Triceratops (CR 9)

Huge Animal
Alignment: Always neutral
Initiative: -1 (Dex); Senses: low-light vision, scent, Listen +13, and Spot +12

AC: 18 (-2 size, -1 Dex, +11 natural), touch 7, flat-footed 18
Hit Dice: 16d8+124 (196 hp)
Fort +19, Ref +9, Will +6
Speed: 30 ft.
Space: 15 ft./10 ft.
Base Attack +12; Grapple +30
Attack: Gore +20 melee
Full Attack: Gore +20 melee
Damage: Gore 2d8+15
Special Attacks/Actions: Powerful charge, trample 2d12+15
Abilities: Str 30, Dex 9, Con 25, Int 1, Wis 12, Cha 7
Special Qualities:
Feats: Alertness; Great Fortitude; Toughness (4)
Skills: Listen +13 and Spot +12
Advancement: 17-32 HD (Huge); 33-48 HD Gargantuan)
Climate/Terrain: Temperate Plains
Organization: Solitary or pair
Treasure/Possessions: None

Source: Monster Manual

Trample (Ex): A triceratops can trample Medium-size or smaller creatures for 2d12+5 points of damage. Opponents who do not make attacks of opportunity against the triceratops can attempt a Reflex save (DC 23) to halve the damage.

These creatures are likely to charge and skewer any creature of at least Large size that infringes on their territory. A triceratops uses its trample attack on smaller opponents.