For a little over twenty million years between the mid Eocene to early Miocene periods the entelodonts roamed across North America and Eurasia. Often considered to be ancient pigs, the exact relationship between enteledonts and modern pigs is an uncertain one that varies upon differing opinions.
What are entelodonts?
Although entelodonts are today usually interpreted as being pig-like (particularly warthogs), most palaeontologists are of the opinion that they are more closely related to mammals like hippos. This instead explains the similarity of entelodonts to pigs as a case of convergent evolution, a phenomena where two groups of animals evolve similar characteristics to cope with similar survival requirements. This might sound odd, but it is an idea not without precedent, in fact another group of mammals active at the same time as entelodonts were the nimravids which were very much like cats even though they evolved long before the first known members of the Felidae (true cats).
Other mammals of the time have also been considered to be related to the enteledonts, with the best known and perhaps most controversial case being Andrewsarchus. Often dubbed the biggest mammalian predator on land of all time, this mammal is so far only known from the skull, and most popular reconstructions are based upon another mammal called Mesonyx being used as a stand in for the missing body. Today however the overwhelming majority of palaeontologists agree that Mesonyx is not a reliable stand in, and so the body of Andrewsarchus remains unknown in form. However the skull of Andrewsarchus does bear a striking similarity to the skulls of entelodonts with a long snout, wide jugals and similar tooth arrangement and fossil remains are known from the same time period and approximate location of other entelodont remains. This had led to some cautious speculation that Andrewsarchus may be a closely related to entelodonts if not a different form of one, but without more complete confirmed Andrewsarchus remains being recovered it is impossible to prove this with certainty.
Entelodonts look weird. When you see a skeleton of an entelodont you can immediately pick up on the solid robust skull and the box like body, but the legs are so thin they seem unable to support a heavily built creature. The skull is carried forward from the body to the point where if you measure from the tip of the snout to the pelvis, the forelegs would actually be close to the midpoint of the measurement. The neck vertebrae do not look strong enough to carry such a large and heavy skull so far from the body, but it should be remembered that this was just part of the hard frame of the creature. In life these vertebrae would have been supported both above and below by incredibly powerful muscles, evidence for which comes from the enlarged neural spines of the forward dorsal vertebrae above the shoulders, and a robust sternum below reinforced by tightly packed ribs. These neck muscles would have been so well developed that they would have easily allowed entelodonts to move their heads around.
skull is noteworthy for being long with most of the width coming from
two greatly enlarged jugals (cheek bones). Popular thinking is
that these jugals would have allowed for the placement and attachment
of incredibly powerful jaw closing muscles. An additional theory
however is that the jugals would have made it difficult for a rival
entelodont to close its jaws around the head of another entelodont.
Both ideas are plausible, and it’s conceivable that both may apply
to entelodonts in general.
Entelodonts are also noted for having all four kinds of mammalian teeth, these being incisors at the front, followed by canines, then pre-molars until finally a rear battery of molars. The canines are the most striking teeth due to their proportionately large size to the other teeth to the point that they are virtually tusks. The incisors while small are actually a little more interesting since they point forwards instead of touching one another to form a shearing edge, but more on this in the next segment. As with all mammals the molar teeth are at the back of the mouth to take full advantage of the jaw closing muscles. By being towards the rear of the mouth the molars would be nearer the point of jaw articulation which meant that forces from the jaw closing muscles would be more focused upon whatever the entelodont was trying to grind or crush in its mouth.
Although an actual entelodont brain has never been preserved it is still possible to reconstruct the external physical dimensions by studying the cavity in the skull where the brain would have been. Studies have revealed two important things, one being that the brain was quite small when held in proportion to the rest of the body, two, the brain itself was quite primitive in its layout. Entelodont brains also seem to have been wired for making sense of external stimulae since for example the olfactory region (smell) seems to have been quite well developed in comparison to other areas. Altogether this has led to the idea that entelodonts were not problem solvers and instead lived by instinct rather than reason.
