A World Stuck In The Past

Primordia has no records of any history, as the most advanced and intelligent species on the planet is a variant of Homo Sapien that has no forms of record keeping, hunt with spears and arrows, and paint on cave walls with their fingers.   Aside from these more primitive humans, no other form of sapient life exists. It truly is a primal world, filled with ancient creatures ranging from Early Cambrian vertebrates, to indomitable, and noticeably prevelant dinosaurs from the Mesozoic, and finally, the vaguely familiar, but iconic furred animals from the Pleistocene.   It is a mystery as to why these creatures from vastly different time periods exist in the same world as one another, and most shockingly, live comfortably with the oxygen and atmospheric pressure that allows our ancestral relatives to live on Primordia without issue.