Cryptoclidus (CR 3)

Large Animal (Aquatic)
Alignment: Always neutral
Initiative: +3 (Dex); Senses: darkvision 60 ft., low-light vision, scent, Listen +5, and Spot +5

AC: 16 (-1 size, +3 Dex. +4 natural), touch 12, flat-footed 13
Hit Dice: 3d8+9 (22 hp)
Fort +6, Ref +6, Will +2
Speed: Swim 60 ft.
Space: 10 ft./5 ft.
Base Attack +2; Grapple +10
Attack: Bite +5 melee
Full Attack: Bite +5 melee
Damage: Bite 1d8+6
Special Attacks/Actions: Swallow whole
Abilities: Str 18, Dex 16, Con 17, Int 2, Wis 13, Cha 9
Special Qualities:
Feats: Alertness; Dodge
Skills: Hide +1, Listen +5, Spot +5, and Swim +12
Advancement: 4-6 HD (Large); 7-9 HD (Huge)
Climate/Terrain: Warm aquatic
Organization: Solitary or school (20-40)
Treasure/Possessions: None

Source: Monster Manual II

Improved Grab (Ex): If cryptoclidus hits an opponent that is at least one size category smaller than itself with a bite attack, it deals normal damage and attempts to grapple as a free action without provoking an attack of opportunity (grapple bonus +10). If it gets a hold, it can try to swallow the opponent. Alternatively, the cryptoclidus the option to conduct the grapple normally, or simply use its jaws to hold the opponent (-20 penalty on grapple check but cryptoclidus is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals bite damage.

Swallow Whole (Ex): Cryptoclidus can swallow a grabbed opponent that is at least two size categories smaller that by making a successful grapple check (grapple bonus +10.) Once inside the gullet, the opponent takes 1d8+4 points bludgeoning damage plus 1d6+2 points of acid damage per round from the dinosaur's digestive juices. A successful grapple check allows the swallowed creature to climb out 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 Large cryptoclidus's gullet can hold 1 Small, 4 Tiny, or 16 Diminutive or smaller opponents.

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

Cryptoclidus normally hunts fish, darting its neck into traveling schools and snapping up prey with its sharp teeth. However, it is capable of traveling on the surface of the water and occasionally seeks larger prey.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.