The Paleocene 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 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 brackets 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. It ended with the Paleocene–Eocene Thermal
Maximum. This was a geologically brief interval characterized by extreme
changes in climate and carbon cycling. The name "Paleocene" comes from Greek
and refers to the "old(er)" "new" fauna that arose during the epoch.
Boundaries and subdivisions 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, 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 Yucatan, Mexico.
The end of the Paleocene 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 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.
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 worldwide
towards the Eocene boundary, with subtropical vegetation growing in
Greenland and 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 temperate; North America, Europe, 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. 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. 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; 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 and
Europe had receded by the beginning of the Paleocene, making way for new
land-based flora and fauna. = 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. 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.
Flora Terrestrial 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 post-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 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 grazing dinosaurs to thin them, Paleocene forests were probably denser
than those of the Cretaceous. Flowering plants, 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 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 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 early mammal bones
are not well preserved in the fossil record, and most of what we know comes
from fossil teeth, and only a few skeletons.
The brain to body mass ratios of these archaic mammals were quite low.
Mammals of the Paleocene include: Monotremes: The ornithorhynchid
Obdurodon sudamericanum, in the family that includes the platypus, is the only
monotreme known from 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 and the North American Peradectes are two Paleocene
examples. Multituberculates: the only major branch
of mammals to become extinct since the K–Pg 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, proboscideans, and hoofed ungulates, including the condylarths and
the carnivorous mesonychids. = 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 champsosaurs, crocodilia,
soft-shelled turtles, palaeophi snakes, varanid lizards, and Protochelydra
zangerli. 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. 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.
Examples of Paleocene crocodylians are Borealosuchus formidabilis, the apex
predator and the largest animal of the Wannagan Creek fauna, and the
alligatorid Wannaganosuchus. 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 Paleocene
strata in New Mexico; but such stray late forms may be derived fossils.
= Birds= 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 Paleocene deposits, including
the omnivorous Gastornis in Europe and carnivorous terror birds in South
America, the latter of which survived until the Pleistocene.
In the late Paleocene, early owl types appeared, such as Ogygoptynx in the
United States and Berruornis in France. References
Ogg, Jim. "Overview of Global Boundary Stratotype Sections and Points".
Stratigraphy.org. Retrieved December 22, 2008.
External links Paleocene Mammals
BBC Changing Worlds: Paleocene Maryland Paleocene Fossils
Paleos: Paleocene Paleocene Evolutionary Radiation
PaleoMap Project John Alroy, "Evidence of a Paleocene
Evolutionary Radiation" Paleocene Microfossils: 35+ images of
Foraminifera Petrified Wood Museum Palaeocene
introduction Smithsonian Paleocene Introduction