You may be confused by the Pathfinder.
At first glance, he doesn't look like much, armed only with a shotgun, a pack of flares and a machette. He's a support class, just meant to blind dinosaurs and put in a couple shots here and there, right? Wrong.
In this guide I will attempt to prepare you to play the Pathfinder using a few tricks and facts I've discovered recently. If you've been playing every class except him, this is the guide for you.

Now, I know what you're thinking. Why would anyone want to use a glorified sparkler when he could be netting his foes or, better yet, blowing them up? Well, if you've ever played on the dinosaur team, you will probably have noticed those glaring pink beacons that obscure everything inside them. Those are deployed flares. For some reason, humans don't so much as squint at them, but dinosaurs looking at them get a taste of their own dilophosaur spit.
For this reason, a Pathfinder is a valuable asset to the mercenary team. A well-placed flare can mean the difference between making it to the ammo crate and getting squashed by a T-Rex.
Quick Tips:

• Conserve your flares. They're best used when a large portion of your team is clumped together in an easily-defensible location, and best used against Tyrannosaurs and raptors.
  
• Throw carefully. If you're moving towards a stationary group of allies, you can throw your flare directly ahead; it should land in the middle of the group. If you're already part of that group, throwing the flare straight up keeps it from landing too far away.
  
• Sometimes it's better to throw than to shoot. If a T-Rex is bearing down on you, consider using a flare before you start shooting. If you've been caught unawares by a raptor, try to blind it if you can get it out of your face.

When I first started playing PC, I too was underwhelmed by the Pathfinder. His shotgun just didn't seem to cut it. Apparently I wasn't doing something right, though, because now I derive great pleasure from giving raptors mothfuls of buckshot.
As in other games, the shotgun is a close-range weapon. It'll take some practice to learn what the effective range is, but you can rest assured that most Pteranodons will be out of reach, even if they seem to be flying low. If you see one diving for a teammate, however, open fire.
The shotgun is also great for finishing off fleeing foes. An escaping Carnotaurus or Novaraptor is only safe once it's gotten into the long-range area. If it's in medium range (again, figuring out the shotgun's range will take practice), try to nail it with a direct hit. It's more than likely that your teammates have weakened it enough to land you the kill.
One of the more risky (but more rewarding) ways to use the shotgun is T-Rex kiting. If a T-Rex tries to eat you, you can often sidestep the initial lunge and begin running in circles around the dinosaur faster than he can turn. A crucial part of this technique is jumping; without it, you won't get away from the Rex's feet or maw fast enough to kill it. If you have at least six shots, a bit of skill and a bit of luck, you should be able to down the titan with rage-inducing ease.
Recap:

• Don't shoot Pteranodons unless they're really close. It's always good to take pock shots until you learn your weapon's range, though!
  
• If a dinosaur is fleeing, it's likely wounded enough for you to kill it in one or two shots, even at medium range.
  
• It is possible to single-handedly take down a T-Rex by running and jumping around it while shooting.

While the Pathfinder may seem a weak support class to the inexperienced, when correctly played he is a force to be reckoned with. Raptors that try to claw you instead of tackling you will find their skulls knocked in by an entire shot, and Tyrannosaurs everywhere will learn to fear the sound of your weapon cocking. Even if you're not that great as a Pathfinder, you'll still give your enemies headaches with your strategically-placed flares... literally. Thank you for reading. I hope (and to some degree expect) that I've convinced and helped you to use what is currently a bit of an underused class.