The biblical word «genus» is equal to the concept of «family» in the animal classification of the present
Noah did not need to find a place for fishes, softbodied, echinoderms, larvae, coelenterates, protozoa and those that could survive outside the Noah's ark
There were no lions or tigers on Noah's ark. Instead there was one pair of the genus
«And of every living thing of all flesh you shall bring two of every sort into the ark, to keep them alive with you; they shall be male and female. Of the birds after their kind, of animals after their kind, and of every creeping thing of the earth after its kind, two of every kind will come to you to keep them alive»
Horse family (lat. Equus)
Family Iguanas (lat. Iguanidae)
The felines (lat. Felidae)
It was necessary to take two individuals, and they would spread over the whole earth, coming down from Noah's ark
The feline family (lat. Felidae)
The canine (lat. Canidae)
John Woodmorapp counted some 8 000 genera, including, among others, extinct animals
The dog genus has an enormous variety of shapes and sizes. Think of the tiny Maltipoo and the huge Great Dane
Every creature for a pair, so there must have been only 16 000 on the Noah's ark
38 living and 36 extinct cats descended from her: domestic, stray and sabre-toothed tiger
Add to this list coyotes, wolves, dingoes, jackals, extinct Hesperocionines and borophagines, and by new research on foxes
It was also logical to take the babies on board the ark, who took up less space and did not need mother's milk
This is a sensible move first and foremost because:
The cubs survive the stress of being on the ark more easily
Once on land, they'll have more offspring