I am writing this with tears streaming down my face. Yesterday I had to say goodbye to my baby Luca, my childhood dog.
My poor baby was diagnosed with lymphoma over a month ago. He was a 12-and-a half-year-old Golden Retriever. The lymphomas started to spread all over his body very quickly and grew larger and larger as the days went by. It was aggressive cancer, and in a matter of two weeks he took a turn for the worse.
The vet was very plain and straightforward with us. Due to his age and other conditions that he already had, such as arthritis and neurological disorders, it was not worth making him go through chemo. That would have just prolonged his suffering, and he would have had a lot of side effects from it.
In the last few weeks, he slowed down a lot and stopped being himself. He could not stand on his own, he could not bark or breathe because the tumours on his throat prevented him from doing so; he couldn’t sleep through the night, he relieved himself inside the house, he did not want to eat, his eyes were sunken… We had to be home 24/7 to keep an eye on him. Watching him deteriorate was really heartbreaking. There was no point in suffering any longer.
Last week we set an appointment for Monday so we could have some days to say goodbye. In his last days, I didn’t leave home at all, only to take him out for his walks. We took lots of pics together (he hated taking pics!), slept with him, did his paw print and a cast, kept some of his fur and had lots of conversations with him.
I think he sensed his end was coming. We had such a hard time trying to take him to the vet because he did not want to leave home. I cried all the way to the vet. Watching him being euthanised was the most heart-wrenching thing I have ever experienced in my life. My mom was with me. My dad and my brother did not want to witness it. I knew I had to be there and there was no way I would let my baby leave this world without me being there. It’s the least I could do. I told him how much I loved him and thanked him for all the good years we’d spent together. I kissed and hugged him tightly throughout. What was most painful was when he kept staring at me once he had already crossed the rainbow bridge. I don’t know how I will ever be able to get the image of him seeing dead out of my head. It was devastating.
I'm 22, and he's been with me for more than half of my life. He was like a brother to me. Right now, I just don’t know how I will be able to move on… I am simply devastated. I couldn’t sleep tonight, and when I woke up I broke down again, seeing the house so empty without him around. I cried more when I grabbed his fur and smelt it. It feels so unreal. It has not sunk in yet. I've been trying to mentally prepare myself for this moment in the last year, but the truth is that you're never prepared for it...
I will miss his walks, seeing him go under the table waiting for food scraps to drop, following me around the house, seeing him greet me at the door when I get home, his barks asking for food… It will be a hard pill to swallow.
Luca, thank you for all these wonderful years full of love and joy that you gave us. You were more than a pet and a companion to me. You will be in my heart until the last days of my life. I will never forget you, I promise. I love you.

So I kinda fell down a rabbit hole with this one, but I want to share what I learned as I found the usual explanations of these two methods confusing and especially lacking in visual examples. Most people try to explain it with words and the idea behind it, but for me it did not really click until I actually saw the difference and played around with it. I also discovered something that might need to be changed in Godot when it comes to input (see the end examples).
If anything I say here is wrong, feel free to correct me. I base this off my understanding of what I have read so far and my own experiments, but I am by no means an expert.
Right, so, let's get to it.
In Godot you have two process methods.
_process() which runs once per frame with variable delta values depending on frame rate. _physics_process() which can run multiple times per frame with a fixed delta.
On ever frame, _process() runs first, then however many _physics_process() ticks needed to keep the target amount per second, up to a set maximum. The idea being that _physics_process() should try to run a fixed amount of times per second with a fixed delta value to keep things like physics and movement working correctly.
For example, with default settings, _process runs 60 times/second, and after each _process(), _physics_process() runs once. If the game starts to lag or slows down and you end up with say 30 fps, then _process() will run 30 times/second, while _physics_process() will still run 60 times as it now runs twice after each _process()
In short, _process() is what you see updated on the screen every frame, while _physics_process() can run checks multiple times, like position, in increments in between each frame.
That's the general explanation, but what does this actually mean in practical terms? What happens if you do it wrong and why does it matter? What would getting it wrong even look like? Let me show you.
In the editor, you can change some parameters to slow things down a bit so it is easier to see what is actually going on.
