The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65.5 ± 0.3 Ma to 55.8 ± 0.2 Ma (
million years ago). It is the first epoch of the PalaeogenePeriod in the modern Cenozoicera. As with most other older geologic periods, the 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 eventat the end of the Cretaceous, known as the K-T boundary( Cretaceous- Tertiary), which marks the demise of the dinosaurs. 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") – "new" (Polytonic|καινός, "kainos") fauna that arose during the epoch, before modern mammalian orders emerged in the Eocene.
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
iridiumlevels. There is also fossil evidence of abrupt changes in flora and 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 km diameter asteroidforming the buried Chicxulub Crateron the coast of Yucatan, Mexico.
The end of the Paleocene (55.5/54.8 Ma) was marked by one of the most significant periods of global change during the Cenozoic. The
Paleocene-Eocene Thermal Maximumupset oceanic and atmospheric circulation and led to the extinction of numerous deep-sea benthic foraminiferaand a major turnover in mammals on land.
The Paleocene is divided into three stages, from youngest to oldest:
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 Greenlandand Patagonia, crocodiles swimming off the coast of Greenland, and early primates evolving in tropical palm forests of northern Wyoming [ [http://scicom.ucsc.edu/SciNotes/0301/warm/ Science Notes 2003: ] ] . The Earth's poles were cool and temperate; North America, Europe, Australiaand southern South Americawere warm and temperate; equatorial areas had tropical climates; and north and south of the equatorial areas, climates were hot and arid. [ [http://www.scotese.com/paleocen.htm PaleoMap Project: Paleocene Climate] ]
In many ways, the Paleocene continued processes that had begun during the late Cretaceous Period. During the Paleocene, the
continents continued to drift toward their present positions. Supercontinent Laurasiahad not yet separated into three continents - Europeand Greenlandwere still connected, North Americaand Asiawere still intermittently joined by a land bridge, while Greenland and North America were beginning to separate. 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] The Laramide orogenyof the late Cretaceous continued to uplift the Rocky Mountainsin 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 Gondwanalandcontinued to split apart, with Africa, South America, Antarcticaand Australiapulling away from each other. Africa was heading north towards Europe, slowly closing the Tethys Ocean, and Indiabegan 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.
Terrestrial Paleocene strata immediately overlying the K-T boundary is in places marked by a "
fernspike": a bed especially rich in fern fossils. [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] Ferns are often the first species to colonize areas damaged by forest fires; thus the fern spike may indicate post- Chicxulub Craterdevastation. [Phillip Bigelow. "The K-T Boundary In The Hell Creek Formation" (Accessed 7/15/06) http://www.scn.org/~bh162/k-t_boundary.html] In general, the Paleocene is marked by the development of modern plant species. Cacti and palm trees appeared. Paleocene and later plant fossils are generally attributed to modern 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 forests) with ice-free polar regions covered with coniferous and deciduous trees. With no large grazing dinosaurs to thin them, Paleocene forests were probably denser than those of the Cretaceous. [Stephen Jay Gould, ed., "The Book of Life" (New York: W.W. Norton & Company, 1993), p. 182.]
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.
Mammalshad first appeared in the Triassic, evolving from advanced cynodonts, and developed alongside the dinosaurs, exploiting ecological nichesuntouched by the larger and more famous Mesozoicanimals: in the insect-rich forest underbrush and high up in the trees. These smaller mammals (as well as birds, reptiles, amphibians, and insects) 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 niches. 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.
Paleocene mammals did not yet have specialized teeth or limbs, and their
brain to body mass ratios were quite low; compared to later forms, they are considered primitive, or archaic. [http://www.palaeos.com/Cenozoic/Paleocene/Paleocene.htm Palaeos.com: "The Paleocene". Accessed 11/26/06.] It was not until the Eocene, 55 Ma, that true modern mammals developed.
Mammals of the Paleocene include:
Monotremes: three species of monotremes have survived to modern times: the Platypus, and two species of Echidnas. " Monotrematum sudamericanum" lived during the Paleocene.
Marsupials: modern kangaroos 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".
*Placentals: this grouping of mammals became the most diverse and the most successful. Members include
primates, plesiadapids, and hoofed ungulates, including the condylarths and the carnivorous mesonychids.
Because of the climatic conditions of the Paleocene,
reptileswere more widely distributed over the globe than at present. Among the sub-tropicalreptiles found in North America during this epoch are champsosaurs (aquatic reptiles that resemble modern gharials), crocodilia, soft-shelled turtles, palaeophi snakes, varanid lizards, and " Protochelydra zangerli" (similar to modern snapping turtles).
Examples of champsosaurs of the Paleocene include "
Champsosaurusgigas", the largest champsosaur ever discovered. This creature was unusual among Paleocene reptiles in that "C. gigas" became larger than its known Mesozoicancestors: "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 euschian
crocodylid" Borealosuchus" (formerly " Leidyosuchus") "formidabilis", the apex predatorand the largest animal of the Wannagan Creekfauna, 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
Birds began to re-diversify during the epoch, occupying new niches. Most modern bird types had appeared by mid-Cenozoic, including perching birds, cranes,
hawks, pelicans, herons, owls, ducks, pigeons, loons, and woodpeckers.
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 Statesand " Berruornis" in France.
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. Tropical conditions gave rise to abundant marine life, 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 ammonitesand many species of foraminiferabecame extinct.
Marine faunas also came to resemble modern faunas, with only the marine mammals and the
* Ogg, Jim; June, 2004, "Overview of Global Boundary Stratotype Sections and Points (GSSP's)" http://www.stratigraphy.org/gssp.htm Accessed April 30, 2006.
* [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"]
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