New Year Special: Year of the Pig

Happy New Year! In China, it’s the Year of the Pig. Pigs have long been a mainstay of Eurasian societies since they were domesticated, proving critical protein for relatively low cost, and allowed for the Polynesians to conquer the Pacific and the Europeans to thrive in the New World.   The Egyptians considered them evil and diseased, and the Jewish and Muslim examples followed their example.   But it says something the Romans loved them so much they refused to adopt that dietary law. 

Pigs have been a success story in history.  It’s time to talk about their evolutionary story.

Pigs are basal artiodactyls-their closest relatives are the similarly Suine Peccaries, more basal camels, and more derived ungulates such as hippos, whales and extinct entelodonts, followed by camels, then by ruminants. 

 

So where do Suines come from? 

Appropriately enough, they seem to originate from East Asia. In the Eocene, we see piglike animals emerge. They’re distinct from anthracotheres and early whales-they’re not as anatomically specialized. Anthracotheres are cousins of hippos and entelodonts who resembled piglike hippos.  We find Egatochoerus and Siamochoerus in Thailand and Guangxi, alongside primitive Asian rodents, sabertooth nimravids (catlike predators that will get their own article), early ruminants, prosimian and early simian primates, and anthracotheres. 

In the Oligocene, we see them spread west-they reach Africa and Europe by 30 Million years ago. Palaeochoerus, for example, was found as far as Shantung, Zaragoza, and Angola. 

The Miocene sees an explosion of pigs as subfamily after subfamily emerges.

One is the long-legged Cainochoerus. They survived in Africa despite competition with antelope and warthogs until the mass extinction in the Pliocene.

There are the primitive, comospolitan Hyotheres. We see them in France, India, Russia and Spain, and have the beginnings of the characteristic tusks, long incisors, and unspecialized molars of living pigs.

Listriodon is far more similar to modern pigs, with a long snout and large tusks. They have a similar cosmopolitan range, and again died out in the Pliocene. Listriodon itself contains anything from 8 to 18 species as it seems to have existed for an incredible 10 million years, browsing across the continents.

Similar is the African Namachoerus, a short-snouted pig that resembles the hyotheres but is still closer to Listriodon. 

The most spectacular of these Miocene pigs is Kubanochoerus, a 1,000 lb pig from China, Russia and Kenya that infamously has a long, blunt horn in its forehead. The unicorn pig is found in the Middle Miocene during this pig flourishing, This horn is found in both sexes, which raises interesting questions about its function. It seems to have died out in the dryer, grassier climate of late Miocene.

Other giant pigs belonged to the plains dwelling browers, Tetraconodonts. They first appear in the mid-Miocene and go extinct at the end of the Miocene. Tetraconodon has nut (and possibly bone)-cracking teeth, living in open forests and parkland of Northern India, Pakistan and Myanmar. Sivachoereus appearing in both Kenya and Myanmar suggest this group originated in Africa and spread to Asia. 

A purely African genus, Nyanzachoerus, reached over 500 lbs and had a skull even lumbier and wartier than warthogs today. It evolved into Notochoerus, which reached up to 1,000 lbs and survived until the end of the Pliocene. Our ancestors must have seen these giant pigs, and given them a wide berth.  Western Tetracondonts included the smaller but still successful Conohyus and Retroporcus, which reached Europe and India early but went extinct quickly compared to the African tetraconodonts.

The True Pig subfamily contains many species living today, and many more that went extinct.  The earliest of the true pigs are the extinct late Miocene Hippohyids from China and India, but the other groups appear in the Pliocene and still exist today.

Warthogs are an African group that first appears in the Pliocene, and include the 700 lb, four-tusked omnivorous Metridiochoerus, the primitive southern Potamochoeroides, and Ethiopia’s Stylochoerus.

One clade includes African Red River Hogs and Giant Forest Hogs, but they were more widespread in the past-up to 500 lbs from the late Miocene, Propotamochoerus ranged from the Mediterranean to Southeast Asia and north into China and Russia. The Forest Hogs of Africa had a sister species in the denser forests, Kolpochoerus-they went extinct as the Pleistocene eliminated the forests. The giant-tusked, 700 lb Celebochoerus lived in the islands of Southeast Asia but otherwise resembled the giant forest hog.

Finally, we get to wild pig Sus and the nearly-extinct Pygmy hog of India. Their tribe dates back 10 million years. There’s the Italian Korynochoerus with its giant zygomatic arches, the 600 lb, slender-snouted and small tusked Microstonyx ranging from China to Spain, and the Pleistocene Hippopotamodon, found in Britain, the Mediterranean, and Southeast Asia.

The genus Sus appears in the late Miocene, appearing in Greece, Georgia, Moldova, China, Russia, Pakistan, Italy, Ukraine, Turkey and Lebanon. In the Pleistocene, Sus began to diversify; there was a group of Chinese and Indochinese pig species, while the long legged, 600 lb marsh-loving Sus strozzi lived in the Mediterranean.  

Sus scrofa, the wild boar of Eurasia and North Africa, is the ancestor of the domestic pigs, being domesticated about 7,000 BC. It appears that there were many independent domestications-in Turkey, in India, in Germany, in China, in New Guinea, and in Cyprus.  As a wild species, the wild boar displaced the previous Eurasian wild pigs, evolving in Indonesia about 800,000 years ago then invading the mainland, overrunning and outcompeting the most of the other pigs until it conquered Eurasia.  Indeed, the other members of the genus are all indigenous to Indonesia and the Philippines.   

The Wild boar has seen many strange creatures sharing its habitat-the giant ape Gigantopithecus, Stegodont cousins of elephants, cave bears, the Etruscan rhino, sabertooth cats, enormous steppe mammoths, European jaguar, stag-moose, giant deer, giant beaver, aurochs (which were similarly domesticated to cattle), other species of humans, early wolves, giant straight-tusked elephants, giant hyena, dwarf elephants and dwarf hippos, narrow-nosed rhinos, European ass and extinct species of horses, Merck’s rhino, giant cheetah,giant tapir, and genera of prehistoric cattle

One last pig has no close fossil relatives: the bizarre Babirusa, made of 4 species in Indonesia. This curly tusked pig is the most basal of surviving suines, but has no direct connection to any fossil or other extant species. 

Pigs exploded onto the scene 15 million years ago and still are among the most successful large mammals of all time. They combine brains, brawn, and versatility. And they’re going to be around for a long time. So let’s celebrate their history, and their prehistory. 

Another good article on pig evolution: https://synapsida.blogspot.com/2018/11/the-pig-family-fossil-pigs.html

For more on mammal evolution, I recommend Mammoths, Sabertooths and Hominids, written by Jordi Agusti and illustrated by Mauricio Anton