First, let's set "Max fps" to 1. This will force it to run at 1fps simulating some extreme lag.
https://preview.redd.it/8o6vkvbbcd0d1.png?width=874&format=png&auto=webp&s=8522169850db92f64fa413419049c4a01bd23964
This alone would in theory make _process() run once every second, and then 60 x _physics_process() calls after that. However, _physics_process() is limited by default to 8 per frame so it's just going to be 8. This is just to prevent running too many per frame which could cause it all to lock up, but it means that with 1fps it will never reach the target 60 with the default 8 max. However, the delta will act as if it does. As in, if the target is 60, but it only runs 8 times/second, the delta will still be 0.016666..7 and not 0.125 which 8 times/second would be. The "Physics ticks per second" dictates what the fixed delta will be, regardless of how many times it actually runs.
https://preview.redd.it/n60c0n8ncd0d1.png?width=858&format=png&auto=webp&s=4cf70ad972f5ac9f3d1dd0e26c1d394bdcbc8419
So there are several parts at play here. Fps, physics ticks per second, max physics steps (ticks) per frame and two different delta values.
A visualization of what a setting of 1fps, 60 physics ticks/second and 8 max per frame would look like:
https://preview.redd.it/3dth3mxibe0d1.png?width=1469&format=png&auto=webp&s=a92927c5ab0d5f95b2fd9f19152b2b3e6bc9e9c7
And what 1 fps, 8 physics ticks/second and 8 max per frame would look like:
https://preview.redd.it/4urmgd12de0d1.png?width=1209&format=png&auto=webp&s=650b82ed98e5ad68bd92e65cad124f5e3b455955
With that in mind, let's look at some examples.
First let's look at why it matters with some very simple movement. In the following example, it's just a character body moving to a point, stopping once distance is less than 10.
This is how it normally looks with 60 fps and 60 physics/sec. They move towards the target, and once close they stop at the same spot. This is intended behavior.
This is how it looks with forced 1fps and 60 physics/sec, but limited to 8 physics calls per frame. Notice how _process() no longer stops in the same spots and slightly overshoots. Also notice the over all slower speed, resulting a longer time to reach the target.
This is how it looks with forced 1fps and 8 physics/sec. Notice the change in speed due to delta now being spread over 1/8th instead of 1/60th. Also notice how _process() now never stops as it keeps overshooting the target, while _physics_process() still stops in the same spot as the original 60/60 example. Setting it to 1fps and 60 physics/sec with 60 max per frame would yield the same result as this.
So as you can see, there is a big difference in where the movement takes place.
Great! Then let's just put all the movement stuff in _physics_process()?
Well.. Not exactly.
Some things are only updated during _process() so using it during _physics_process() will not give you new values which might not give you the correct result. Among those is _input() and the Input singleton.
Keeping it at 1fps/8physics, let's look at an example where you move something from left to right by pressing right repeatedly.
Here the right key is spammed at approximately 7 times/second (around 40 key presses total). Notice that the movement is irregular and most of the key presses are missed and ignored. It only takes 3 registered key presses to reach the goal at this setting.
The important thing to note here is that unless the key is being pressed at the same time as _process() runs, it will not get registered.
There is an exception to this, and that is Input.is_action_just_pressed() which will register on the next _process() call, but only once.
For actually catching every input, use _input().
Here the right key is pressed only 3 times between frames, notice how none of them are missed. It moves 3 times in between the frames, but shows it as a single move on the next _process() call. Here I used Input.get_vector() but could have used the event.get_vector() as well, the result is the same.
_input() pools all the key presses in between _process() calls and runs them all in sequence on the next _process() call, before any _physics_process().
So to conclude:
Use _physics_process() only for things that move on their own or need to do things like position checks to keep consistency and accuracy. But if it involves anything that is only updated once per _process() put it elsewhere or in _process(), depending on what it is, like _input() for key presses. Putting too much in _physics_process() can also cause problems, so reserve it for only things that need to be there to work correctly.
I see many tutorials fetching input in _physics_process(), and even the default Godot template for CharacterBody and the official docs does it. However, based on this, that seems wrong, as input does not change between _physics_process() calls, and is only updated and checked once during _process() calls. Maybe this is a bug or not intended to work like this, but it does as of 4.2.1.
Under normal conditions, it should not make a considerable difference, but at very low (and possibly also high) frame rates it may impact accuracy, so worth keeping in mind.
Hopefully this will be helpful to someone else that also have a hard time wrapping their head around the difference between these two methods, what they actually do and which one to use for what. If not, I just wasted a bunch of time, heh.
At least I feel it makes a bit more sense to me now.

