Something that intrigues people who think about the pre-flood world is, what would it have looked like? Besides the climate considerations, which tend to be the focus of the conversation when the pre-fall world comes up, there is the question of what did the pre-fall organisms look like? While there is no definitive way know, examining genetics and fossils can provide us with some clues about what pre-flood diversity looked like.
The important thing to understand is that the flood was a massive extinction event. Thousands of what we call “species” would have gone extinct in the rushing floodwaters. Some whole kinds of plants, insects and water organisms would also have gone extinct in the massive underwater sediment flows that accompanied the flood. This may partially explain the massive ferns, fish and insects that are fossilized in the rock record. However, genetically, the impact may have been much larger.
Genetically, the flood wiped the population of most organisms down to very low levels. As a result, genetic diversity was lost. However, the amount lost was not equal for all organisms. Some plants would have lost a ton of diversity, to the point of extinction. Others would have more easily recovered and retained their diversity. I suspect the orchid family with its myriad of forms would be an example of one that lost very little diversity in the flood. On the other hand, ferns appear to have suffered heavily during the flood, as many of the giant ferns found in the fossil record disappear after the flood. The same could be said of insects and of sea creatures.
However, what everyone wants to know about are the land animals on the Ark. Does what we observe in the present in any way resemble the pre-flood world? My suspicion is that what we observe today is similar to what existed in the pre-flood world. However, this would depend strongly on whether the kind was clean or unclean. The clean kindsa and flying creatures had more animals on the Ark than the unclean kinds (seven or fourteen depending on who you talk to). This increased number would have guaranteed a wider range of genetic diversity in the post-fall world as there would have been more varieties of genes available due to the larger number of individuals. A good example of this is the sheep-goat kind which in the post-flood world looks very different.
Members of the kinds which only had two representatives on the Ark would potentially have a lower level of genetic diversity in the post-flood world. However, this is not a guarantee. The dog kind is not one of the clean kinds, yet it is perhaps one of the most widely diversified of all kinds. There could be a number of reasons for this. It could be that much of the dog diversity is mutation-driven (which it is) and that the dog genome is just more resistant to mutation damage than some other kinds. Another option is that the dog genome that entered the Ark contained all the genetic diversity that ever existed in the dog genome, enabling them to repopulate in the same manner as the pre-flood dogs.
The two options for dogs are not mutually exclusive, nor are they limited to only kinds which had a mere two representatives on the Ark. It is certainly possible that a kind on the Ark could have represented all the genetic diversity that existed in the pre-flood world, as well as being able to handle a heavier mutation load. However, it is equally possible that the animals God brought to the Ark did not represent the sum of the pre-flood genetic diversity. It is possible certain designs in their post-fall world would have been too dangerous or too pestilent to man in the post-flood world and God thus ensured that these genes did not survive the flood.
Exactly what pre-flood animals and plants looked like is unknown entirely. The fossil record gives us a few clues about possible combinations but really, there is no way to know for certain. What we can know from the fossil record is that everything we find can be fitted into a specific kind. We find no undisputed transitional forms in the fossil record, proving once again that the Bible is right about the creation of the universe.