Everything about The Paleocene totally explained
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
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)" (παλαιός,
palaios) – "new" (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
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-T 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 (55.5/54.8 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 usually broken into the Early, Middle, and Late Paleocene sub-epochs, which correspond to these
faunal stages, from youngest to oldest:
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. 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.
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 hadn't 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 (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. 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 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.
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
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 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's 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. It wasn't until the
Eocene, 55 Ma, that true modern mammals developed.
Mammals of the Paleocene include:
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 (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
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 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 fossils.
Birds
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 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.
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 faunas also came to resemble modern faunas, with only the marine mammals and the
Carcharhinid sharks missing.
Further Information
Get more info on 'Paleocene'.
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