American Vegas Cobras are desendents of King Cobras. They live in and on Sand Dunes.
1 day after people
Power goes off and all is dark.
2 Days After People
Inside the Circus Circus, the food that wasn't part of the zoo buffet is waiting to be consumed. Rats, mice, buzzards, roaches, bacteria, mold and maggots feast on it. As this happens, the snakes get fat and thrive those eating it.
6 Months After People
The last of the food has either eaten or rotted away. Animals like the elephants and lions leave. As the mice and rats leave, the cobras follow them. The King Cobras living at the Circus Circus Las Vegas close to escape.
10 years after people
The American Vegas Cobra begin to evolve from the former King Cobras who escaped from the Circus Circus Las Vegas. They kill some minor animals like ex-zoo meerkats.
Long term evolution
Due to being used to hot and dry climates, they easily adapted to living in the Ruins of Las Vegas. Despite competition from Rattlesnakes, they managed to survive and hunt escaped baby zoo animals to prevent Competition.