Level skip:

Press [Up, Down, Left, Up, Down, Right, Select] two times when the title screen fades and the Tyranosaurus Rex opens its jaws revealing the options. Press Start to start the game. Hold Start and press Select during game play to jump to the next level. 

Hint: 

Saving ammunition:
Save the game when you are near three or under dinosaurs, then just run away. This will save ammunition needed for group attacks or Bosses.