Art by Bob Nicholls
Nowadays, when we envision the words “prey,” among modern mammalian fauna, few taxa come to mind as quickly as the hoofed mammals, better known as the ungulates. Indeed, for the better part of their entire evolutionary history, the ungulates have become entirely indistinguishable from the term “prey.” Across their two major modern branches, the artiodactyls (the “even-toed ungulates,” such as bovids, pigs, deer, hippos and giraffes) and the perissodactyls (the “odd-toed ungulates,” including horses, rhinos and tapir), the ungulates too have created an empire spanning nearly every continent, establishing themselves as the the dominant herbivores throughout their entire range. However, as a price for such success, their lot as herbivores have forced them into an unenviable position: being the food for the predators. Indeed, throughout the diets of most modern predators, ungulates make up the majority, if not the entirety, of their diet, becoming their counterparts in this evolutionary dance of theirs. They have become the lamb to their wolf, the zebra to their lion, the stag to their tiger. If there is a predator in need of lunch, chances are that there is an ungulate there to provide it. Of course, such a dynamic is not necessarily a recent innovation. For the last 15-20 million years, across much of the world, both new and old, the ungulates have served as prey for these predators through it all. Over the course of whole epochs, these two groups have played into these roles for millions of years, coevolving with each other in an eons-long game of cat-and-mouse. The shoes they fill are not new, but have existed for ages, and within their niches they have cultivated their roles to perfection. Indeed, with such a tenured history, it seems hardly surprising the ungulates are wholly inseparable from the terms “prey,” itself.
However, while this is the case now, as it has been for the last 15-20 million years, go back far enough, and we see that this dynamic is not as set in stone as we would think. Indeed, back during the Eocene and Oligocene, during the very earliest days of age of mammals, things were very different for the ungulates. While today they are considered little more than food for modern predators, during these olden days, the ungulates weren’t quite so benign. In fact, far from being fodder for top predators, the ungulates had turned the tables, instead becoming top predators themselves. Indeed, though nearly unheard of today, throughout much of the Eocene and Oligocene, carnivorous ungulates thrived in abundance, developing specializations for catching large prey and establishing themselves as top predators that competed alongside the more traditional carnivores, and even dominating them in some instances. Given such success, it’s no wonder that multiple such clades had arisen during this time. Such predators included the arctocyonids, a lineage of (ironically) hoof-less ungulates with large jaws and sharp teeth for capturing large prey. There were also the mesonychians, a lineage of dog-like ungulates with massive skulls and jaws that allowed them to reign as the top predator across much of the Eocene.
However, among these various lineages, one stands stands out among the rest, by far. Arising during the Eocene, this lineage, though superficially resembling modern pigs, hailed from one an ancient lineage of artiodactyls far removed from swine or most other ungulates in general, with few close relatives alive today. Through perhaps not the most predatory of the bunch, it was among the most formidable, as their superficially pig-like appearance came with giant predatory jaws and teeth unlike anything from the modern era. And of course, as if all of that wasn’t enough, this lineage also went on to earn arguably one of the most badass nicknames of any lineage of mammals, period. These predators, of course, were the entelodonts, a.k.a the “hell-pigs.” More so than any other predatory ungulate lineage, these formidable ungulates were the ones to turn the current paradigm upside down, becoming some of the largest and most dominant carnivores in their landscape, even with (and often in spite of) the presence of more traditional predators. Through impressive size, fearsome teeth and sheer tenacity, these animals became the top dogs of their time, ruling as behemoth-kings of their Paleogene kingdoms, domineering all comers, and throughout the ranks, one entelodont in particular demonstrated such dominance the best. Though not the largest or most powerful of their kind, it is one of the most iconic, being among the most well-known members of its lineage to date. Moreover, this enteledont also has some of the most complete life histories ever seen out of this clade, with its brutality and predatory prowess being displayed in the fossil record in a way seen in no other member of its kind. More than anything else, however, it was this predator that best turned the notion of “ungulates being prey” on its head, living in an environment that bore some of the largest carnivoran hypercarnivores to date and still reigning as the undisputed top predator of its domain. This fearsome beast was none other than Archaeotherium, icon of the entelodonts, terror of the Oligocene American west and undisputed king of the White River badlands.
