66 million years ago, a giant asteroid slammed into Earth, dooming 75% of life on the planet to extinction (including the dinosaurs).
However, there's always that silver lining. The death of all those creatures left a void in the ecosystem that could be filled by the survivors, eventually evolving into the species we see around us today.
Scientists believe this is what happened to a group of fish called acanthomorphs. Fossil evidence shows a veritable explosion of new forms filling the open niches formerly occupied by wiped-out species. Acanthomorphs became a diverse group that fills today's oceans.
Read more about it here: https://www.sciencedaily.com/releases/2018/04/180417155615.htm