It was a ...really ...big ...boat which had a capacity of a train with over 500 railroad containers.
Have you ever seen a really long train and counted its cars as it went by?
I remember a train once that stretched into the distance to where I couldn't see where it ended. I decided to count the cars as it went by and it was just barely over 100 cars and took several minutes.
For comparison sake the longest train recorded was in Australia having 682 cars and was 7.353 km long.
If we cross multiply proportionately, the capacity of Noah's Ark likened to a train with 522 cars would be 5.627 km long.
Or 3.5 miles...Have you ever walked 3.5 miles in a straight line?
If so you'd know it would take you about an hour at the average human walking speed.
Combine all that into a ship.
In 1993, research was carried out by naval architects and structural engineers at the world class KRISO ship research facility in Korea, testing the proportions described in Genesis - 300 x 50 x 30 cubits. They concluded that the proportions were near optimal and that the scale was feasible in waves up to 30m.
Also notice that while we use to, we now don't have Dinosaurs or 40 foot long Crocs anymore...perhaps the big scary animals got left behind during the flood.
Consider the Oxygen content of the atmosphere also must have changed since the water in the firmament fell to earth. A higher content of Oxygen in the atmosphere plays a role in animal growth size. Before the flood this concentration may have been as high as 40% compared to our 20% now.
In order for fossils to be encased in sedimentary rock there's got to be a lot of sediment falling on top of them like snow in a blizzard.
Then again Perhaps some of the animals got eaten for food when God gave the go ahead to eat all animals.
Genesis 9
1Then God blessed Noah and his sons, saying to them, “Be fruitful and increase in number and fill the earth. 2The fear and dread of you will fall on all the beasts of the earth, and on all the birds in the sky, on every creature that moves along the ground, and on all the fish in the sea; they are given into your hands.
3 Everything that lives and moves about will be food for you. Just as I gave you the green plants, I now give you everything.
We still have turtles which get up to 2000 pounds though.
There's many factors to be taken into consideration. All of these factors must be utilized in order to arrive at an accurate conclusion.
But we do know if God created the animals he also knew what he was doing when he designed the Ark.