Primeval 26 – Pliocene Epoch

 

The Pliocene Epoch is the period in the geologic timescale that extends from 5.333 million to 2.58 million years before present. Prior to the 2009 revision of the geologic time scale, which placed the 4 most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian stage, which lasted from 2.588 to 1.806 million years ago, and is now included in the Pleistocene.(1)James George Ogg et al. (2008) The Concise Geologic Time Scale, Pages 150–151

Chalicotherium in the Early Pliocene

Chalicotherium in the Early Pliocene

Continents continued to drift, moving from positions possibly as far as 250 km from their present locations to positions only 70 km from their current locations. South America became linked to North America through the Isthmus of Panama during the Pliocene, making possible the Great American Interchange and bringing a nearly complete end to South America’s distinctive large marsupial predator and native ungulate animals. The formation of the Isthmus had major consequences on global temperatures, since warm equatorial ocean currents were cut off and an Atlantic cooling cycle began, with cold Arctic and Antarctic waters dropping temperatures in the now-isolated Atlantic Ocean.

The change to a cooler, dry, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species worldwide. Deciduous forests proliferated, coniferous forests and tundra covered much of the north, and grasslands spread on all continents except Antarctica. Like today tropical forests were limited to a tight band around the equator, and dry savannahs and deserts dominated Asia and Africa.

Glyptodontidae, Extinct relatives of Armadillos

Glyptodontidae, Extinct relatives of Armadillos

In North America, rodents, large mastodons and gomphotheres, and opossums continued successfully, while hoofed animals declined, with camel, deer and horse all seeing populations recede. North American rhinoceroses, three toed horses, oreodonts, protoceratids, and chalicotheres went extinct. Ground sloths, huge glyptodonts, and armadillos migrated north from South America after the formation of the Isthmus of Panama. South America was invaded by North American species for the first time since the Cretaceous, with North American rodents and primates mixing with southern forms. Litopterns and the notoungulates, South American natives, were mostly wiped out, except for the macrauchenids and toxodonts, which managed to survive. Small weasel-like carnivorous mustelids, coatis and short faced bears migrated from the north. Grazing glyptodonts, browsing giant ground sloths and smaller caviomorph rodents, pampatheres, and armadillos did the opposite, migrating to the north and thriving there.

In Eurasia rodents did well, while primate distribution declined. Elephants, gomphotheres and stegodonts were successful in Asia, and hyraxes migrated north from Africa. Horse diversity declined, while tapirs and rhinoceroses did fairly well. Cattle and antelopes were successful, and some camel species crossed into Asia from North America. Hyenas and early saber-toothed cats appeared, joining other predators including dogs, bears and weasels. Africa was dominated by hoofed animals, and primates continued their evolution, with some of the first hominids, the australopithecines appearing in the late Pliocene. Rodents, elephants, cattle, and antelopes were all successful in Africa. Early giraffes appeared, and camels migrated to Africa via Asia from North America. Bears, dogs and weasels joined cats, hyenas and civets as the African predators, forcing hyenas to adapt as specialized scavengers. The marsupials remained the dominant Australian mammals, with herbivore forms including wombats and kangaroos, and the huge diprotodon. Carnivorous marsupials continued hunting in the Pliocene, including dasyurids, the dog-like thylacine and cat-like thylacoleo. The first rodents arrived in Australia and the modern platypus appeared.

Macrauchenia in the Pliocene

Macrauchenia in the Pliocene

The global average temperature in the mid-Pliocene around 3.3 to 3 million years ago was 2 to 3°C higher than today,(2)Marci M. Robinson (2008) “Pliocene role in assessing future climate impacts” Eos, Transactions American Geophysical Union, Volume 89, Pages 501–502 global sea level 25 m higher(3)Gary S. Dwyer and Mark A. Chandler (2009) “Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes.” Philosophical Transactions of the Royal Society A, Volume 367, Pages 157–168 and the Northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 million years ago.(4)G. Bartoli et al. (2005) “Final closure of Panama and the onset of northern hemisphere glaciation” Earth and Planetary Science Letters, Volume 237, Page 3344 The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds.(5)Tjeerd H. van Andel (1994) New Views on an Old Planet: a History of Global Change Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.

The mid Pliocene warm period is considered a potential analog of future climate. The intensity of the sunlight reaching the earth, the global geography, and carbon dioxide concentrations were similar to present. Many mid-Pliocene species are extant helping paleotemperature proxies calibration. Model simulations of mid-Pliocene climate produce warmer conditions at middle and high latitudes, as much as 10–20° Celsius warmer than today above 70° North. They also indicate little temperature variation in the tropics. Model-based biomes are generally consistent with Pliocene paleobotanical data indicating a northward shift of the Tundra and Taiga and an expansion of Savanna and warm-temperate forest in Africa and Australia.(6)U. Salzmann et al. (2009). “The past is a guide to the future? Comparing Middle Pliocene vegetation with predicted biome distributions for the twenty-first century” Philosophical Transactions of the Royal Society A, Volume 367, Number 1886 Pages 189–204

References   [ + ]

1. James George Ogg et al. (2008) The Concise Geologic Time Scale, Pages 150–151
2. Marci M. Robinson (2008) “Pliocene role in assessing future climate impacts” Eos, Transactions American Geophysical Union, Volume 89, Pages 501–502
3. Gary S. Dwyer and Mark A. Chandler (2009) “Mid-Pliocene sea level and continental ice volume based on coupled benthic Mg/Ca palaeotemperatures and oxygen isotopes.” Philosophical Transactions of the Royal Society A, Volume 367, Pages 157–168
4. G. Bartoli et al. (2005) “Final closure of Panama and the onset of northern hemisphere glaciation” Earth and Planetary Science Letters, Volume 237, Page 3344
5. Tjeerd H. van Andel (1994) New Views on an Old Planet: a History of Global Change
6. U. Salzmann et al. (2009). “The past is a guide to the future? Comparing Middle Pliocene vegetation with predicted biome distributions for the twenty-first century” Philosophical Transactions of the Royal Society A, Volume 367, Number 1886 Pages 189–204