Many creationists have tried to claim that the order of the fossils is due to hydrodynamic sorting, ecological zonation and the ability of an animal to flee from the rising waters or recolonization. Whitcomb and Morris claim that mammals are on top of the geologic column because they were smarter than other animals and were able, therefore, to flee from the rising flood waters more intelligently.1 This, of course is silly as even humans wouldn't be able to flee from the rising waters by running hundreds of miles (say from Houston to New Mexico where there are mountains) in order to avoid a worldwide inundation.
That being said, I think it will be appropriate to illustrate the craziness of this idea by examining a few of the mammals that Whitcomb and Morris say should have been able to flee from the rising flood waters. My favorite is the glyptodont. This heavily armoured, giant 'armadillo-type' animal would have sunk to the bottom. Here is his picture:
http://home.entouch.net/dmd/glyptodont.jpg
[Sarcastic mode on] Obviously one can clearly see that this animal with the heavy bone armour is perfectly adapted to running and swimming at extreme speeds. [sarcastic mode off]
In David Tyler's recolonization model, this animal must swim from Ararat to South America--the only place where he is found. That is a silly idea.
The next speedy critter we need to consider is the giant sloth. They lived only in the New World. Sloths are not known for their speed across the ground. There is no reason to think that the giant sloth was exceptionally rapid either. Here is what he looked like.
http://home.entouch.net/dmd/glyptodont.jpg
Those stubby back legs with the flat feet will not allow him to run very fast. Why isn't he found with the slow moving amphibians?
And once again, within recolonization, this creature, whose living modern representatives get very cold very easily, had to swim the Atlantic to get to the New World, the only place he was found as a fossil. Once again, rather silly.
And last but not least, the Dodo bird, who couldn't fly and was too stupid to figure out that he needed to flee from man. Why is he found only in the uppermost layers of the geologic column?
http://home.entouch.net/dmd/dodo.jpg
It is patently absurd to believe that these animals could have fled from the rising waters and escaped burial. In both the classical flood model and the recolonizatoin model, this animal must have swum to the Pacific islands he lived on. This simply doesn't make sense.
It is really strange to me with all the catastrophism in the 2000 years after the flood, which is what David Tyler suggests is appropriate to account for all the 75,000 feet of sediment above the Ordovician, that there is no single specimen of a living mammalian species found as a fossil in rocks older than the Miocene. How were the mammals able to avoid burial and death by catastrophism which was so great that we would call it a global flood? David must have birds who can't fly, swim to Pacific Islands, Glyptodonts, who can't swim, must somehow make their way across the already formed Atlantic Ocean, and sloths who can't take the cold must swim cold waters to get to the New World.
Creationists who believe such things are burying their head in the sand.
References
1 Whitcomb and Morris, The Genesis Flood, (Grand Rapids: Baker Book House, 1961), p. 273-277.