Tyrannosaurus (CR 8)

Huge Animal
Alignment: Always neutral
Initiative: +1 (Dex); Senses: low-light vision, scent, Listen +14, and Spot +14

AC: 14 (-2 size, +1 Dex, +5 natural), touch 9, flat-footed 13
Hit Dice: 18d8+99 (180 hp)
Fort +16, Ref +12, Will +8
Speed: 40 ft.
Space: 15 ft./10 ft.
Base Attack +13; Grapple +30
Attack: Bite +20 melee
Full Attack: Bite +20 melee
Damage: Bite 3d6+13
Special Attacks/Actions: Improved Grab, shallow whole
Abilities: Str 28, Dex 12, Con 21, Int 2, Wis 15, Cha 10
Special Qualities:
Feats: Alertness; Improved Natural Attack (bite); Run; Toughness (3); Track
Skills: Hide -2, Listen +14, and Spot +14
Advancement: 19-36 HD (Huge); 37-54 HD Gargantuan)
Climate/Terrain: Warm Plains
Organization: Solitary or pair
Treasure/Possessions: None

Source: Monster Manual

Improved Grab (Ex): To use this ability, the tyrannosaur must hit a Medium-size or smaller opponent with its bite attack. If it gets a hold, it can try to swallow the foe.

Swallow Whole (Ex): A tyrannosaurus can try to swallow a Medium-size or smaller opponent by making a successful grapple check. The swallowed creature takes 2d8+8 points of crushing damage per round plus 8 points of acid damage from the tyrannosaurus's gizzard. A swallowed creature can cut its way out by using claws or a Small or Tiny slashing weapon to deal 25 points of damage to the gizzard (AC 20). Once the creature exits, muscular action closes the hole; another swallowed opponent must again cut its own way out.

The tyrannosaurus's gizzard can hold two Medium-size, four Small, eight Tiny, sixteen Diminutive, or thirty-two Fine or smaller opponents.

A tyrannosaurus pursues and eats just about anything it sees. Its tactics are simple - charge in and bite.