Paleocene 23252 221076700 2008-06-22T23:21:53Z Firsfron 158443 clean up, Replaced: [[dinosaurs]] → [[dinosaur]]s using [[Project:AutoWikiBrowser|AWB]] {{TOCright}} The '''Paleocene''' or '''Palaeocene''', "early dawn of the recent", is a geologic [[epoch (geology)|epoch]] that lasted from 65.5 ± 0.3 [[Mega-annum|Ma]] to 55.8 ± 0.2 Ma ([[million years ago]]). It is the first epoch of the [[Palaeogene]] [[Period (geology)|Period]] in the modern [[Cenozoic]] [[era (geology)|era]]. As with most other older [[geologic timescale|geologic periods]], the [[Stratum|strata]] that define the epoch's beginning and end are well identified but the exact date of the end is uncertain. The Paleocene epoch immediately followed the mass [[extinction event]] at the end of the [[Cretaceous]], known as the [[K-T boundary]] ([[Cretaceous]] - [[Tertiary]]), which marks the demise of the [[dinosaur]]s. The die-off of the dinosaurs left unfilled ecological niches worldwide, and the name "Paleocene" comes from Greek and refers to the "old(er)" ({{Polytonic|παλαιός}}, ''palaios'') &ndash; "new" ({{Polytonic|καινός}}, ''kainos'') [[fauna (animals)|fauna]] that arose during the epoch, before modern [[mammal]]ian [[Linnaean taxonomy|orders]] emerged in the [[Eocene]]. {{Paleogene Footer}} ==Boundaries and subdivisions== The K-T 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, with high [[iridium]] levels. There is also fossil evidence of abrupt changes in [[flora (plants)|flora]] and [[fauna (animals)|fauna]]. There is some evidence that a substantial but very short-lived climatic change may have happened in the very early decades of the Paleocene. There are several theories about the cause of the K-T extinction event, with most evidence supporting the impact of a 10&nbsp;km [[diameter]] [[asteroid]] forming the buried [[Chicxulub Crater]] on the coast of [[Yucatan]], [[Mexico]]. The end of the Paleocene (55.5/54.8&nbsp;Ma) was marked by 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 [[stage (geology)|stages]], from youngest to oldest: {| | [[Thanetian]] | (58.7 ± 0.2 – 55.8 ± 0.2 Ma) |- | [[Selandian]] | (61.7 ± 0.2 – 58.7 ± 0.2 Ma) |- | [[Danian]] | (65.5 ± 0.3 – 61.7 ± 0.2 Ma) |} ==Climate== The early Paleocene was cooler and dryer than the preceding Cretaceous, though temperatures rose sharply during the [[Paleocene–Eocene Thermal Maximum]]. The climate became warm and humid world-wide towards the Eocene boundary, with subtropical vegetation growing in [[Greenland]] and [[Patagonia]], crocodiles swimming off the coast of Greenland, and early primates evolving in tropical palm forests of northern Wyoming<ref>[http://scicom.ucsc.edu/SciNotes/0301/warm/ Science Notes 2003:<!-- Bot generated title -->]</ref>. The Earth's poles were cool and temperate; [[North America]], [[Europe]], [[Australia]] and southern [[South America]] were warm and temperate; equatorial areas had tropical climates; and north and south of the [[equator]]ial areas, climates were hot and arid. <ref>[http://www.scotese.com/paleocen.htm PaleoMap Project: Paleocene Climate]</ref> ==Paleogeography== In many ways, the Paleocene continued processes that had begun during the late Cretaceous Period. During the Paleocene, the [[continent]]s 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. <ref name="Hooker"> Hooker, J.J., "Tertiary to Present: Paleocene", pp. 459-465, Vol. 5. of Selley, Richard C., L. Robin McCocks, and Ian R. Plimer, Encyclopedia of Geology, Oxford: Elsevier Limited, 2005. ISBN 0-12-636380-3</ref> 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 (they joined during the [[Neogene]]); the components of the former southern supercontinent [[Gondwanaland]] continued to split apart, with [[Africa]], South America, [[Antarctica]] and [[Australia]] pulling away from each other. Africa was heading north towards [[Europe]], slowly closing the [[Tethys Ocean]], and [[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 ([[Western Interior Seaway]]) and Europe had receded by the beginning of the Paleocene, making way for new land-based flora and fauna. ==Flora== Terrestrial Paleocene strata immediately overlying the K-T boundary is in places marked by a "[[fern]] spike": a bed especially rich in fern fossils.