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Paleocene

2007 Schools Wikipedia Selection. Related subjects: Geology and geophysics

   The Paleocene, "early dawn of the recent", is a geologic epoch that
   lasted from 65 Mya to 56 Mya ( million years ago). It is the first
   epoch of the Palaeogene Period in the modern Cenozoic era. 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 event at
   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) (paleo) – new
   (ceno)" fauna that arose during the epoch, prior to the emergence of
   modern mammalian orders in the Eocene.

Paleocene 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 and fauna. There is
   some evidence that a substantial but very short-lived climatic change
   may have occurred in the very early decades of the Paleocene. There are
   a number of theories about the cause of the K-T extinction event, with
   most evidence supporting the impact of a 10 km diameter asteroid near
   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, a sudden
   global change, the Paleocene-Eocene Thermal Maximum, which upset
   oceanic and atmospheric circulation and led to the extinction of
   numerous deep-sea benthic foraminifera and on land, a major turnover in
   mammals.

   The Paleocene is usually broken into early, middle, and late sub-epochs
   which correspond to the following faunal 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)

Paleocene climate

   The early Paleocene was slightly cooler than the preceding Cretaceous,
   though temperatures rose again late in the epoch. The climate was warm
   and humid world-wide, with subtropical vegetation growing in Greenland
   and Patagonia. The poles were cool and temperate, North America,
   Europe, Australia and southern South America were warm and temperate;
   tropical climates characterized equatorial areas, and North and South
   of the Equator climates were hot and arid.

Paleocene paleogeography

   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. North America and
   Asia were still intermittently joined by a land bridge, while Greenland
   and North American were beginning to separate. The Laramide orogeny of
   the late Cretaceous continued to uplift the Rocky Mountains in the
   American west, only ending in the succeeding epoch.

   South and North America remained separated by equatorial seas, only
   joining 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 the
   huge tectonic collision and 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.

Paleocene 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. Ferns are often the first species to colonize areas damaged by
   forest fires; thus the fern spike may indicate post- Chicxulub
   devastation.

   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.

   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.

Paleocene fauna

Mammals

   Mammals had first appeared in the Triassic, 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 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 with herbivorous and
   insectivorous diets, the demise of the dinosaurs and the beginning of
   the Paleocene saw mammals growing bigger, more ferocious, and finally
   becoming the dominant predators and spreading throughout the world. 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.

   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. It was not until the
   Eocene, 55 Ma, that true modern mammals developed.

   Fossil evidence from the Paleocene is scarce, and there is relatively
   little known about mammals of the time. Because of their small size--a
   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.

   Mammals of the Paleocene include:
     * Monotremes: three species of monotremes have survived to modern
       times: the duck-billed 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 extinct mammalian family, this
       rodent-like grouping includes the Paleocene Ptilodus.
     * Placentals: this grouping of mammals became the most diverse and
       the most successful. Members include hoofed ungulates, primates and
       carnivores, such as the Paleocene mesonychid.

Reptiles

   Due to 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
   champsosaurs (aquatic reptiles that resemble modern gharials),
   crocodilians, soft-shelled turtles, palaeophid snakes, varanid lizards,
   and Protochelydra zangerli (similar to modern 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 euschian crocodylid
   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.

Birds

   Birds began to 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.

   Early owl types such as Ogygoptynx and Berruornis appear in the late
   Paleocene in the U.S. and France respectively.

Paleocene 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. 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. The end of the Cretaceous also saw extinctions of
   the ammonites, and many species of foraminifera.

   Marine faunas also came to resemble modern faunas, with only the marine
   mammals and the Charcharinid sharks missing.
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