#001: Bulbasaur
Roughly 65 million years ago, the majority of all life on earth died out. This was thought to be the result of a meteor or unknown space-faring pokemon colliding with the earth, throwing up clouds of dust so thick that the sun was obscured. No sunlight meant no photosynthesis, which kick-started a cascade of extinction as complicated, co-dependent food webs quickly unravelled.
But a few decades ago, the discovery of a Bulbasaur-predecessor in the fossil-record caused major upset. The Bulbasaur line was already known to be one of the most ancient plant/animal hybrid pokemon in existence, but this new evidence revealed that the symbiosis between plant and animal began to appear around the same time as the extinction event. This startling revelation led to further investigation, and over the years more and more grass-type pokemon, from Tropius to Chikorita, have been found to originate from this period. As evidence mounted up, it became an unavoidable conclusion: the sun could not have been blotted out if merging with plants aided survival rather than hindering it.
Instead of a desolate wasteland, the 'Paleocene' epoch is now believed to have been abundant in plant life and grass pokemon. Though recognised as one of the most important developments in palaeontology, this discovery has left a worrying gap in our knowledge. We no longer know what caused so many pokemon to die out.
In the 21st century, the remarkable 'Helix' technology has allowed a handful of ancient species to be recovered, yet humanity is still no closer to solving this mystery. It has been noted, however, that in every successful case, the resurrected pokemon display an inexplicable fear of grass-type attacks.