The rise of Archaeotherium (and of entelodonts in general) is closely tied to the ascendancy of carnivorous ungulates as a whole, one of the earliest evolutionary success stories of the entire Cenozoic. Having become their own derived clade since the late Cretaceous, the ungulates were remarkably successful during the early Paleogene, as they were among the first mammalian clades to reach large sizes during those early days after the non-avian dinosaurs had gone extinct. As such, it was with incredible swiftness that, as the Paleogene progressed, the ungulates swooped upon the various niches left empty by the K-Pg mass extinction that killed the dinosaurs. This of course included the herbivorous niches we would know them for today, but this also included other, much more carnivore roles. Indeed, early on during the Paleogene, it was the ungulates that first seized the roles of large mammalian predators, becoming some the earliest large mammalian carnivores to ever live, well before even the carnivorans. Such predators included the arctocyonids, a lineage of vaguely dog-like, hoof-less ungulates with robust jaws and sharpened teeth that acted as some of earliest large carnivores of the Paleocene, with genera such as Arctocyon mumak getting up to the size of big cats. Even more prolific were the mesonychids. More so than what pretty much any other lineage of predator, it was the mesonychids that would stand out as the earliest dominant predators of the early Cenozoic. Growing up to the size of bears and with enormous, bone-crushing jaws, the mesonychids were among the most powerful and successful predators on the market at that time, with a near-global range and being capable of subjugating just about any other predator in their environments. Indeed, they, along with other carnivorous ungulates (as well as ungulates in general), were experiencing a golden age during this time, easily being the most prolific predators of the age. Given such prevalence, it should be no surprise that there would be yet another lineage of predatory ungulates would throw their hat into the ring, and by early Eocene, that contender would none other than the entelodonts.
The very first entelodonts had arisen from artiodactyl ancestors during the Eocene epoch, at a time when artiodactyls were far more diverse and bizarre than they are now. Through today known from their modern herbivorous representatives such as bovines, deer, and antelope, during the Paleocene and Eocene, the artiodacyls, as with most ungulates of that time, were stronger and far more predaceous, particularly when it came to one such clade of artiodactyls, the cetacodontamorphs. Only known today from hippos and another group of artiodactyls (one which will become relevant later), the cetacodantomorphs emerged out of Asia around 55 million years ago, at around the same time that artiodactyls themselves had made their debut. These animals included the first truly predatory artiodactyls, with many of them possessing large skulls with powerful jaws and sharp, predatory teeth. Among their ranks included animals as puny as Indohyus, a piscivorous artiodactyl the size of a cat, to as formidable as Andrewsarchus, a giant, bison-sized predator often touted as one of the largest predatory mammals to ever live. Given such a predatory disposition, it wouldn’t be long until this clade produced a lineage of truly diverse, truly successful predators, and by around 40 million years ago, that is exactly what they did, as it was at that time that the entelodonts themselves first emerged. From their Asian homeland, the entelodonts spread across the world, spreading through not only most of Eurasia but also colonizing North America as well, with genera such as Brachyhyops being found across both continents. Here, in this North American frontier, the entelodonts began to diversify further, turning into their most successful and formidable forms yet, and it was around the late Eocene and early Oligocene that Archaeotherium itself had entered the scene.
Just from a passing glance at Archaeotherium, it is clear how exactly it (as well as the other entelodonts) earned the nickname of “hell-pigs.” It was a bruiser for starters; its body bore a robust, pig-like physique, with prominent neural spines and their associated musculature forming a hump around the shoulder region, similar to the hump of a bison. With such a bulky physique came with it impressive size; the average A. mortoni had a head-body length of roughly 1.6-2.0 m (5.3-6.6 ft), a shoulder height of 1.2 m (4 ft) and a body mass of around 180 kg (396 lb) in weight (Boardman & Secord, 2013; Joeckel, 1990). At such sizes, an adult Archaeotherium the size of a large male black bear. However, they had the potential to get even bigger. While most Archaeotherium specimens were around the size described above, a select few specimens, labeled under the synonymous genus “Megachoerus,” are found to be much larger, with skulls getting up to 66% longer than average A. mortoni specimens (Foss, 2001; Joeckel, 1990). At such sizes and using isometric scaling, such massive Archaeotherium specimens would attained body lengths over 2.5 m (8.2 ft) and would have reached weighs well over 500 kg (1100 lb), or as big as a mature male polar bear. Indeed, at such sizes, it is already abundantly evident that Archaeotherium is a force to be recorded with.
