fauna. Warm seas circulated including the poles; the earliest Paleocene featured a low diversity and abundance of marine life, but this trend reversed in the epoch. Tropical conditions gave rise including coral reefs. With the demise of marine reptiles at the end of the Cretaceous, sharks became the top predators. At the end of the Cretaceous, the ammonites and many species of foraminifera became extinct. Marine fauna came to resemble modern fauna, with only the marine mammals and the Carcharhinid sharks missing. Terrestrial Paleocene strata overlying the K–Pg boundary is in places marked by a "fern spike": a bed rich in fern fossils. Ferns are the first species to colonize areas damaged by forest fires. In general, the Paleocene is marked by the development of modern plant species. Cacti and palm trees appeared. Paleocene and plant fossils are attributed to modern genera or to related taxa.
The warm temperatures worldwide gave rise to thick tropical, sub-tropical and deciduous forest cover around the globe with ice-free polar regions covered with coniferous and deciduous trees. With no large browsing dinosaurs to thin them, Paleocene forests were denser than those of the Cretaceous. Flowering plants, first seen in the Cretaceous, continued to develop and proliferate, along with them coevolved the insects that fed on these plants and pollinated them. Mammals had first appeared in the Late Triassic, evolving from advanced cynodonts, developed alongside the dinosaurs, exploiting ecological niches untouched by the larger and more famous Mesozoic animals: in the insect-rich fo
Haemulinae is a subfamily of the Haemulidae and consists of the genera of that family which are regarded as being of New World origin, although they are now widespread. The following genera are included in the Haemulinae: Anisotremus Boridia Brachydeuterus Conodon Emmelichthyops Haemulon Haemulopsis Isacia Microlepidotus Orthopristis Parakuhlia Pomadasys Xenichthys Xenistius Xenocys