Tyrannosaurus, Cave (CR 5)

Large Animal
Alignment: Always neutral
Initiative: +2 (Dex); Senses: darkvision 60 ft., scent, Listen +8, and Spot +8

AC: 15 (-1 size, +2 Dex, +4 natural), touch 11, flat-footed 13
Hit Dice: 9d8+30 (70 hp)
Fort +9, Ref +8, Will +5
Speed: 40 ft.
Space: 10 ft./10 ft.
Base Attack +6; Grapple +17
Attack: Bite +12 melee
Full Attack: Bite +12
Damage: Bite 2d6+10
Special Attacks/Actions: Improved grab, swallow whole
Abilities: Str 25, Dex 14, Con 17, Int 2, Wis 15, Cha 10
Special Qualities:
Feats: Alertness; Improved Natural Attack (bite); Toughness; Track
Skills: Listen +8, Spot +8, and Survival +6
Advancement: 10-14 HD (Large); 15-27 HD (Huge)
Climate/Terrain: Underground
Organization: Solitary, pair, pack (3-8 plus 50% chance for 1 leader with 14 HD)
Treasure/Possessions: None

Source: Miniatures Handbook

Improved Grab (Ex): To use this ability, a cave tyrannosaurus must hit an opponent of up to one size smaller with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can try to swallow the foe in the following round.

Swallow Whole (Ex): A cave tyrannosaurus can try to swallow a grabbed opponent of up to two sizes smaller by making a successful grapple check. A swallowed creature takes 2d6+7 points of bludgeoning damage and 6 points of acid damage per round from the cave tyrannosaurus's gizzard. A swallowed creature can cut its way out by using a light slashing or piercing weapon to deal 20 points of damage to the gizzard (AC 12). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out.

A cave tyrannosaurus's gizzard can hold 2 Small, 8 Tiny or 32 Diminutive or smaller opponents.

A hunter pure and simple, a cave tyrannosaurus is likely to attack Small creatures and retreat once it has secured a meal.