However, there was more to these formidable animals than sheer size alone. Behind all that bulk was an astoundingly swift and graceful predator, especially in terms of locomotion. Indeed, the hoofed feet of Archaeotherium, along with other entelodonts, sported several adaptations that gave it incredible locomotive efficiency, essentially turning it into a speed demon of the badlands. Such adaptations include longer distal leg elements (e.g. the radius and tibia) than their proximal counterparts (e.g. the humerus and femur), fusion of the radius and ulna for increased running efficiency, the loss of the clavicle (collar-bone) to allow for greater leg length, the loss of the acromion to enhance leg movement along the fore-and-aft plane, the loss of digits to reduce the mass of the forelimb, the fusion of the ectocuneiform and the mesocuneiform wrist-bones, among many other such traits (Theodore, 1996) . Perhaps most significant of these adaptations is the evolution of the “double-pulley astragalus (ankle-bone),” a specialized modification of the ankle that, while restricting rotation and side-to-side movement at the ankle-joint, allows for greater rotation in the fore-and-aft direction, thus allowing for more more powerful propulsion from the limbs, faster extension and retraction of the limbs and overall greater locomotive efficiency (Foss, 2001). Of course, such a trait was not only found in entelodonts but in artiodactyls as a whole, likely being a response to predatory pressures from incumbent predatory clades arising at the same time as the artiodactyls (Foss, 2001). However, in the case of the entelodonts, such adaptations were not used for merely escaping predators. Rather, they were used to for another, much more lethal effect…
Such notions are further reinforced by the entelodonts most formidable aspect, none either than their fearsome jaws, and in this respect, Archaeotherium excelled. Both for its size and in general, the head of Archaeotherium was massive, measuring 40-50 cm (1.3-1.6 ft) in length among average A. mortoni specimens, to up to 78 cm (~2.6 ft) in the larger “Megachoerus” specimens (Joeckel, 1990). Such massive skulls were supported and supplemented by equally massive neck muscles and ligaments, which attached to massive neural spines on the anterior thoracic vertebrae akin to a bisons hump as well as to the sternum, allowing Archaeotherium to keep its head aloft despite the skulls massive size (Effinger, 1998). Of course, with such a massive skull, it should come as no surprise that such skulls housed exceptionally formidable jaws as well, and indeed, the bite of Archaeotherium was an especially deadly one. Its zygomatic arches (cheek-bones) and its temporal fossa were enlarged and expanded, indicative of massive temporalis muscles that afforded Archaeotherium astoundingly powerful bites (Joeckel, 1990). This is further augmented by Archaeotherium’s massive jugal flanges (bony projections of the cheek), which supported powerful masseter muscles which enhanced chewing and mastication, as well as an enlarged postorbital bar that reinforced the skull against torsional stresses (Foss, 2001). Last but not least, powerful jaws are supplemented by an enlarged gape, facilitated by a low coronoid process and enlarged posterior mandibular tubercles (bony projections originating from the lower jaw), which provided an insertion site for sternum-to-mandible jaw abduction muscles, allowing for a more forceful opening of the jaw (Foss, 2001). All together, such traits suggest a massive and incredibly fearsome bite, perhaps the most formidable of any animal in its environment.
Of course, none of such traits are especially indicative of a predatory lifestyle. Indeed, many modern non-predatory ungulates, like hippos, pigs and peccaries, also possess large, formidable skulls and jaws. However, in peeling back the layers, it is found there was more to the skull of Archaeotherium that lies in store. Indeed, when inspecting the animal closely, a unique mosaic of features is revealed; traits that make it out to be much more lethal than the average artiodactyl. On one hand, Archaeotherium possessed many traits similar to those of herbivores animals, as is expected of ungulates. For instance, its jaw musculature that allowed the lower jaw of Archaeotherium a full side-to-side chewing motion as in herbivores (whereas most carnivores can only move their lower jaw up and down)(Effinger, 1998). On the other hand, Archaeotherium wielded many other traits far more lethal in their morphology, less akin to a herbivore and far more akin to a bonafide predator. For instance, the aforementioned enlarged gape of Archaeotherium is a bizarre trait on a supposed herbivore, as such animals do not need large gapes to eat vegetation and thus have smaller, more restricted gapes. Conversely, many predatory lineages have comparatively large gapes, as larger gapes allow for the the jaws to grab on to more effectively larger objects, namely large prey animals (Joeckel, 1990).
