Everyone's favorite. I'm pretty sure this one will be in the Pathfinder bestiary; I made this conversion so that I would have it handy for this weekend's game.
TYRANNOSAURUS
CR 8 (4,800 XP)
N HUGE ANIMAL
Init +1; Senses Low-light vision, scent; Perception +13
DEFENSE
AC 15; touch 9, flat-footed 16 (+1 Dex, -2 size, +8 natural)
hp 188 (18d8+107)
Fort +16, Ref +12, Will +8
OFFENSE
Speed 40 ft.
Melee Bite +20 (3d6+13)
Space 15 ft.; Reach 10 ft.
Special Attacks: Grab, swallow whole
STATISTICS
Str 28, Dex 12, Con 21, Int 2, Wis 15, Cha 10
Base Atk +13; CMB +30; CMD 41
Feats: Alertness, Improved Great Fortitude, Improved Initiative, Improved Natural Armor (x3), Improved Natural Attack (bite), Run, Toughness
Skills: Perception +13, Stealth +5; Racial Modifiers Perception +2
Languages: none
ECOLOGY
Environment: Warm forests and plains
Organization: Solitary or pair
Treasure: None
SPECIAL ABILITIES
Grab (Ex): If a tyrannosaurus hits with its bite attack, it deals damage as normal and attempts to start a graple as a free action without provoking an attack of opportunity. If the tyrannosaur gets a hold, it can attempt to swallow its prey whole.
Swallow Whole (Ex): A tyrannosaurus can try to swallow a grabbed opponent of up to two sizes smaller by making a successful grapple check. The swallowed creature takes 2d8+8 points of bludgeoning damage and 8 points of acid damage per round from the tyrannosaurus’s gizzard. A swallowed creature can cut its way out by using a light slashing or piercing weapon to deal 25 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 Huge tyrannosaurus’s gizzard can hold 2 Medium, 8 Small, 32 Tiny, or 128 Diminutive or smaller opponents.
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Despite its enormous size and 6-ton weight, a tyrannosaurus is a swift runner. Its head is nearly 6 feet long, and its teeth are from 3 to 6 inches in length. It is slightly more than 30 feet long from nose to tail.
A tyrannosaurus pursues and eats just about anything it sees. Its tactics are simple—charge in and bite.