Dino dex

Refactored code and cleaned up arrowheads following discussion with Dan
`2000` is a magic number here. define it as a constant instead, and use that constant. that way if the definition of a "big" dino ever changes (ie, if the threshold goes from 2000 to 3000), you can just change the constant definition, instead of having to replace the hardcoded number here and on line 15.