Using the Search on JWN could yield some extensive discussions on this Bells. Here's some quotes from WT publications (remember just reporting not supporting) Checking on the internet for non-jw, non-religious sites could add a new dimensions.
*** it-1 p. 327 Flood of Noah’s Day ***
Could the Ark Have Held All the Animals?
It is true that encyclopedias refer to over a million species of animals. But Noah was instructed to preserve only representatives of every “kind” of land animal and flying creature. Some investigators have said that just 43 “kinds” of mammals, 74 “kinds” of birds, and 10 “kinds” of reptiles could have produced the great variety of species of these creatures that are known today. The ark had about 40,000 cu m (1,400,000 cu ft) of usable space—ample for the passenger list
*** it-1 pp. 164-165 Ark ***
Ample Carrying Capacity. The passenger list of the ark was quite impressive. Besides Noah, his wife, his three sons, and their wives, living creatures “of every sort of flesh, two of each,” were to be taken aboard. “Male and female they will be. Of the flying creatures according to their kinds and of the domestic animals according to their kinds, of all moving animals of the ground according to their kinds, two of each will go in there to you to preserve them alive.” Of the clean beasts and fowls, seven of each kind were to be taken. A great quantity and variety of food for all these creatures, to last for more than a year, also had to be stowed away.—Ge 6:18-21; 7:2, 3.
The “kinds” of animals selected had reference to the clear-cut and unalterable boundaries or limits set by the Creator, within which boundaries creatures are capable of breeding “according to their kinds.” It has been estimated by some that the hundreds of thousands of species of animals today could be reduced to a comparatively few family “kinds”—the horse kind and the cow kind, to mention but two. The breeding boundaries according to “kind” established by Jehovah were not and could not be crossed. With this in mind some investigators have said that, had there been as few as 43 “kinds” of mammals, 74 “kinds” of birds, and 10 “kinds” of reptiles in the ark, they could have produced the variety of species known today. Others have been more liberal in estimating that 72 “kinds” of quadrupeds and less than 200 bird “kinds” were all that were required. That the great variety of animal life known today could have come from inbreeding within so few “kinds” following the Flood is proved by the endless variety of humankind—short, tall, fat, thin, with countless variations in the color of hair, eyes, and skin—all of whom sprang from the one family of Noah.
These estimates may seem too restrictive to some, especially since such sources as TheEncyclopediaAmericana indicate that there are upwards of 1,300,000 species of animals. (1977, Vol. 1, pp. 859-873) However, over 60 percent of these are insects. Breaking these figures down further, of the 24,000 amphibians, reptiles, birds, and mammals, 10,000 are birds, 9,000 are reptiles and amphibians, many of which could have survived outside the ark, and only 5,000 are mammals, including whales and porpoises, which would have also remained outside the ark. Other researchers estimate that there are only about 290 species of land mammals larger than sheep and about 1,360 smaller than rats. (TheDelugeStoryinStone, by B. C. Nelson, 1949, p. 156; TheFloodintheLightoftheBible,Geology,andArchaeology, by A. M. Rehwinkel, 1957, p. 69) So, even if estimates are based on these expanded figures, the ark could easily have accommodated a pair of all these animals.
