Unknown Story

There is a mix of short-tailed and long-tailed alligators on an island
A water current swept a mix of short-tailed and long-tailed alligators to another island, which was too far to swim from the original island.
The island caught on fire due to the hot temperature, and only the alligators with the long tails were able to swim away safely because they could swim faster
After the island cleared up, only the alligators with the long tails remained to reproduce with each other and keep the population alive
After years of only having long-tailed alligators on the island, the mating signals started to change to where long-tailed alligators could only understand certain signals. This meant that when the short-tailed alligators and long-tailed alligators came together, they wouldn't undertand each other.
When the two populations came together, the original alligators attempted to reproduce with the long-tailed alligators on the island but were unsuccessful due to different behaviors. After spending so much time with each other, the long-tailed alligators developed their own communication and mating signals that were foreign to the alligators on the original island. They were behaviorally isolated and couldn't reproduce with each other