i think that the stalker probably developed legs Just cause it wanted to. Like That Fish did so long ago that started the evoloution of everything. The big frozen leviathan suggests that on ths Planet that sub zero takes place on used to be Mostly land and super green. Wgen the ice age pr watever started the stalker was rpabobly just like Oh well i want to stay here. And it grew fur

Ive never played either subnautica btw I just watched like two hours worth of youtube videos about its biology (its awesome . I ****ing love biology