Entelodonts are classed within the Artiodactyla, a group better known either as ‘even-toed ungulates’ or more simply as the ‘hoofed mammals’. The actual hoofed feet of entelodonts were just two toes touching the ground while another two were raised off the ground. These toes not touching the ground are what are termed vestigial which means still present but no longer serving a practical purpose. The legs themselves are quite short when compared to the size of the body and is also the most gracile part. It’s realistic that over short distances entelodonts would have been competent runners capable of high speed; however they were simply not built for long distance running.
What did entelodonts eat?
This is probably the one question that has sparked the most interest about entelodonts. Due to the pig-like description so commonly applied to entelodonts, they have often been depicted as herbivores, probably using their large canines to root up buried plant parts such as tubers. More modern study of entelodonts however has yielded startling revelations about the true diets of entelodonts, namely that they absolutely were not strict herbivores.
Looking at the teeth again and the first clue that entelodonts were not dedicated herbivores comes from the types of teeth, in that they were all there, incisors, canines, premolars and molars. Strictly herbivorous mammals usually have a predominance of just incisors at the front and molars at the back, usually with a gap in-between where the canines and premolars would normally be called the diastema. Additionally the incisors that entelodonts have do not form a single shearing edge for cropping off plants and instead angle slightly forwards rather than just down. This would actually allow the incisors to easily project past the canines and physically grip a chunk of meat or a bone on a carcass so that it could be pulled free. Another factor to consider is the sheer bite force offered by the wide jugals and their connecting muscles, which would simply be beyond that necessary for a herbivorous animal.
The ‘smoking gun’ evidence that suggests entelodonts were meat eaters comes from numerous remains of Eocene to early Miocene era mammals from primitive rhinos and camels to even a chalicothere femur that still bear tooth marks in their preserved bones. When these tooth marks are matched up to the dental arrangements of other known mammals of the time, entelodonts often end up being the closest match and hence most likely animal to have caused them. There is even a collection of primitive camel remains that suggests that some entelodonts (in this case Archaeotherium) displayed caching behaviour which basically means they would horde animal parts for later consumption.
The one area that still cannot be ascertained with certainty regarding the diet of entelodonts is the proportions. The dentition of entelodonts was still capable of dealing with either a diet of meat or plants, and it’s not impossible that both types of food were eaten making entelodonts omnivores. One scenario could be that of entelodonts rooting through the ground for suitable plants, while also occasionally scavenging carcasses and bones to supplement their diet, perhaps to make up for a nutritional deficiency from the lack of a certain nutrients presence in the plants they were eating. It could also be however that entelodonts never ate plants at all but were hyper carnivores (eating absolutely nothing but meat). Alternatively the exact ratio between plants and meat may have depended upon the entelodont genus in question with some leaning more towards meat. All that can be said for certain is that at least some entelodonts did eat meat, but that now leads to ideas of how they acquired it.
Are entelodonts predators or
Although many people have described entelodonts as being ugly looking animals, one thing that cannot be denied is that they were built for power. Their box-like bodies and robust heavy skulls would have been surrounded by solid muscle, and for their size they were probably one of the heaviest types of mammal on the landscape. Most importantly this made the largest entelodonts a match for nearly every other type of herbivore and predator they were likely to come into contact with.
One idea is that entelodonts were actually dedicated predators of other animals. Here they could have lurked around denser growths of vegetation and/or watering holes where they could ambush unwary herbivores. They could then either use their bulk to knock their target off their feet or close their massive jaws around a critical area like the neck. Additionally the eye sockets in entelodont skulls are angled to face slightly forwards which means that entelodonts probably possessed a strong degree of depth perception that allowed them to gauge distances of objects, or perhaps in this context prey, that were in front of them. Although not entirely unknown in herbivores, such vision is more typical to predatory animals.
