Diplodocus (CR 12)

Colossal Animal
Alignment: Always neutral
Initiative: +0; Senses: low-light vision, scent, Listen +18, and Spot +19

AC: 14 (-8 size, +12 natural), touch 2, flat-footed 14
Hit Dice: 28d8+273 (399 hp)
Fort +25, Ref +16, Will +10
Speed: 20 ft.
Space: 30 ft./20 ft.
Base Attack +21; Grapple +54
Attack: Tail slap +30
Full Attack: Tail slap +30
Damage: Tail slap 4d8+24
Special Attacks/Actions: Tail sweep, trample 2d8+24
Abilities: Str 44, Dex 10, Con 28, Int 2, Wis 12, Cha 10
Special Qualities:
Feats: Alertness, Improved Natural Attack (tail slap); Run; Toughness (7)
Skills: Listen +18 and Spot +19
Advancement: 29-84 HD (Colossal)
Climate/Terrain: Temperate plains
Organization: Solitary, pair, or herd (6-18)
Treasure/Possessions: None

Source: Dragon #318

Tail Sweep (Ex): As a standard action, a diplodocus can sweep a half- circle with a radius of 40 feet extending from an intersection on the edge of the dinosaur's space. Any creatures smaller than the diplodocus within the swept area are automatically affected. A tail sweep automatically deals 2d8+24 points of damage. Creatures in the area of effect can attempt DC 27 Reflex saves to take half damage. The save DC is Strength-based.

The diplodocus is an herbivore and by nature not a violent creature. Yet they are quick to react to perceived threats, Against smaller targets, a diplodocus uses its tail sweep to send enemies into disarray before taking advantage of the distraction to flee. Larger predators are rare, but when encountered, the diplodocus uses its tail slap and depends on other diplodocuses for protection.