I found it. It was none other than the Fenris Wolf:
Augmented Critical (Ex): The Fenris wolf's bite threatens a critical hit on a natural attack roll of 18–20, dealing triple damage on a successful critical hit. Additionally, the victim must succeed on a DC 76 Fortitude save or lose a hand or foot (Fenris wolf's choice) A victim who loses a foot falls prone and has its land speed reduced to 5 feet. A severed hand make it impossible for the subject to use objects or cast spells with somatic components. The save DC is Strength-based.