However not all palaeontologists are convinced about this kind of predator scenario and instead suggest that entelodonts were more likely scavengers. One particular point is that as hoofed animals, entelodonts were not capable of grabbing hold of prey. This would be a solid argument if not for the fact that not all predators try to hold their prey. Additionally once a prey animal was dead say for a bite from the jaws there would be no need to hold onto it and assuming that an animal was capable of delivering such a devastating bite, say a crocodile or one of the South American terror birds or even an entelodont, it is plausible.
Many fossils that bear entelodont-like tooth marks on them are skulls but these could be interpreted as supporting either hunting or scavenging. Most predators will try to hit a vulnerable area such as the neck and occasionally the head to try and kill their prey quickly. The head however does not have as much soft tissue on it as the rest of the body, and since a predator probably cannot eat a similarly sized animal in one go it will eat the softer areas such as the flanks and thighs first. The areas with less meat on such as the head and extremities like the feet do not normally get eaten until the more meaty areas have been finished, since the closer proximity of hard bone in these body parts increases the chance of tooth damage. It’s the less meaty areas that scavengers usually evolve to deal with since they are the areas most likely to be left. This is where the extreme bite force of entelodonts would be a significant advantage since they could crack the carcass bones and get at the bone marrow within, abilities that may have been beyond the original predator that brought it down.
More insight into how entelodonts acquired their meat comes from trackways that have been located in Toadstool Geologic Park, Nebraska, USA. Here there are many trackways of different mammals including herbivores like primitive rhinoceroses and carnivores such as Hyaenodon. What is even more interesting however are the trackways of entelodonts (probably of the genus Archaeotherium) that not only seem to follow some of these other tracks but do so in a zigzag pattern rather than a straight line. A zigzag pattern is no choice for chasing down an animal but it does allow an animals to track and zero in on another by scent.
What we do know about entelodonts is that they had reasonably good senses of smell, and by turning towards one direction and then another it could then sample the air for the strength of the scent. When the scent was stronger in one direction over the other, the entelodont would know to turn in that direction, steadily narrowing down the options until it was able to get a visual fix upon the source. Once found the entelodont could begin feeding upon the carcass, and if another carnivore was already there, possibly drive it away so that it could have the carcass to itself. Although not as exciting as the depiction of entelodonts as predators, if an entelodont could drive off other predators by intimidation alone it could live and eat with a reduced amount of energy expenditure as well as experience a significantly reduced risk of injury.
geographical distribution of entelodonts
Currently known entelodonts first appear around the Lutetian period of the Eocene with genera such as Brachyhyops. This genus is known from North America, though another genus from China called Eoentelodon has been speculated to be a synonym to Brachyhyops. This blurs the point of origin theory for entelodonts to possibly be Asia, though it’s perfectly possible that entelodonts could cross between Asia and North America over a land bridge that existed between these two continents at this time called Beringia. As such the precise point of origin for entelodonts remains uncertain, though future discoveries may help to clarify the issue.
During the late Eocene and Oligocene eras entelodonts seem to have been at their most numerous in terms of different genera. In addition they are known to have ranged across Eurasia and North America. However by the early Miocene entelodonts were on the decline and currently the latest known remains are dated to around the Burdigalian stage of the Miocene. This disappearance seems to have been global all at once with Burdigalian era remains being attributed to Asian and North American genera.
The popular conception of entelodonts regarding their size is that the earlier genera were small while the later genera grew larger, a pattern that is repeated in most animal groups. To an extent this is true for entelodonts since two of their largest genera (Paraentelodon and Daeodon) are known from Late Oligocene to early Miocene deposits. However to contradict this claim the type genus of the Entelodotnidae Entelodon is of a large size almost as big as these two later genera, yet Entelodon is dated farther back to the late Eocene to early Oligocene. This clearly indicates that even at this earlier stage in the entelodont timeline, there was still a niche for an exceptionally large genus.
