#scythid

The original Scythids came in several varieties, but lacked elemental dispositions. They were, from the smallest to the greatest, the dog-like sprinters and runners, which preferred to ram and gore targets, often tipping over vehicles; semi-serpentine Reavers, which tended to attack from cliffsides and use tusk and blade-like arm appendages to maul prey; the huge and mammoth-like Ravagers, which burst from the ground and attempted to grieve or pince opponents with their massive, scythe-like tusks; and the gargantuan and fearsome Ruiners, which were much to the effect of a Ravager, but thrice its size, four-tusked, and capable of vomiting caustic bile as well as performing a fierce, area-effect ground slam. In the end, Gearbox discarded these beautific beasts in favor of slugs, claiming they were "too much like Zerg" in both form and function.

So, Sprinters are Sprinters (official screenshot of Brown period):

Ruiners are probably Warriors (I have doubts), both can jump very high. 

Another creature on Pandora, that have same mouthparts is Crab Worm:

I guess Crab Worm could be a Scythid Reaver?

Ravager’s description reminds of Rakk Hive, and their jaws look familiar (another Brown period promo screenshot)

One way or another this Scythid family concept was declained.

Another thing necromorph-slayinglovemachine mentioned is giant skulls and bones all over Pandora. I always thought that they must belong to some whale or Megalodon like creatures. One of skulls’ model (the one wich obviously of Scythid family) is named Syth Skull:

The skeleton added in Secret Armory really belongs to fish, it used in BL2 scenery a lot:

I don’t have ideas about this one, it can’t be Scythid family since it have eyeholes (and I don’t remember were these skulls even big):

Probably Bullymongs have similiar skull but they also have Scythid’s mandibles/jaws without cheliceraes (like fish above).