John Woodmorappe, author of the definitive Noah's Ark: A Feasibility Study, estimated that only about 15% of the animals on the ark would have been larger than a sheep. This figure does not take into account the possibility that God may have brought Noah “infant” animals, which can be significantly smaller than adult animals.
How many animals were on the ark? Woodmorappe estimates about 16,000 “kinds.” What is a “kind”? The designation of “kind” is thought to be much broader than the designation “species.” Even as there are 400-something dog breeds but they all belong to one species (Canis familiaris), in the same way many species can belong to one kind. Some think that the designation “genus” may be somewhat close to the Biblical “kind.”
Nevertheless, even if we presume that “kind” is synonymous with “species,” “there are not very many species of mammals, birds, amphibians and reptiles. The leading systematic biologist, Ernst Mayr, gives the number as 17,600. Allowing for two of each species on the ark, plus seven of the few so-called “clean” kinds of animals, plus a reasonable increment for known extinct species, it is obvious that not more than say, 50,000 animals were on the ark.” (Morris, 1987)
Some have estimated that there were as many as 25,000 kinds of animals represented on the ark. This is a high-end estimation. With two of each kind and seven of some the number of animals would exceed 50,000, though not by very much relatively speaking. Regardless, whether there were 16,000 or 25,000 kinds of animals, even with two of each and seven of some, scholars agree that there was plenty of room for all of the animals on the ark, plus food and water with room to spare.
....With over 1,200 scholarly references to academic studies, Woodmorappe’s book is “a modern systematic evaluation of the alleged difficulties surrounding Noah's Ark” (John Woodmorappe, “A Resource for Answering the Critics of Noah’s Ark,” Impact No. 273 March 1996. Institute for Creation Research, 30 January 2005
http://www.icr.org/pubs/imp/imp-273.htm). Woodmorappe claims that after years of systematically examining all of the questions which have been raised over the years, “all of the arguments against the Ark are… found wanting. In fact, the vast majority of the anti-Ark arguments, at first superficially plausible, turn out to be easily invalidated.”