unknown creature, far future
Quinary Epoch Giant Spermatozoon (Sperma colossus)
In the absence of apex predators, Quinary Megafauna grew to such massive sizes that heterosexual reproduction between gendered individuals became physically impossible.
Asexual reproduction developed as an adaptive evolutionary response in which male spermatozoa transformed into self-viable homunculus offspring with extraordinary fitness. The massive numbers of megasperm within each semen ejaculant, and the unrestrained self-sexual activity in the absence of a need to secure female mating partners, resulted in an unsustainable population spike of gendered Megafauna and the consequential extinction of the Quinian Megafaunal species soon after.