Such a juxtaposition, however, is most evident when discussing the real killing instruments of Archaeotherium — the teeth. More so than any facet of this animal, the teeth of Archaeotherium are the real stars of the show, showing both how alike it was compared to its herbivores counterparts and more importantly, how it couldn’t be more different. For instance, the molars of Archaeotherium were quite similar to modern herbivores ungulates, in that they were robust, bunodont, and were designed for crushing and grinding, similar in form and function to modern ungulates like peccaries (Joeckel, 1990). However, while the molars give the impression that Archaeotherium was a herbivore, the other teeth tell a very different story. The incisors, for example, were enlarged, sharpened, and fully interlocked (as opposed to the flat-topped incisors seen in herbivores ungulates), creating an incisor array that was seemingly ill-suited for cropping vegetation and much more adept at for gripping, puncturing and cutting (Joeckel, 1990). Even more formidable were the canines. Like the modern pigs from which entelodonts derived their nicknames, the canines of Archaeotherium were sharp and enlarged to form prominent tusk-like teeth, but unlike pigs, they were rounded in cross-section (similar to modern carnivores like big cats, indicating more durable canines that can absorb and resist torsional forces, such as those from struggling prey) and were serrated to form a distinct cutting edge (Effinger, 1998; Joeckel, 1990; Ruff & Van Valkenburgh, 1987). These canines, along with the incisors, interlock to stabilize the jaws while biting and dismantling in a carnivore-like fashion. More strikingly, the canines also seem to act as “occlusal guides,” wherein the canines help align the movement and position of the rear teeth as they come together, allowing for a more efficient shearing action by the rear teeth. This function is seen most prevalently modern carnivores mammals, and is evidenced by the canine tooth-wear, which is also analogous to modern predators like bears and canids (Joeckel, 1990). Indeed, going off such teeth alone, it is clear that Archaeotherium is far more predatory than expected of an ungulate. However, the real stars of the show, the teeth that truly betray the predatory nature of these ungulates, are the premolars. Perhaps the most carnivore-like teeth in the entelodont’s entire tooth row, the premolars of Archaeotherium, particularly the anterior premolars, are laterally compressed, somewhat conical in shape, and are weakly serrated to bear a cutting edge, giving them a somewhat carnivorous form and function of shearing and slicing (Effinger, 1998). Most strikingly of all, the premolars of Archaeotherium bear unique features similar not to modern herbivores, but to durophagous carnivores like hyenas, particularly apical wear patterns, highly thickened enamel, “zigzag-shaped” enamel prism layers (Hunter-Schraeger bands) on the premolars which is also seen in osteophagous animals like hyenas, and an interlocking premolar interface wherein linear objects (such as bones) inserted into jaws from the side would be pinned between the premolars and crushed (Foss, 2001). Taken together, these features do not suggest a diet of grass or vegetation like other ungulates. Rather, they suggest a far more violent diet, one including flesh as well as hard, durable foods, particularly bone. All in all, the evidence is clear. Archaeotherium and other entelodonts, unlike the rest of their artiodactyl kin, were not the passive herbivores as we envision ungulates today. Rather, they were willing, unrepentant meat-eaters that had a taste for flesh as well as foliage.
Of course, even with such lines of evidence, its hard to conclude that Archaeotherium was a true predator. After all, its wide gape and durophagous teeth could have just as easily been used for scavenging or even to eat tough plant matter such as seeds or nuts, as in peccaries and pigs, which themselves share many of the same adaptations as Archaeotherium, include the more carnivorous ones (e.g. the wide gape, using the canines as an occlusal guide, etc.). How exactly do we know that these things were veritable predators and not pretenders to the title. To this end, there is yet one last piece of evidence, one that puts on full display the predatory prowess of Archaeotherium —evidence of a kill itself. Found within oligocene-aged sediment in what is now Wyoming, a collection of various fossil remains was found, each belonging to the ancient sheep-sized camel Poebrotherium, with many of the skeletal remains being disarticulated and even missing whole hindlimbs or even entire rear halves of their body. Tellingly, many of the remains bear extensive bite marks and puncture wounds across their surface. Upon close examination, the spacing and size of the punctures leave only one culprit: Archaeotherium. Of course, such an event could still have been scavenging; the entelodonts were consuming the remains of already dead, decomposed camels, explaining the bite marks. What was far more telling, however, was where the bite marks were found. In addition bite marks being found on the torso and lumbar regions of the camels, various puncture wounds were found on the skull and neck, which were otherwise uneaten. Scavengers rarely feast on the head to begin with; there is very little worthwhile meat on it besides the brain, cheek-muscles and eyes, and even if they did feed on the skull and neck, they would still eat it wholesale, not merely bite it and then leave it otherwise untouched. Indeed, it was clear that this was no mere scavenging event. Rather than merely consuming these camels, Archaeotherium was actively preying upon and killing them, dispatching them via a crushing bite to the skull or neck before dismembering and even bisecting the hapless camels with their powerful jaws to preferentially feast on their hindquarters (likely by swallowing the hindquarters whole, as the pelvis of Poebrotherium was coincidentally the perfect width for Archaeotherium to devour whole), eventually discarding the leftovers in meat caches for later consumption (Sundell, 1999). With this finding, such a feat of brutality leaves no doubt in ones mind as to what the true nature of Archaeotherium was. This was no herbivore, nor was it a simple scavenger. This was an active, rapacious predator, the most powerful in its entire ecosystem.
