The PALEOCENE ( /ˈpæliəˌsiːn, ˈpæ-, -lioʊ-/ ) or PALAEOCENE,
the "old recent", is a geologic epoch that lasted from about 66 to 56
million years ago. It is the first epoch of the
Paleogene Period in
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.
Paleocene Epoch brackets two major events in Earth's history. It
started with the mass extinction event at the end of the
known as the Cretaceous–
Paleogene (K–Pg) 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
Eocene Thermal Maximum , a geologically brief (~0.2
million year) interval characterized by extreme changes in climate and
The name "Paleocene" comes from
Ancient Greek and refers to the
"old(er)" (παλαιός, palaios) "new" (καινός, kainos) fauna
that arose during the epoch.
* 1 Boundaries and subdivisions
* 2 Climate
* 3 Paleogeography
* 3.1 Oceans
* 5.3 Birds
* 6 References
* 7 External links
BOUNDARIES AND SUBDIVISIONS
The K–Pg boundary that marks the separation between
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 happened in the very 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
The end of the
Paleocene (~55.8 Ma) was also 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
Paleocene is divided into three stages , the
Danian , the
Selandian and the
Thanetian , as shown in the table above.
Paleocene is divided into six
Paleocene was cooler and drier than the preceding
Cretaceous, though temperatures rose sharply during the
Eocene Thermal Maximum . The climate became warm and humid
worldwide towards the
Eocene boundary, with subtropical vegetation
Patagonia , crocodilians swimming off the
coast of Greenland, and early primates evolving in the tropical palm
forests of northern
Wyoming . The Earth's poles were cool and
North America ,
Australia and southern South
America were warm and temperate; equatorial areas had tropical
climates; and north and south of the equatorial areas, climates were
hot and arid, not dissimilar to today's global desert belts around 30
degrees northern and southern latitude.
In many ways, the
Paleocene continued processes that had begun during
Cretaceous Period. During the Paleocene, the continents
continued to drift toward their present positions. Supercontinent
Laurasia had not yet separated into three continents -
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.
North America remained separated by equatorial seas (they
joined during the
Neogene ); the components of the former southern
Gondwanaland continued to split apart, with
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
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.
Warm seas circulated throughout the world, including the poles. The
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 ammonites and
many species of foraminifera became extinct.
Marine fauna also came to resemble modern fauna, with only the marine
mammals and the
Carcharhinid sharks missing.
Paleocene strata immediately overlying the K–Pg
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
Chicxulub crater 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
The warm temperatures worldwide 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 browsing dinosaurs
to thin them,
Paleocene forests were probably denser than those of the
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.
Life restoration of
Mammals had first appeared in the
Late Triassic , evolving from
advanced cynodonts , 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 non-avian 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
non-avian 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 non-avian 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.
The brain to body mass ratios of these archaic mammals were quite
Mammals of the
* Monotremes : The ornithorhynchid
Obdurodon sudamericanum , in the
family that includes the platypus , is the only monotreme known from
Marsupials : modern kangaroos are marsupials, characterized by
giving birth to embryonic young, who crawl into the mother's pouch and
suckle until they are developed. The Bolivian
Pucadelphys andinus and
the North American Peradectes are two
Multituberculates : the only major branch of mammals to become
extinct since the K–Pg boundary, this rodent-like grouping includes
* Placentals : this grouping of mammals became the most diverse and
the most successful. Members include primates , plesiadapids ,
proboscideans , and hoofed ungulates, including the condylarths and
the carnivorous mesonychids .
Section of an
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
champsosaurs (fully aquatic reptiles), crocodilia , 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
Paleocene non-squamate 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). Another genus,
Simoedosaurus , was similarly large; it
appears rather suddenly in the fossil record, as it's closest
relatives occurred in the Early
Reptiles as a whole
decreased in size after the K–Pg event. Champsosaurs declined
towards the end of the
Paleocene and became extinct during the Miocene
Simoedosaurus , a
Paleocene choristodere .
Paleocene crocodylians are
Leidyosuchus ) formidabilis, the apex predator and the largest animal
Wannagan Creek fauna, and the alligatorid
Non-avian 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
Mexico ; but such stray late forms may be derived fossils .
Birds began to re-diversify during the epoch, occupying new niches.
Genetic studies suggest that nearly all modern bird clades can trace
their origin to this epoch, with
Neornithes having undergone an
extremely fast, "star-like" radiation of species in the early
Palaeocene in response to the vacancy of niches left by the
KT event .
Large flightless birds have been found in late
including the omnivorous
Europe and carnivorous terror
birds in South America, the latter of which survived until the
In the late Paleocene, early owl types appeared, such as Ogygoptynx
United States and
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Chronostratigraphic Chart (PDF), International Commission on
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Setter, eds., English Pronouncing Dictionary, Cambridge: Cambridge
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* ^ "Paleocene".
Online Etymology Dictionary
Online Etymology Dictionary .
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* ^ "
Paleocene Climate". PaleoMap Project . Retrieved 2012-08-28.
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* ^ Vajda, Vivi. "Global Disruption of Vegetation at the
Cretaceous-Tertiary Boundary – A Comparison Between the Northern and
Southern Hemisphere Palynological Signals". Gsa.confex.com. Retrieved
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Formation". Scn.org. Retrieved 2006-07-15.
* ^ Stephen Jay Gould, ed., The Book of Life (New York: W.W. Norton
& Company, 1993), p. 182.
* ^ Kazlev, M. Alan (2002) "The Paleocene". Palaeos Cenozoic.
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* ^ Musser, A. M. (2003). "Review of the monotreme fossil record
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* ^ Fassett, JE, Lucas, SG, Zielinski, RA, and Budahn, JR (2001).
"Compelling new evidence for
Paleocene dinosaurs in the Ojo Alamo
Sandstone, San Juan Basin, New
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* ^ Sullivan, RM (2003). "No
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* ^ Linnéa Smeds, Hans Ellegren, The Dynamics of Incomplete
Lineage Sorting across the Ancient Adaptive Radiation of Neoavian
* Ogg, Jim (June 2004). "Overview of Global Boundary Stratotype
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