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I’m curious - does anyone with knowledge about animal/evolutionary biology think that predatory horses, akin to the Mares of Diomedes from Greco-Roman mythology, are plausible?

I’ve found tidbits of info saying that horses have been witnessed eating meat, but it was clear that these animals were starving and desperate. Could horses that eat mostly, or exclusively, meat, be possible?

Obviously, their biology would have to changed… but at what point would the creature be so different that it would no longer be, you know, a horse?

I know that predators tend to have forward-facing eyes, a body that is low to the ground, and (of course) sharp claws and/or teeth. Equids have none of these features.

Some people on this site asked this question about centaurs… but not normal horses.

Please help?

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    $\begingroup$ Warning, this video is a bit disturbing, but here is a horse eating a young chicken: youtu.be/jP6dvgo25Z8 . It's suspected that this behavior is to shore up specific nutrient deficiencies that result from a primarily herbivore diet. $\endgroup$
    – Dragongeek
    Nov 23, 2020 at 9:38
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    $\begingroup$ Horses from computer game The Elder Scrolls 5 Skyrim are predators, they track players' character using "forward-facing eyes". Also there are a lot of predators without "forward-facing eyes" - starfishes, chameleons (its eyes works independently), etc... $\endgroup$
    – vodolaz095
    Nov 23, 2020 at 10:43
  • $\begingroup$ Once upon a time, long before the advent of the Word Wide Web, there lived in France a great biologist named Georges Cuvier (pronounced /kyvje/, or roughly Kyoo-vyey in English spelling). He is widely considered the founding father of comparative anatomy, and is recognized as the first to recognize the principle of the correlation of parts... $\endgroup$
    – AlexP
    Nov 23, 2020 at 11:14
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    $\begingroup$ ... Horses have the wrong teeth for a predator, the wrong legs, the wrong feet, and the wrong digestive system. Their head is too high, their eye are placed incorrectly, and their stance makes them visible from a distance. On the other hand, they are superbly adapted for grazing on the vast grassy plains of Eurasia (and the Americas, too). Horses can and do eat a little meat, especially if it happens to be readily available, but everything in them is geared towards eating lots of grass. $\endgroup$
    – AlexP
    Nov 23, 2020 at 11:18
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    $\begingroup$ horses don't have to be starving to eat meat, most herbivores will eat meat if given the chance. $\endgroup$
    – John
    Nov 23, 2020 at 21:03

6 Answers 6

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Yes and no.

First horses will eat meat when they can, this is true of most herbivores. Deer have been observed eating birds. All but the most highly specialized vertebrates can digest meat because our bodies can break down our own tissue and digesting meat is much easier than digesting plant matter. They may not get everything from it a carnivore will get, but meat is such a high nutrient density food source it is still a large gain.

Can horses evolve into predators, Yes.

Predatory pigs and ungulates have existed and the bulk of the change was in the head and neck, they evolved tearing teeth and a jaw that can open much wider and a thicker neck to tear flesh otherwise they are not all that different from a undomesticated horse. Will they pass for a normal horse, only to someone who has never seen a horse before.

Can you feed normal horses nothing but meat, no

Their digestive system is too geared up for plants, while they might be able to derive enough nutrients from it, they will suffer a lot of gastrointestinal problems, without fiber their digestive system will develop blockages which tend to be lethal.

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    $\begingroup$ You just gave me the funniest image when you said gastro problems - I immediately thought of these huge terrifying beasts that roam the land, hunting humans, red eyes blazing, ripping flesh off bones - but also farting and shitting everywhere, all over everything with absolute abandon as they do it because they haven't gotten biologically used to their new addiction yet. Realise I am not adding anything just wanted to share. (;-D) $\endgroup$ Nov 23, 2020 at 23:57
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The hippopotamus, colloquially known as the "river horse" might be the first step in the evolution to your desired predatory horse.

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A horse could certainly evolve over time to become a predator, however it would require radical changes in their gut, dental structure, and general body plan (horses are terrifyingly fragile, not good for a predator) and they would most likely be outcompeted by other better adapted animals before they managed to evolve into predators.

The best chance to get a predator horse would be to terraform a moon and populate solely with horses as large herbivores (with just grasses and and some insect species and the like to keep the ecosystem working).

But at that point is it even really a horse anymore?

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  • $\begingroup$ undomesticated horse are not that fragile $\endgroup$
    – John
    Nov 23, 2020 at 21:07
  • $\begingroup$ Fair enough, I am no expert on horses so I was just going off of what I had heard $\endgroup$ Nov 23, 2020 at 23:44
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Maybe... but it would be a stretch.

