Quadruped

Cost: [-35]

Quadruped is an Organism Meta-Trait.

• Quadruped [-35]: Extra Legs (Four Legs) [5]; Horizontal [-10]; and No Fine Manipulators [-30]

Quadruped Explanation

At first glance the Extra Legs (Four Legs) part of the Meta-Trait doesn't make sense but it all has to do with how GURPS defines legs and arms.

• "In GURPS, a limb with which you can manipulate objects is an arm, regardless of where it grows or what it looks like." An unusually dextrous leg that can manipulate objects is considered a Leg with the Foot Manipulator disadvantage ([-3] up to two legs) or limitation (-30% when appplied to extra legs)
• "If you can walk on a limb but cannot use it to manipulate objects, it is a leg in GURPS. [...] The human norm is two legs, which costs 0 points. It costs points to have more than two legs"
• "Example: You can use your feet as hands, but can’t walk while doing so. This is Extra Arms 2 (20 points) with Temporary Disadvantage: Legless (-30%), for 14 points."

Per this Horizontal and No Fine Manipulators alone would result in two limbs that could not function as legs ie they don't support your weight, they are effectively Paraplegic, or something else that prevents them from being used as legs in the manner GURPS defines them.

Hence the need for Extra Legs - it's not really extra legs in terms of the number of limbs but rather allows two of your limbs to function as legs.