1. Climate change: Shifts in climate and vegetation due to natural factors (such as changes in global sea levels and increased aridity) and/or human activities (like fires and habitat modification) are significant contributors to megafauna extinction.
2. Human hunting: As humans dispersed across the globe, they often preyed upon large animals for food and resources (i.e., overhunting/overkill). Evidence for human predation often takes the form of spear marks and cut marks on animal bones found at archaeological sites.
3. Competition: In some cases, the introduction of more adaptable domesticated large animal species (such as cows and horses) may have outcompeted megafauna species for grazing grounds and other resources.
4. Infectious diseases: Disease transmission from domesticated animals to previously isolated megafauna can also devastate their populations due to a lack of prior exposure and immunity to such pathogens.
Ultimately, it is vital to acknowledge the intricacy of such factors as numerous species vanished during different temporal intervals and varied geographic regions during the Pleistocene (2.6 million years ago - 11,700 years ago). It is, therefore, challenging to identify just one cause, likely a series of interacting ones that led to the disappearance of numerous colossal beasts from our realm.