Evolution of Centaurs & Related Species

Contrary to popular belief, the centaurian species and it's subspecies are more closely related to arachnoids than humans or horses. Both developed humanoid upper bodies to act as 'lures' for other sapient species, but the difference lies in how those lures were utilised and adapted. Centaurs developed a symbiotic relationship with Atlas's humanoids whereas arachnoids are more predatory if not outright parasitic (note that some arachnoid colonies have claimed to 'set aside' their natures in favour of symbiosis).

While centaurs have evolved to appear mostly mammalian, even going so far as to reproduce via live births, some traces of their origins still remain. Most notably in the form of a fourth set of vestigial limbs located on the front of their thorax and between the ambulatory forelimbs (the front legs of the horse part). These limbs are limited in their uses, mostly relegated to holding things and keeping hold of their young.

Another relative of centaurs is the mantid species: large sapient praying mantis people who are rarely seen in Atmos, and arguably more dangerous than both centaurs and arachnoids in terms of sheer brutality.