...and of beasts that are not clean by two, the male and his female.
Genesis 7:2
"In April 2014, a male ‘zonkey’ with a donkey father and zebra mother was born at a Mexican zoo—an indication that such animals are descendants of an originally created horse (equine) ‘kind’ (Genesis 1:25).
This means Noah didn’t need to take on board the Ark two zebras, two donkeys, two Shetland ponies, etc.—rather, he only needed two ‘horses’ (Genesis 6:20)." CMI