Are hoofed bipeds feasible?

Question

Satyrs, fauns, pan, and even the devil are commonly depicted as humanoid bipeds with goatlike unguligrade hooves for feet. However, common as such beings may be in fantasy and mythology, I have been unable to unearth any paleontological evidence that any form of biped has ever had hoof-like feet.

There are, of course, examples of digitigrade bipeds, like kangaroos and ostriches, but they all have one common trait in common with one another: toes. That is to say, they all walk on their intermediate tarsals, leaving an additional tarsal at the end for balance and support. Hoofed, unguligrade animals don't have this sort of support, walking instead only on the distal-most tarsal in the foot.

For a quadruped, this isn't an issue, as there are plenty of other limbs to help maintain balance, but what about for a biped? Could a hoofed, unguligrade biped actually evolve, or can they only exist in fairy tales?

Answer 1

Absolutely

The digitigrade leg formation (with the foot acting a a third joint) was scientifically explained here, answers there may be useful to you, especially regarding balance. But you ask for unguligrade, where to toes act as a foot and the foot acts as a third joint. Keep in mind that, while when we think of unguligrades, we think of goats, cows or horses. But remember that rhinos, hippos and elephants are also all unguligrades, though the lack of mobility in their feet cause the same problem. They even make the problem of stability even worse.(Try pushing against a wall with your arm, one straight and one slightly bent; which one buckles first? As you can imagine, the straighter, the more stable)

The evolution aspect can be explained similar to primate evolution. All that is need is for your unguligrade quadrupeds eat fruit and scavenge meat and not grass or leaves. These omnivorous "proto-fauns", as I'll call them, would benefit from getting the most fruit and meat, but lets say instead of evolving longer necks (a la giraffe), as longer necks would actually be bad for the meat eating part of the omnivorous diet, they evolve hooves with multiple toes. Like a Mesonychid, used for hunting and for better gripping, allowing them to get higher in the tree.

Recently I have found an artist known as Russell Tuller, who works to create anatomically realistic anthropomorphic animals people. Primarily Wolves and Hooved animals. This design can be applied to your question;

Luckily unlike humans we do not have to explain why they left the jungles as they started in the Savannah already as our Proto-faun. At this point they would be more like chimps, not purely biped but close. Again we will introduce a section of human evolution here, they become purely bipedal unguligrade style legs in order to become more efficient long distance runner and you're done.

For these legs, you would want two features to separate it from the upper limbs

1. The toes become more splayed in order to take the weight, appearing more like digitigrade than unguligrade (though this is only an illusion of appearance). Similar to hand design seen above, but with much shorter digits.
2. The legs need to be as straight as possible while stile being unguligrade style. This allows them to have all the advantages of unguligrade while still having the long distance efficiency of humans (though not as efficient). An example would be similar to how a deer looks when standing.

Now the only problem to deal with is making the upper body more human. There are two things we need to consider here,

1. The fingers. It is unlikely and hopeless to believe that a perfect human hang could even, but a psudeo-hand made from the hoof can exist as pointed out above. This "hand" would have two fingers and two thumbs, ending in small hooves. To make the classic satyr, we want to remove the hoof and have pure skin fingertips. This can only be justified by saying that hoof fingertips are not necessary and thus they either stay as a result of genetic drift or they dispensary as a waste of resources.
2. The face. If you want a 100% pure human face, you're going to be out of luck, you are at best going to have a equine face that gets progressively flatter, but a primates face is really out of the ball park. Over a few million years, you can get close though. Artist JayRock on Tumblr has a good centaur design whose face seems close to what you might be able to eventually get,

Answer 2

The biggest problem with standing on two legs is keeping your balance when standing still. We humans solve this with our feet. Try standing still without leaning on something and pay attention to what the muscles in your feet are doing. You are always subconsciously adjusting your weight distribution along your feet to keep your balance. This is also why all bipedal creatures you found have toes, they are an essential part of that balance-keeping. The absence is seen with people walking on stilts. Since they can't control their weight distribution along their feet, they have to keep their balance by constantly taking steps. A person on stilts never stands still unless holding onto something else for balance, if they try then they fall over pretty quickly.

As for having a bipedal hooved creature, I see two solutions: modifying the hooves to have the equivalent of toes, or just not standing still. If the hooves are split and the different parts can shift around, this can be used as some kinds of makeshift toes to keep balance. See TrEs-2b's answer for how this might look, though perhaps not as extreme. If you instead want to keep a solid hoof, you could have them always be on the move while standing up. As soon as they stop they either sit down like in your picture or grab on to something for balance (perhaps each other). They would have to have leg muscles like springs to be able to shift between sitting and walking constantly and quickly, but it's not too far-fetched.

Answer 3

There are deer species in Africa that stand up and stretch their forelegs out, they always looked like they might evolve further someday:

Answer 4

No

Obligate bipedal ungulates are extremely unlikely to occur (evolve) naturally for a very clear reason.

The Problem Of Speed

Goats, deer and other such medium sized ungulates can stand (and also walk for short distances) on two legs. They usually do this when trying to reach higher foliage of trees. Several species of mountain goat also tend to get bipedal during male head-butting competitions.