<ref>Vajda, Vivi. "Global Disruption of Vegetation at the Cretaceous-Tertiary Boundary – A Comparison Between the Northern and Southern Hemisphere Palynological Signals" (Accessed 7/15/06) http://gsa.confex.com/gsa/2004AM/finalprogram/abstract_81135.htm</ref> Ferns are often the first species to colonize areas damaged by [[forest fires]]; thus the fern spike may indicate post-[[Chicxulub Crater]] devastation.<ref>Phillip Bigelow. "The K-T Boundary In The Hell Creek Formation" (Accessed 7/15/06) http://www.scn.org/~bh162/k-t_boundary.html</ref> In general, the Paleocene is marked by the development of modern plant species. [[Cactus|Cacti]] and [[palm tree]]s appeared. Paleocene and later plant [[fossil]]s are generally attributed to modern [[Genus|genera]] or to closely related taxa. The warm temperatures world-wide gave rise to thick tropical, sub-tropical and deciduous forest cover around the globe (the first recognizably modern [[rain forest]]s) with ice-free polar regions covered with coniferous and deciduous trees. <ref name="Hooker"/> With no large grazing dinosaurs to thin them, Paleocene forests were probably denser than those of the Cretaceous.<ref>Stephen Jay Gould, ed., ''The Book of Life'' (New York: W.W. Norton & Company, 1993), p. 182.</ref> Flowering plants ([[angiosperms]]), first seen in the Cretaceous, continued to develop and proliferate, and along with them coevolved the insects that fed on these plants and pollinated them. ==Fauna== ===Mammals=== [[Mammals]] had first appeared in the [[Triassic]], evolving from advanced [[cynodont]]s, and developed alongside the dinosaurs, exploiting [[ecological niches]] untouched by the larger and more famous [[Mesozoic]] animals: in the insect-rich forest underbrush and high up in the trees. These smaller mammals (as well as [[bird]]s, [[reptile]]s, [[amphibian]]s, and [[insect]]s) survived the mass extinction at the end of the Cretaceous which wiped out the dinosaurs, and mammals diversified and spread throughout the world. While early mammals were small nocturnal animals that mostly ate soft plant material and small animals such as insects, the demise of the dinosaurs and the beginning of the Paleocene saw mammals growing bigger and occupying a wider variety of [[ecological niche]]s. Ten million years after the death of the dinosaurs, the world was filled with rodent-like mammals, medium sized mammals scavenging in forests, and large herbivorous and carnivorous mammals hunting other mammals, birds, and reptiles. Fossil evidence from the Paleocene is scarce, and there is relatively little known about mammals of the time. Because of their small size (constant until late in the epoch) early mammal bones are not well-preserved in the fossil record, and most of what we know comes from fossil teeth (a much tougher substance), and only a few skeletons.<ref name="Hooker"/> Paleocene mammals did not yet have specialized teeth or limbs, and their [[brain to body mass ratio]]s were quite low; compared to later forms, they are considered primitive, or archaic. <ref>http://www.palaeos.com/Cenozoic/Paleocene/Paleocene.htm Palaeos.com: "The Paleocene". Accessed 11/26/06.</ref> It was not until the [[Eocene]], 55&nbsp;Ma, that true modern mammals developed. Mammals of the Paleocene include: *[[Monotreme]]s: three species of monotremes have survived to modern times: the [[duck-billed platypus]], and two species of [[Echidna]]s. ''[[Monotrematum sudamericanum]]'' lived during the Paleocene. *[[Marsupials]]: modern [[kangaroo]]s are marsupials, characterized by giving birth to embryonic babies, who crawl into the mother's pouch and suckle until they are developed. The Bolivian ''[[Pucadelphys andinus]]'' is a Paleocene example. *[[Multituberculates]]: the only major branch of mammals to go extinct since the K-T boundary, this rodent-like grouping includes the Paleocene ''[[Ptilodus]]''. *[[Placentalia|Placentals]]: this grouping of mammals became the most diverse and the most successful. Members include [[primates]], [[plesiadapid]]s, and hoofed ungulates, including the [[condylarth]]s and