From what I've read, pre-flood people and animals were giant size; there was a greater oxygen level to support their size. For example, fossils of dragonflies with three foot wingspans have been found. That was also the time of the giant trees, which would have produced an incredible amount of oxygen. According to the book of Enoch, before the flood angels cut down the massive trees. The stumps of those trees can be seen all over the world, one of which is Devil's Tower (photo below); the stump is over 800 ft high.

The actual nephilim had six fingers on each hand and six toes on each foot. Latent genes can be seen in some people today (check "celebrities with six toes").

Some research points to the Tartaria era being the millennial reign of Christ (architectural perfection, dates on buildings changed in our era & timeline altered, giant doors indicate size of people during that era).

Much that has been hidden is coming to light now.