I thought this can be considered the oposite to the monkeys' walk which the most time that are on land are quadrupedals and sometimes they can stand bipedal, so now in this case I'm asking about a specie which is able to stand the most time in a bipedal and erected posture but change to quadrupedal walk without many problems, this unlike humans that yes, we can crawl and "gallop" on four limbs, but only for brief periods and really without many advantages for this.

My supositions were that get the facultative quadrupedal posture would help to little distance high speed run, because impulse the body with the hindlimbs would allow a jump that would later be cushioned with the forelimbs, another assumption is that maintaining a facultative quadrupedalism for short periods would release the vertical pressure of the spine, hips and knees during that time. But this is principally just for search a good working of a creature design.

So, I found that ther are many biomechanical problems with the correct working of a desing like this.

The first problem appears looking the hips' shape of different primate species and a hip from a fully quadrupedal mammal.

We can see that more quadrupedal primate, the chimpazee hip, is more similar to the dog hip, being long, narrow and flat while the human hip is shorter, wide and "bowl-shaped".

Then can be seen that the human spine does not flex like a quadruped would. But for this I thought, add some vertebraes would help, just Im not sure how many.

So what I am looking for is to identify other possible anatomical and biomechanical problems and their respective solutions to allow a humanoid with functional facultative quadrupedalism, being good enough to be in quadruped form as well as to be in erect bipedal form.

This question might be closely related with this other How much can be modificated the humanoid body plan and still being able to perform the high speed throwing?

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    $\begingroup$ I just know that when I try to walk on all fours, I tend to think my legs are too long (or my arms are too short) and my fingers and wrists too delicate. It's also annoying "looking up" all the time just to look forward. $\endgroup$
    – DKNguyen
    Commented Apr 9, 2021 at 6:05
  • $\begingroup$ @DKNguyen. Yeah, those are some comfort problems for the quadrupedal walk on humans, are those problems which I wana solve, I just can think in add some vertebraes, reduce a little bit the legs and extend the arms. I thought delicated hands are not so problematic because baboons, racoons and opossums walk on pretty skillful hands. $\endgroup$
    – Drakio-X
    Commented Apr 9, 2021 at 8:39
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    $\begingroup$ How the neck works will definitely be an important thing, since we theorize that the fact that our neck is supported mostly by the spine rather than by the neck muscles is one of the reasons looking up for long periods is uncomfortable, but also one of the reasons we could afford to grow the bigger (and heavier) brain and head it took to give us the "brain power" we have. For reference look at the many strategies theropods had to be able to have big heads without them being too heavy to support (and how tiny their brains were in comparison to their bodies in comparison to modern apes). $\endgroup$ Commented Apr 9, 2021 at 13:55

1 Answer 1


How about this:

enter image description here

Four arms.

The forward arms will probably be stronger. They're carrying the head.

The pelvis is smaller so that arms can take the weight. The neck is longer so the head can look ahead.

Make the wrists more muscular so they can withstand the pounding, and make the feet/hands padded on the bottom so they can take the grinding.

p.s You just gained two arms with hands.

  • $\begingroup$ would it still be able to stand and walk bipedal? $\endgroup$
    – Drakio-X
    Commented May 5, 2021 at 20:32
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    $\begingroup$ @Drakio-X, that's a big maybe. If it spends a lifetime working out its muscles. It would be like doing a head stand. Not impossible, but not the best mode for its body type. $\endgroup$
    – Len
    Commented May 6, 2021 at 0:22

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