However, there is no exception to the rule that bipedal ungulates walk very slowly on two legs as compared to their speed on four legs. You would never see a deer running for its life on two legs.

But what about the ungulates which don't need to run in front of predators? Buffaloes and bison; these large ungulates use their massive heads for their defense. When standing on two legs, they would be unable to use their heads for defense and they would also be exposing their vulnerable underbellies to the predators. No, that is not going to work.

Some might argue that once ungulates turn obligate bipeds, their physiology can evolve for higher speeds. That is not a valid argument. In order to evolve for higher speeds, these ungulates must survive long enough (a few hundred thousand years at least) to first become compulsory bipeds. Currently the life expectancy of a compulsory bipedal deer is less than a day. It does not seem likely that tigers, cheetahs and leopards would cherish the sight of a clumsy, bipedal deer enough to not invite it on their dinner tables.

The morphological changes from quadruped to biped stance are immense and include (but not limited to), changes in the backbone, in the skull features (specially where the brain connects to the spinal cord), in the leg joints, in the heel joints, in the shoulder joints and also in teeth and jaw structure.

Why Humans Survived The Change And Ungulates Wouldn't?

We humans made the successful transition from quadrupedal to bipedal gait but ungulates cannot. The simple reason is that we humans never relied on speed to evade (or defeat) predators. Since the time of Sahelanthropus (7 million years) to modern humans (0.2 million years ago), we have always relied on our superior brains, dexterity of our hands and supreme communication skills for survival.

On the contrary, ungulates have neither of these. Their mental skills are by no means any superior to their predators, they cannot even pick up a twig from the ground with their hands and they cannot even count from 1 to 5. During our early evolution, when a sabertooth attacked our great great forefathers, it only took them one vertical leap and some quick hand motions to reach the shelter of the branches. No such option is (or was) available to the ungulates. They would not able to make it.

Remember the terror birds of South America? They were bipedal and they were much better runners (like most flightless birds) than humans (we have evolved completely for bipedal gait and our running speeds are higher than any and all other bipedal mammals). Yet those awesome carnivorous birds were exterminated by mammalian carnivores of North America. How much prayer can a bipedal deer have against a ravenous cheetah?

The Incentive Of Height And Why It Would Not Work

Another (purely theoretical) argument for evolution of compulsory bipedal ungulates can be that of height and reach. Clearly, a bipedal deer would have greater reach than its quadrupedal cousin. In times of famine this could turn into the decisive variable between starvation and survival. If the famine lasted for a long time, a species of obligate bipedal ungulate could evolve.

This assumption is based on faulty logic. First, our planet has been through some seriously severe famines during its history and none of them has resulted in bipedal ungulates. Second, most ungulates are grass-eaters, not foliage-eaters and their diets primarily consist of grass species. Third, even if somehow some species of bipedal ungulates do evolve, they would be quickly devoured to extinction (due to slow speeds) by the carnivores once the famine ends and carnivorous populations re-establish.

Instead of bipedalism, mammalian evolution for longer reach has always resulted in longer necks. The giraffe and camel are the best examples for this.

Conclusion

No, bipedalism is extremely unlikely (we never say never in science) to evolve or have evolved during the history of mammals. The only time it could have evolved and remained was during the origin of mammals, some 221 million years ago. However, once the general mammalian body shape was established firmly by late Jurassic, the transition from quadrupedal to bipedal gait was too risky and dangerous (not to forget without any real rewards or incentives) for any mammalian group.

Humans were able to successfully transition from arboreal to obligate bipedal lifestyle because we never relied on speed for survival. We had higher intellect, dexterous hands and superb communication skills to help us win against predators. Current (or prehistoric) ungulates never had these abilities to bail them out against predators, so they cannot survive the transition.

Answer 5

This may be a bit late but I do feel the need to mention the fact that this is definitely possible, because it has already happened!

Slijper's goat was born with no fore limbs. It seems to have been well able to walk and run around as it pleased. It died accidentally (apparently) at a year old and Slijper dissected it. It showed a fascinating array of variations in physiology compared to the usual quadrapedal goat, simply due to developmental plasticity. I'd suggest you look into it yourself for more details rather than me just copying and reposting information.

If a normally quadrapedal animal can adapt in such a manner through no real genetic change, I think an animal that is actually adapted to bipedality through evolution is entirely plausible.

The original scientific paper referencing this goat is as follows, though I have unfortunately been unable to find it online anywhere myself. Most frustrating.

Slijper E. J. 1942. Biologic-anatomical investigations on the bipedal gait and upright posture in mammals, with special reference to a little goat, born without forelegs. Proceedings of the Koninklijke Nederlandse Akademie Van Wetenschappen 45, 288-295, 407-415.

Answer 6

Simians evolved arms and hands to facilitate brachiating and although humans can still climb we've clearly developed away from our branch swinging roots. Now I have trouble imagining cloven feet being useful in the trees but in thick underbrush having feet that can penetrate the foliage and be retracted without becoming entangled would be advantageous. So I imagine something like a faun would be the product of a densely forested area with thick underbrush, perhaps even using its hooves like spikes to assist in vertical climbing.