Jack, an aptly named 17 pound Jack Russell terrier more accustomed to chasing squirrels, treed a mountain lion near the family farm in Colman South Dakota. The Argus Leader  has a write up about Jack, Virtus and Chad Strenge and a day they probably won't forget anytime soon.
[Jack] chases squirrels around their Colman farm every day, but he made such a fuss Tuesday morning that Virtus, Chad's father, had to step out of the shop to investigate. They could hardly believe what Jack had found. "He comes running back in saying, 'Get the gun, there's a mountain lion out there,' " Chad Strenge said. "I said, 'Yeah, right.'"
He grabbed the closest gun he could find - a 12-gauge shotgun - and took it outside. Sure enough, there he was: a full-grown, 150-pound mountain lion, up a tree and staring down at the barking terrier.