Known as 'terminator pigs or ‘hell pigs’ entelodonts are just as terrifying as their nicknames suggest, says Will Newton.
What were terminator pigs aka entelodonts?
The entelodonts were a family of hoofed, pig-like mammals that ranged across the northern hemisphere from the Middle Eocene (around 40 million years ago) to the Early Miocene (around 16 million years ago). While they superficially resemble pigs and, like today’s pigs, were notorious for gobbling down anything edible they came across, entelodonts are actually more closely related to hippos and whales.
When did 'hell pigs' first appear?
It’s unclear exactly what group of mammals entelodonts evolved from, but the first of them - Proentelodon and Eoentelodon - appeared in China and Mongolia roughly 40 million years ago during the Eocene.
These early entelodonts were small compared to those that would go on to stalk the vast prairies of North America during the Oligocene and the Miocene, standing about as tall as today’s pigs (~80cm) and weighing in at around 150kg.
From East Asia, entelodonts spread west and east, evolving into many different forms as they adapted to new niches in Europe and North America. This migration of early entelodonts coincided with a significant increase in body size, in both Eurasian and North American forms. This is the point, ~35 million years ago, that entelodonts really started to grow into their nickname of ‘Hell Pigs’, or ‘Terminator Pigs’.
What was the largest 'hell pig'?
As entelodonts spread across the northern hemisphere and diversified, their skulls got larger and larger, to the point where they made up more than a quarter of the animals’ length in the case of Daeodon - the largest entelodont ever discovered and perhaps one of the most deadly animals to set foot in North America during the Cenozoic Era (~66 million years ago to the present).
How big was Daeodon?
Daeodon stood roughly 2m tall, weighed in at half-a-ton, and had a head that was almost a metre long, or 35% of its total body length. To support such a large head, Daeodon had a set of unusually long neural spines between its shoulders, which formed a muscular hump similar to today’s bison. This hump served as the attachment point for a series of giant muscles that ran through Daeodon’s neck and supported its head.
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Daeodon’s jaws were incredibly strong, capable of crushing bones, and lined with an array of large, specialised teeth. Like other entelodonts, Daeodon had long incisors, sturdy canines, and square-shaped molars - hallmarks of an animal that ate both meat and plants.
These teeth were also covered in a remarkably thick layer of enamel, which strengthened them and allowed Daeodon (and many other types of entelodonts) to crack bones and get at the calorie-rich marrow hidden inside, just like today’s hyenas do.
How smart was Daeodon?
While Daeodon’s skull was massive, its braincase was actually quite small, meaning it probably wasn’t the smartest animal of its time. That said, based on studies of the cavities inside its skull, researchers think it may have had large olfactory lobes. These are the parts of the brain that process smells, so it’s thought that Daeodon had a particularly keen nose and was capable of picking up the scents of prey animals, or dead carcasses, from miles away.
What did entelodonts eat?
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Entelodonts were omnivores and likely ate a range of different foods, from nuts, roots, and vines, to meat and bones. The extent to which they may have eaten meat is debated, but from patterns of wear on their teeth it’s clear that they sometimes treated themselves to a steak dinner.
While they looked like today’s pigs, entelodonts were typically taller, with slimmer, longer legs that were designed for running long distances. This, in addition to the rest of their anatomy, their large olfactory lobes, and stereoscopic vision, has led to the generally accepted conclusion that they were predators, as well as opportunistic scavengers.
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It’s unclear exactly how entelodonts hunted, though based on a set of fossilised footprints found in lockstep with those of a hornless rhino (Subhyracodon) in northwest Nebraska, it has been suggested that they were ambush predators. The remains of small camels, known as Poebrotherium, and chalicotheres, strange, plant-eating mammals that look like a cross between a gorilla and a giraffe, have also been found covered in bite marks that line up with the teeth of entelodonts.
There are signs of bite marks made by entelodonts on other entelodonts too. This isn’t necessarily a sign that they hunted one another, rather evidence that they regularly engaged in deadly duels, likely for territory, food, or mates. From a study of 170 entelodont skulls, it was found that at least 7% had signs of healed bite marks on their face or snout, almost certainly inflicted by another entelodont.
A similar study on entelodont skulls also revealed that they were capable of opening their jaws to an incredibly wide degree - as much as 109° in the case of Archaeotherium. This may have allowed entelodonts to ‘jaw wrestle’, just like some of their closest living relatives, hippos, do today. They also had strange, bony projections that jutted out of their jaws, known as mandibular tubercles. It’s thought these tubercles may have played a role in head-to-head combat, or that they were used for display and attracting potential mates.
Why did entelodonts become extinct?
The last entelodonts met their end roughly 16 million years ago during the Early Miocene. The reasons behind the extinction of the entelodonts are somewhat mysterious, as omnivorous, opportunistic animals like them are usually quite resilient to climate change.
It has been suggested that competition with another group of large, predatory mammals - known as amphicyonids, or bear dogs - may have contributed to their demise. The arrival of big cats (or Felidae) into entelodonts’ territories from 30 million years ago probably didn’t help them either, further increasing their trajectory towards extinction.
Another idea as to why entelodonts became extinct is that they may have been particularly sensitive to droughts. A large number of entelodonts have been found in North Central US (South Dakota and Nebraska) next to or near dried-up watering holes. We know from isotope records that droughts became a lot more common in the Miocene, particularly in North America where many species of entelodonts lived.
Still, despite ultimately facing extinction, entelodonts persisted for more than 20 million years and ranged across Europe, Asia, and North America, making them one of the most successful predators of the Cenozoic. The ‘Hell Pigs’ were, in many ways, the T.rex of the Cenozoic and more comparable to the big bad wolf in the classic children’s story, than the three little pigs.
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