It is estimated that there were less than 15,000 species or different kinds on the ark and that only had to include “mammals, birds, reptiles, and possibly land-reproducing amphibians.”
It is estimated that of those types of animals, there are only 30,000 living species today. So those animal types only needed to double in species. This is very possible to do in only a few thousand years, especially with artificial breeding programs. For example, “most dog breeds have been developed in the last 200 years.”
And we know that mutts have more genetic potential than purebred dogs. So God likely took “Supermutts!”
“God chose the animals to be saved and it is likely that the choice of animal was based on the genetic potential to produce a variety of animals after the Flood. God is the omniscient genetic engineer who chose each animal and made the variation in extant animals possible from all the animals on the Ark.
For more details on this: https://www.icr.org/article/speciation-animals-ark/