Indeed, with such brutal evidence of predation frozen in time, combined with various dental, cranial, and post cranial adaptations of this formidable animal, it’s possible to paint a picture of how this formidable creature lived. Though an omnivore by trade, willing and able to feast on plant matter such as grass, roots and tubers, Archaeotherium was also a wanton predator that took just about any prey it wanted. Upon detecting its prey, it approached its vicim from ambush before launching itself at blazing speed. From there, its cursorial, hoofed legs, used by other ungulates for escape predation, were here employed to capture prey, carrying it at great speeds as it caught up to its quarry. Having closed the distance with its target, it was then that the entelodont brought its jaws to bear, grabbing hold of the victim with powerful jaws and gripping teeth to bring it to a screeching halt. If the victim is lucky, Archaeotherium will then kill it quickly with a crushing bite to the skull or neck, puncturing the brain or spinal cord and killing its target instantly. If not, the victim is eaten alive, torn apart while it’s still kicking, as modern boars will do today. In any case, incapacitated prey are subsequently dismantled, with the entelodont using its entire head and heavily-muscled necks to bite into and pull apart its victim in devastating “puncture-and pull’ bites (Foss, 2001). Prey would then finally be consumed starting at the hindquarters, with not even the bones of its prey being spared. Such brutality, though far from clean, drove home a singular truth: that during this time, ungulates were not just prey, that they were not the mere “predator-fodder” we know them as today. rather, they themselves were the predators themselves, dominating as superb hunters within their domain and even suppressing clades we know as predators today, least of all the carnivorans. Indeed, during this point in time, the age of the carnivorous ungulates had hit their stride, and more specifically, the age of entelodonts had begun.
Of course, more so than any other ettelodont, Archaeotherium took to this new age with gusto. Archaeotherium lived from 35-28 million years ago during the late Eocene and early Oligocene in a locality known today as the White River Badlands, a fossil locality nestled along the Great Plains and Rocky Mountains. Though a chalky, barren landscape today, during the time of Archaeotherium, the White River Badlands was a swamp-like floodplain crisscrossed with rivers and interspersed with by a mosaic of forests concentrated around waterways, open woodlands and open plains. As with most ecosystems with such a lush disposition, this locale teemed with life, with ancient hornless rhinos, small horse-like hyracodonts and early camels roaming the open habitats while giant brontotheres, small early horses and strange, sheep-like ungulates called merycoidodonts (also known as “oreodonts”) dwelled within the dense forests. Within this locale, Archaeotherium stalked the open woodlands and riparian forests of its domain. Here, it acted as a dominant predator and scavenger across is territory, filling a niche similar to modern grizzly bears but far more predatory. Among its preferred food items would be plant matter such as roots, foliage and nuts, but also meat in the form of carrion or freshly caught prey. In this respect, smaller ungulates such as the fleet-footed camel Poebrotherium, a known prey item of Archaeotherium, would have made a for choice prey, as its small size would make it easy for Archaeotherium to dispatch with its powerful jaws, while the entelodonts swift legs gave it the speed necessary to keep pace with its agile prey.
