Spinosaurus (CR 13)

Gargantuan Animal
Alignment: Always neutral
Initiative: +1 (Dex); Senses: darkvision 60 ft., low-light vision, scent, Listen +16, and Spot +15

AC: 16 (-4 size, +1 Dex, +9 natural), touch 7, flat-footed 15
Hit Dice: 20d8+132 (222 hp)
Fort +18, Ref +13, Will +8
Speed: 40 ft.
Space: 20 ft./20 ft.
Base Attack +15; Grapple +23
Attack: Bite +24 melee and 2 claws +19 melee
Full Attack: Bite +24 melee and 2 claws +19 melee
Damage: Bite 2d8+13, claw 2d6+6
Special Attacks/Actions: Frightful presence, improved grab, swallow whole, trample 2d8+19
Abilities: Str 36, Dex 13, Con 23, Int 2, Wis 15, Cha 10
Special Qualities:
Feats: Alertness; Run; Toughness x4; Track
Skills: Listen +16 and Spot +15
Advancement: 21-40 HD (Gargantuan); 41-60 HD (Colossal)
Climate/Terrain: Warm forests, plains, hills, and marsh
Organization: Solitary or pair
Treasure/Possessions: None

Source: Monster Manual II

Frightful Presence (Ex): When a spinosaurus bellows (a standard action), it inspires terror in all creatures within 30 feet that have fewer Hit Dice or levels than it has. Each potentially affected opponent must succeed at a Will save (DC 20) or become shaken for 5d6 rounds. A successful save leaves that opponent immune to that spinosaurus's frightful presence for 24 hours.

Improved Grab (Ex): If spinosaurus hits an opponent that is at least one size category smaller than itself with a bite attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +40). If it gets a hold, it can try to swallow the opponent in the next round. Alternatively, spinosaurus has the option to conduct the grapple normally, or simply use its jaws to hold the opponent (-20 penalty on grapple check, but spinosaurus is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals bite damage.

p>Swallow Whole (Ex): Spinosaurus can swallow a grabbed opponent that is at least two size categories smaller than itself by making a successful grapple check (grapple bonus +40). Once inside the gullet, the opponent takes 2d8+10 points of bludgeoning damage plus 1d8+4 points of acid damage per round from the dinosaur's digestive juices. A successful grapple check allows the swallowed creature to climb out of the gullet and return to the mouth, where another successful grapple check is needed to get free. Alternatively, a swallowed creature can try to cut its way out with either claws or a light piercing or slashing weapon. Dealing at least 25 points of damage to the digestive tract (AC 20) in this way creates an opening large enough to permit escape. Once a single swallowed creature exits, muscular action closes the hole; thus, another swallowed opponent must cut its own way out. A Gargantuan spinosaurus's gullet can hold 2 Large, 8 Medium-size, 32 Small, or 128 Tiny or smaller opponents.

Trample (Ex): As a standard action during its turn each round, spinosaurus can trample opponents at least one size category smaller than itself. This attack deals 2d8+19 points of bludgeoning damage. A trampled opponent can attempt either an attack of opportunity at a 4 penalty or a Reflex save (DC 33) for half damage.

Skills: Spinosaurus receives a +2 racial bonus or Listen and Spot checks.

Scent (Ex): A dinosaur can detect approaching enemies, sniff out hidden foes, and track by sense of smell.

Though capable of running down prey, spinosaurus prefers to freeze opponents in their places with an unearthly, soul-searing bellow. When it must chase prey, it tramples smaller creatures and grabs larger ones with its powerful jaws while tearing with its claws.