to me, it seems like achieving this kind of arrangement would first require a reversed quadruped (belly up instead of belly down), which seems problematic for all sorts of reasons, and i’m not sure how you would transition from an existing quadruped to a reversed quadruped…
it seems to me like any path to reversed bipedalism would require a redesign of the head and neck first. i think you basically would have to eliminate the neck and merge the head into the torso to make it reasonable to even begin a transition to reversed bipedalism.
Giving this more thought than I should have here is a way we could get a probability estimate from the only experiment that we are aware life has run. For the purposes of this thought experiment I am assuming the development of bipedalism requires at least four limbs for the piped’s ancestors.
Find the total number of quadrupedal species that have resulted in bipedal species and place it over the total number of quadrupedal species that have ever existed. Let’s call that our quadruped to biped conversion base rate. Then do the same for all known reverse bipeds so we have a reverse bipedalism conversion rate. Compare the two.
To be fair we should be willing to consider the possibility that an already bipedal species could start using its opposite pair of limbs and we add those to the reverse bipedalism conversion rate.
I’m no expert when it comes to evolutionary biology so I can’t reliably calculate the quadruped to biped conversion base rate but I am guessing it is pretty low. The total reverse bipedalism conversion rate (plus biped to reverse biped) rate is still zero though.
Am I willing to say it is impossible? No. It is a big universe out there and we still know very little. Is it plausible? Not with the evidence we have.
I’m no expert on this, but as I understand it they use both pairs of limbs on the ground, but the hind limbs are so small and graspy that most of the movement comes from the wings.
It’s an ambush predator based off of a flounder and a lindworm. The only use its back legs have is too help bury itself in the sand. When it moves to a new location, it runs very quickly using its front limbs.
I’ve just come across a picture of Mexican Mole Lizard, Bipes biporus. It has front legs and no back leg. Moles(Mammals) have better developed front legs too.
seals, walruses, and whales have reduced back limbs, too, but i wouldn’t describe them as bipedal, nor do they strike me as future ancestors of reversed bipedal animals, but i guess we’ll know more in a million years…
Yes, I quickly found a couple more YouTube videos of dogs walking on their front legs. In the two cases, each dog was born with a birth defect which rendered their hind legs unusable or mostly absent. I doubt if any dog breeder would be interested in attempting to propagate such animals, so even if the birth defects were heritable, human selection is very unlikely to result in the creation of a new anterior-bipedal pooch. The infusion of a lot of human attention and kindness is the main reason those two dogs even survived. In nature, natural selection would probably act strongly against such a mutation spreading in a population of quadripeds.
That is the most plausible idea I’ve seen but I don’t think the rear limbs would last. The front limbs and the tail/head could also be used to cover the body with sand just as effectively.
Well, this conversation got into a lot more configurations than the one I had in mind.
I think that is it. The Dugs have a vertical, head-up posture, like we do; I wasn’t expecting the discussion to go to inverted (head-down) postures or horizontal postures like those dogs. I was trying to describe a basically human-like posture – head on top, bottom at the bottom – with long arms extending to the floor and short legs, sort of like chimpanzees, but the differences in limb length even more so.
Marina’s cartoon got the posture and skeletal structure I was thinking of, except that I was thinking of the forelimbs outside the body.
i think it would be fun if modified bat wings allowed for bipedalism… then beyond that, each of the fingers developed into individual limbs – 10 in total… so that such an evolutionary trajectory could get you to your dream of a tetrapod evolving to have more than 4 limbs…
i think it would retain its original hind feet just for grasping, but then the original fingers would effectively each be limbs, too… so effectively 12 limbs altogether. i don’t know how to label such a thing, dodecapod? (but decaped?)
A herbivore that spends its whole life wading in water eating plants. Its hind legs are small and used to grasp plant parts; its mouth is right above them. Its fore legs are long and stilt like, and covered in spikes to deter predators. I have no idea why/how this would evolve, though.
