Stegosaurus (CR 7)

Gargantuan Animal
Alignment: Always neutral
Initiative: -2 (Dex); Senses: low-light vision, scent, Listen +14, and Spot +18

AC: 14 (-2 Dex, -4 size, +10 natural), touch 4, flat-footed 14
Hit Dice: 18d10+183 (264 hp)
Fort +23, Ref +9, Will +8
Speed: 40 ft.
Space: 30 ft. (long)/10 ft.
Base Attack +13; Grapple +33
Attack: Slam +17 melee
Full Attack: 2 slams +17 melee (2d6+8) and tail slap +12 melee (4d6+12)
Damage: Slam 2d6+8, tail slap 4d6+12
Special Attacks/Actions: Powerful charge, trample 2d6+12
Abilities: Str 27, Dex 7, Con 30, Int 1, Wis 14, Cha 10
Special Qualities:
Feats: Alertness; Cleave; Great Fortitude; Power Attack; Run; Skill Focus (Spot); Toughness
Skills: Listen +14 and Spot +18
Advancement: 19-36 HD (Gargantuan), 37-54 HD (Colossal)
Climate/Terrain: Warm plains
Organization: Solitary, pair, or herd (5-8)
Treasure/Possessions: None

Source: Serpent Kingdoms

Powerful Charge (Ex): A stegosaurus typically begins a battle by charging at its opponent. In addition to the normal benefits and hazards of a charge, this tactic allows the creature to make a single slam attack with a +17 attack bonus that deals 4d8+12 points of damage.

Trample (Ex): Reflex DC 27 half. The save DC is Strength-based.

The stegosaurus is by and large a peaceful animal, but it is quick to defend itself from predators and hunters. When threatened, it uses its two front hooves to kick opponents while swinging its mighty tail about, catching its enemies with the vicious spikes.