As AlexP pointed out in comments, horses are not built to be predators. Large predators such as lions hunt by stalking their prey, which requires them to get low to the ground, and they have forward-acing eyes that give them a huge advantage in depth perception and other visual aspects of hunting. Horse's eyes are spaced for maximum situational awareness (read: keeping watch for things hunting them).

If they're going to hunt successfully without trading their mouths and hooves for a more canine/feline muzzle/teeth and paws, they're going to need to rely on group tactics instead, more like wolves. Also, if they're not going to be the size of wolves, they're going to need to eat a lot of meat. Even lions, the largest extent land predators¹, are smaller than horses.

So the only way I see this happening is if they hunt by surrounding and trampling their prey. This requires their prey to be smaller than them, somewhat stupid, and fairly abundant. So, if they live somewhere that is absolutely inundated with small, slow, stupid prey animals, it might be possible. However, it would be a challenge for any ecosystem to support the necessary density of animal life.

(¹ ...or maybe tigers; they're about the same. I'm not counting lion/tiger hybrids since they don't occur naturally.)

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    $\begingroup$ The largest extant terrestrial predator is either the Polar Bear or larger sub-spiecies of Brown Bear (The former is occasionally classified as a Marine Mammal due to it's primary prey, seals, requiring it to spend a greater deal of time in water. The latter has a wide range of sizes ranging from about the same weight as a Lion (~400) on the small end to the same size as the Polar Bear (~1590 lbs) and Polar Bears are more consistently big). $\endgroup$
    – hszmv
    Nov 23, 2020 at 16:40
  • $\begingroup$ Good point, though I'm not sure I want to count brown bears; isn't their primary meat source fish? OTOH, polar bears hunting seals (if they can catch them on land, anyway) seems pretty close to how I was envisioning predatory horses... $\endgroup$
    – Matthew
    Nov 23, 2020 at 16:44
  • $\begingroup$ Brown bears are omnivours (their diets consist of 10% meat... when you're on average 400-1500 lbs of healthy weight, being a picky eater is not ideal. They eat whatever the can get their hands on.). Polar Bears diet is about 90% by contrast (classifying them as Hyper-carnivors like all feline species). $\endgroup$
    – hszmv
    Nov 23, 2020 at 16:55
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    $\begingroup$ Hooved predators have existed, hooves has nothing to do with whether something can be a predator or not. $\endgroup$
    – John
    Nov 23, 2020 at 21:08
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    $\begingroup$ @John, not entirely true. Hooves make stealth ("slinking" along the ground, being silent) harder, which is going to affect such a critter's options for how it can hunt. Not to mention it's pretty hard to grab prey with hooves. That doesn't mean it's impossible to be a predator with hooves (which is what I said in my answer), but it's not irrelevant, either. $\endgroup$
    – Matthew
    Nov 24, 2020 at 14:17
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Definition of predatory 1a: of, relating to, or practicing plunder, pillage, or rapine b: inclined or intended to injure or exploit others for personal gain or profit.

Nothing in the definition that makes meat-eating a requirement.

Horses are by nature a herd animal, but they are also by nature territorial. As a herd animal, the males have a natural tendency to protect the herd hierarchy. As a territorial animal, they will defend their territory to the death. There is a reason why their stalls are made out of very thick, strong wood and heavy steel bars.

Our experience with horses is usually with domesticated, trained horses. Horses in the wild are another completely different disposition. They will tear any other interloper apart if it impedes on their territory. A human has no chance against a wild horse, no matter what the movies say. Any horse found in the wild, you are best advised to give them a clear berth, respect their territory, and never, ever trust them. They can be unpredictable, ferocious and viscious. A herd of them is extremely dangerous. And a hose bite will take your hand off, or crunch the bones in an arm.

Even a domesticated horse is entirely capable of killing another horse it sees as a competitor or threat, depending on the herd hierarchy.

So yes, any wild male horse is to be considered as a predatory animal. Even a domesticated horse that has been abandoned in the wild and forced to survive on their own will become predatory. To keep a male horse domesticated, depending on the breed, it needs to be constantly told 'who's boss' by the trainer/rider/owner.

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A horse with a Narwhal like tooth adaptation would be able to hunt small prey by knocking them unconscious prior to eat it.

Squirrels/Iguanas would be good prey for them.

Ie : unicorns

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    $\begingroup$ Real unicorns aren't predators either... and there are still several issues. First, being able to move fast enough to hit a small critter like that at all, and being able to do it with an appendage that is poorly situated for said task. Something sticking straight out would work better for aiming, but then it interferes with getting food to the predator's mouth. Antlers might work better, just because the multiple points increase the chances of being able to connect, but there's a reason I said "slow and dumb" in my answer. $\endgroup$
    – Matthew
    Nov 23, 2020 at 16:28

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