the carnivorous [[mesonychid]]s. ===Reptiles=== Because of the climatic conditions of the Paleocene, [[reptiles]] were more widely distributed over the globe than at present. Among the [[sub-tropical]] reptiles found in North America during this epoch are [[champsosaur]]s (aquatic reptiles that resemble modern [[gharial]]s), [[crocodilia]], soft-shelled [[turtles]], palaeophi [[snakes]], [[Varanidae|varanid lizards]], and ''[[Protochelydra zangerli]] '' (similar to modern [[Chelydridae|snapping turtles]]). Examples of champsosaurs of the Paleocene include ''[[Champsosaurus]] gigas'', the largest champsosaur ever discovered. This creature was unusual among Paleocene reptiles in that ''C. gigas'' became larger than its known [[Mesozoic]] ancestors: ''C. gigas'' is more than twice the length of the largest Cretaceous specimens (3 meters versus 1.5 meters). Reptiles as a whole decreased in size after the K-T event. Champsosaurs declined towards the end of the Paleocene and became extinct at the end of the Eocene. Examples of Paleocene crocodylians are the [[Eusuchia|euschian]] [[crocodylid]] ''[[Borealosuchus]]'' (formerly ''[[Leidyosuchus]]'') ''formidabilis'', the [[apex predator]] and the largest animal of the [[Wannagan Creek]] fauna, and the [[alligatorid]] ''[[Wannaganosuchus]]''. Dinosaurs may have survived to some extent into the early Danian stage of the Paleocene Epoch circa 64.5 Mya. The controversial evidence for such is a hadrosaur leg bone found from Paleocene strata from 64.5 Mya in Australia; but such stray late forms may be [[derived fossil]]s. ===Birds=== [[Image:Gastornis.jpg|thumb|right|140px|Gastornis]] Birds began to re-diversify during the epoch, occupying new niches. Most modern bird types had appeared by mid-Cenozoic, including [[passerine|perching bird]]s, [[crane (bird)|crane]]s, [[hawk]]s, [[pelican]]s, [[heron]]s, [[owl]]s, [[duck]]s, [[dove|pigeon]]s, [[loon]]s, and [[woodpecker]]s. Large carnivorous flightless birds (also called [[Terror Birds]]) have been found in late Paleocene fossils, including the fearsome ''[[Gastornis]]'' in Europe. In the late Paleocene, early owl types appeared, such as ''[[Ogygoptynx]]'' in the [[United States]] and ''[[Berruornis]]'' in [[France]]. ==Oceans== Warm seas circulated throughout the world, including the poles. The earliest Paleocene featured a low diversity and abundance of marine life, but this trend reversed later in the epoch. <ref name="Hooker"/> Tropical conditions gave rise to abundant marine life, including [[coral reef]]s. With the demise of marine reptiles at the end of the Cretaceous, [[shark]]s became the top predators. At the end of the Cretaceous, the [[ammonites]] and many species of [[foraminifera]] became extinct. Marine faunas also came to resemble modern faunas, with only the marine mammals and the [[Carcharhinid]] sharks missing. ==References== <references/> * Ogg, Jim; June, 2004, ''Overview of Global Boundary Stratotype Sections and Points (GSSP's)'' http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006. ==External links== *[http://paleocene-mammals.de/ Paleocene Mammals] *[http://www.bbc.co.uk/beasts/changing/paleocene/index.shtml BBC Changing Worlds: Paleocene] *[http://www.itano.net/fossils/marylan2/marylan2.htm Maryland Paleocene Fossils] *[http://www.palaeos.com/Cenozoic/Paleocene/Paleocene.htm Paleos: Paleocene] *[http://www.nceas.ucsb.edu/~alroy/Paleocene.html Paleocene Evolutionary Radiation] *[http://scotese.com/ PaleoMap Project] *[http://www.nceas.ucsb.edu/~alroy/Paleocene.html John Alroy, "Evidence of a Paleocene Evolutionary Radiation"] {{Commonscat|Paleocene}} {{Cenozoic Footer}} [[Category:Paleocene| ]] [[ast:Paleocenu]] [[br:Paleosen]] [[ca:Paleocè]] [[cs:Paleocén]] [[da:Paleocæn]] [[de:Paläozän]] [[et:Paleotseen]] [[es:Paleoceno]] [[eo:Paleoceno]] [[fr:Paléocène]] [[ko:팔레오세]] [[id:Paleosen]] [[it:Paleocene]] [[he:פליאוקן]] [[lb:Paläozän]] [[hu:Paleocén]] [[nl:Paleoceen]] [[ja:暁新世]] [[no:Paleocen]] [[nn:Paleocen]] [[nds:Paläozän]] [[pl:Paleocen]] [[pt:Paleoceno]] [[ro:Paleocen]] [[sh:Paleocen]] [[fi:Paleoseenikausi]] [[sv:Paleocen]] [[vi:Thế Paleocen]] [[tr:Paleosen]] [[uk:Палеоцен]] [[zh:古新世]]