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: None

Source: Monster Manual II


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.

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.