Why would a biped evolve into a monoped?

Say that you have a medium-sized, bipedal, vertebrate-like creature. It no longer has the need to have arms, so they atrophied until they disappeared entirely.

Now imagine an animal that shares similar morphology to the other one, except that its two legs have, over time, fused to become a single, muscular leg. It is saltatorial, hopping across its open habitat like a kangaroo.

How would this evolutionary transition occur? What need would a two-legged animal have to fuse its legs into one? I'd prefer if answers weren't "the common ancestor had a birth defect and became genetically isolated", but rather something of an explanation as to how monopedalism would become advantageous to something.

posted over 5 years ago

SealBoi‭

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