Combining mobile autorunner and tower defense gameplay styles with Noah's ark and trains is such a cool and very unique idea! Great job! :)
(If you continue developing this idea, you could give each animal different attack types. Plus, if you combine two of the same animal on one train car, they could get boosted stats, thus serving as a reference to God's command to fill the ark with two of each animal. You don't have to use these ideas of course, but I just wanted to share some thoughts I had...)