Posts Tagged ‘American Miocene mammal diversity equals that of Africa’

The Faunal Diversity of Pleistocene North America was less than that of Modern Day Africa

December 9, 2013

Pleistocene North America has often been described as having a bestiary resembling that of the African continent.  I’ve probably even used this description myself.  This is not accurate.  The North American continent was home to a healthy ecosystem consisting of megafaunal herbivores, carnivores, and scavengers.  It was a vast unpeopled wilderness until man arrived and brought destruction upon many of the largest and most impressive species.  Yet, in species diversity, the North American Pleistocene doesn’t even come close to rivaling that of Africa.  There are 1100 species of mammals native to Africa compared to the 540 species of native North American mammals that lived during the Pleistocene–nearly double the number of species.  Yes, North America hosted 4 kinds of elephants, the unique giant ground sloths and armadillos, bison, camels, horse, peccaries, bears, big cats, and wolves. But Africa has 2 kinds of elephants, 2 kinds of rhinos, hippos, giraffes, hogs, zebras, and dozens of bovid species also known as antelopes.  Aardvarks and pangolins are every bit as unique as the edentates.  There are 60 species of carnivores, and 64 species of primates, including 5 species of apes. Until man arrived, North America’s Pleistocene had zero primates.

Giraffes.  We are fortunate that such a prehistoric-looking mammal still survives.  Toxodons, more massive but also with long necks, did live as far north as Mexico during the Pleistocene.  North America also hosted a long-necked species of camel during the Miocene.  The North American Miocene was more comparable to modern Africa in mammal species diversity than the Pleistocene.

Pangolin–every bit as primitive and unique as armadillos and ground sloths.

Mixed herd of elephants and wildebeest.  Wildebeest are one of many species of bovids.  Africa far outnumbers North America in species of bovids.  Antelope diversity here is amazing.

Baboon.  Africa outnumbered North American Pleistocene species of primates 60-1.

Africa is home to more species of mammals than any other continent.  Most of the African continent has never been subject to the seasonal subfreezing climates that have occurred in North America and Eurasia since early during the Pliocene.  Fewer species of mammals evolved the ability to survive in subfreezing climates, and I think this explains why Africa has a greater diversity of mammal species than any other continent.  This may not have always been the case.  During the Miocene (25 million BP-5 million BP), subfreezing climates did not occur over most of North America.  North America hosted at least 68 genera of hooved mammals during the Miocene compared with just 26 genera of hooved mammls during the Pleistocene.  It’s possible North American mammal diversity was equal to or higher  than in Africa during the Miocene.  So one could accurately describe the bestiary of Miocene North America as being similar to that of Africa.

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Not many end Pleistocene extinctions occurred on the African continent.  I think there are 2 reasons: a) tropical diseases formerly kept human populations lower in Africa than in other continents, and b) the animals living in Africa co-evolved with humans and were better adapted to avoid human hunters.  Of the handful of large Pleistocene mammals that did become extinct in Africa, scientists dispute whether some of them are actually different from living modern species.   The Cape horse (formerly Equus capensis) is now thought to be the same species as the living Grevy’s zebra.  The long-horned African buffalo (Pelobovirus antiquus) may have been a distinct species or just a large morph of the modern day water buffalo–its status is in dispute.  There was a large species of hartebeest (Megalotrigus priscus) that may have been overhunted into extinction.  The blue antelope (Hippotragus leuphagus) became extinct in 1800, possibly due to competition with domestic cattle.

The Sahara alternates cyclically between desert and well-watered savannah, depending on variations in earth’s tilt which change where oceanic monsoons bring precipitation to the African continent.  The Sahara has been in a desert cycle since 5000 BP.  During moist climatic cycles, some Eurasian species of mammals such as the extinct Eurasian rhino (Dicerorhinus kuchenbergensis), and the extinct Irish elk (Megalocerus) lived alongside giraffes, hippos, lions, and crocodiles in North Africa.  These species became extinct in Eurasia during a Sahara dry spell and couldn’t recolonize North Africa 12,000 years ago during the most recent moist phase of climate.

The giant deer or Irish elk–a widespread species in Eurasia.  The last known population of Irish elk lived in the Ural Mountains of Russia ~7700 BP.  This species periodically colonized North Africa when the Sahara desert became savannah following changes in the latitude of the monsoons.

Archaic species of hominids may have caused the early Pleistocene extinctions of several mid-sized carnivores that occupied the same omnivorous scavenging niche that early man did. A giant bear otter (Enhydridion dikikea) and a civet cat are among those mammals that Homo habilis may have extirpated.  Homo erectus may have wiped out a species of giant baboon (Therepithecus oswaldi), and there is archaeological evidence of a mass kill site.  It appears that a band of club-wielding Homo erectus slaughtered a whole troop of giant baboons.  Interestingly, the skull fractures indicate 93% of the blows were struck from right-handed men–the exact percentage of right-handers in the present day population. I also think humans are responsible for the extinction of Africa’s saber-tooth (Megentereon).  I hypothesize saber-tooths were a stubborn species that refused to give way when defending a carcass, unlike lions and hyenas that do retreat before a band of noisy stick-wielding hominids.

Fossil skull of extinct bear otter.  Lars Werdelin, a Swedish scientist, thinks Hominids outcompeted the giant bear otter and other mid-sized African carnivores into extinction during the late Pliocene and early Pleistocene.