This in turn could indicate that entelodonts evolved from more moderately to larger sized ancestors, they could quickly alter in terms of size of successive generations to even the possibility that we have yet to find the earliest entelodont ancestors. If the latter is true then future discoveries of entelodonts might be yielded from the earliest Eocene to possibly even the late Paleocene. Shifting to the other end of the scale and it’s not completely out of the question that entelodont fossils may one day be discovered later into the Miocene.
Extinction - Demise
of the Entelodonts
When looking for the exact cause as to why an animal that lived millions of years ago disappeared you have to consider all possibilities rather than get distracted by just looking for one single reason. In the case of entelodonts their disappearance seems to be tied in with on-going climate change of the Oligocene and Miocene epochs, but here it is other changes that occurred as a result of this climate change that more directly affected the entelodonts.
The main sequence of the climate change of this time is that of global cooling with the ecosystems on land changing from more tropical forests to open grasslands. If the entelodonts did eat plants or select parts of them such as tubers, then these changes in ecosystems could have triggered a decline and possibly a large scale disappearance in suitable plant types. Other groups of herbivores during the Oligocene to Miocene such as primitive horses were able to make the shift from browsing vegetation (that was slowly decreasing in density) to grazing grass (that was becoming more common) as can be seen from their changes in such features as teeth. Entelodonts as a group however display no such change which indicates that they either could not shift to eating new plant types, or alternatively didn’t eat plants.
This leads back to entelodonts being meat hunters, but let’s look at the idea of predation first. In the Eocene and Early Oligocene the vast majority of herbivores were browsers, and particularly in the Eocene there would still have been a lot of growth. This afforded both cover as well as making it unnecessary for herbivores to travel vast distance. This is why most herbivores had shorter legs that were less well adapted to running than their future descendants; the need for speed just wasn’t there. Entelodonts probably could run at high speeds over short distances, and could also use the cover of the extensive vegetation to approach herbivores. Even if a herbivore managed to spot an entelodont, the resulting chase would have probably been quite even.
The on-going shift towards more grassy areas however meant that the more successful herbivores were developing longer legs that were better able to carry them over distances, something that also allowed them to run faster. Additionally the increase in open grassy areas meant that there would have been less cover for entelodonts to approach meaning that they if they did hunt then they would have to run for longer after animals that were much better adapted to running than they were. Eventually this would mean expending more energy than they were getting from food resulting in starvation.
The third scenario which many consider to be the most likely is that entelodonts were scavengers that searched for carcasses while relying upon their bulk to drive off other predators that they might come across. Additionally entelodonts might have followed other predators and waited for them to make a kill just to drive them off afterwards. Scavenging like this might have always been a factor in entelodont behaviour, however the entelodonts, particularly later ones, may have been driven towards it due to their inability to hunt new types of faster herbivores or forage certain plants. During the Eocene and Oligocene entelodonts may have occasionally been going up against creodonts, nimravids, mesonychids, and early amphicyonids amongst others, all powerful predators, but most of these genera would have come up second when against the larger entelodont genera such as type genus Entelodon.
Other big genera such as Daeodon thrived into the early Miocene but now they were living in times that saw newer predators that were larger, meaner and perhaps most important of all, more intelligent than their predecessors that they had already largely replaced. Many of these predators such as the large bear dogs and another group of false sabre-toothed cats called the barbourofelids were more capable hunters that would have been able to offer much more of a fight even to the larger entelodont genera.
By the mid Miocene the remaining entelodonts were relics of an older and very different time. In this new era that they found themselves in they lacked a complete set of predator skills that would allow them to be deal with a variety of new herbivore types, and even with their immense physical power they could no longer bully the other meat eaters into giving up their food. The change in plant types may have also made it difficult for them to switch to a more herbivorous diet that would take them out of direct competition with the newer and more competent predators, many of which now likely had the jaw power to process all of a carcass leaving little to nothing for the entelodonts to clear up. Outclassed and not adapting to a new lifestyle meant that it would only be a matter of time before the entelodonts vanished.
Daeodon (Now also includes Dinohyus)
Entelodon (Now also includes Elotherium)