However, the entelodont didn’t have such a feast all to itself. Just as the badlands teemed with herbivores, so too did it teem with rival predators. Among their ranks included fearsome predators such as Hyaenodon, a powerful, vaguely dog-like predator up to the size of wolves (as in H. horridus) or even lions (as in the Eocene-aged H. megaloides, which was replaced by H. horridus during the Oligocene). Armed with a massive head, fierce jaws and a set of knife-like teeth that could cut down even large prey in seconds, these were some of the most formidable predators on the landscape. There were also the nimravids, cat-like carnivorans that bore saber-teeth to kill large prey in seconds, and included the likes of the lynx-sized Dinictis, the leopard-sized Hoplophoneus and even the jaguar-sized Eusmilus. Furthermore, there were amphicyonids, better known as the bear-dogs. Though known from much larger forms later on in their existence, during the late Eocene and Oligocene, they were much smaller and acted as the “canid-analogues” of the ecosystem, filling a role similar to wolves or coyotes. Last but not least, there were the bathornithid birds, huge cariamiform birds related to modern seriemas but much larger, which filled a niche similar to modern seriemas or secretary birds, albeit on a much larger scale. Given such competition, it would seem that Archaeotherium would have its hands full. However, things are not as they appear. For starters, habitat differences would mitigate high amounts of competition, as both Hyaenodon and the various nimravids occupy more specialized ecological roles (being a plains-specialist and forest-specialist, respectively) than did Archaeotherium, providing a buffer to stave off competition: More importantly, however, none of the aforementioned predators were simply big enough to take Archaeotherium on. During the roughly 7 million years existence of Archaeotherium, the only carnivore that matched it in size was H. megaloides, and even that would have an only applied to average A. mortoni individuals, not to the much larger, bison-sized “Megachoerus” individuals. The next largest predator at that point would be the jaguars-sized Eusmilus (specifically E. adelos) which would have only been a bit more than half the size of even an average A. mortoni. Besides that, virtually every other predator on the landscape was simply outclassed by the much larger entelodont in terms of size and brute strength. As such, within its domain, Archaeotherium had total, unquestioned authority, dominating the other predators in the landscape and likely stealing their kills as well. In fact, just about the only threat Archaeotherium had was other Archaeotherium, as fossil bite marks suggest that this animal regularly and fraglantly engaged in intraspecific combat, usually through face-biting and possibly even jaw-wrestling (Effinger, 1998; Tanke & Currie, 1998). Nevertheless, it was clear that Archaeotherium was the undisputed king of the badlands; in a landscape of hyaenodonts and carnivorans galore, it was a hoofed ungulate that reigned supreme.
However, such a reign would not last. As the Eocene transitioned into the Eocene, the planet underwent an abrupt cooling and drying phase known as Eocene-Oligocene Transition or more simply the Grande Coupure. This change in climate would eliminate the sprawling wetlands and river systems that Archaeotherium had been depending on, gradually replacing it with drier and more open habitats. To its credit, Archaeotherium did manage to hang on, persisting well after the Grand-Coupure had taken place, but in the end the damage had been done; Archaeotherium was a dead-man-walking. Eventually, by around 28 million years ago, Archaeotherium would go extinct, perishing due to this change in global climate (Gillham, 2019). Entelodonts as a whole would persist into the Miocene, producing some of their largest forms ever known in the form of the bison-sized Daeodon (which was itself even more carnivorous than Archaeotherium), however they too would meet the same fate as their earlier cousins. By around 15-20 million years ago, entelodonts as a whole would go extinct. However, while the entelodonts may have perished, this was not the end of carnivorous ungulates as a whole. Recall that the cetacodontamorphs, the lineage of artiodactyls that produced the entelodonts, left behind two living descendants. The first among them were the hippos, themselves fairly frequent herbivores. The second of such lineage, however, was a different story. Emerging out of South Asia, this lineage of piscivorous cetacodontamorphs, in a an attempt to further specialize for the fish-hunting lifestyle, began to delve further and further into the water, becoming more and more aquatic and the millennia passed by. At a certain point, these carnivorous artiodactlys had become something completely unrecognizable from their original hoofed forms. Their skin became hairless and their bodies became streamlined for life in water. Their hoofed limbs grew into giant flippers for steering in the water and their previously tiny tails became massive and sported giant tail flukes for aquatic propulsion. Their noses even moved to the tip of their head, becoming a blowhole that would be signature to this clade as a whole. Indeed, this clade was none other than the modern whales, themselves derived, carnivorous ungulates that had specialized for a life in the water, and in doing so, became the some of the most dominant aquatic predators across the globe for millions of years. Indeed, though long gone, the legacy of the entelodonts and of predatory ungulates as a whole, a legacy Archaeotherium itself had helped foster, lives on in these paragons of predatory prowess, showing that the ungulates are more than just the mere “prey” that they are often made out to be. Moreover, given the success that carnivorous ungulates had enjoyed in the past and given how modern omnivorous ungulates like boar dabble in predation themselves, perhaps, in the distant future, this planet may see the rise of carnivorous ungulates once again, following in the footsteps left behind by Archaeotherium and the other predatory ungulates all those millions of years ago.