Archelon (CR 8)

Huge Animal
Alignment: Always neutral
Initiative: -2 (Dex); Senses: low-light vision, Listen +11, and Spot +6

AC: 21 (-2 size, -2 Dex, +15 natural), touch 6, flat-footed 21
Hit Dice: 12d8+84 (138 hp)
Fort +16, Ref +2, Will +5
Speed: 10 ft., swim 20 ft.
Space: 15 ft./10 ft.
Base Attack +9; Grapple +26
Attack: Bite +16 melee
Full Attack: Bite +16 melee
Damage: Bite 2d6+13
Special Attacks/Actions: -
Abilities: Str 28, Dex 7, Con 22, Int 2, Wis 13, Cha 7
Special Qualities: Hold breath
Feats: Great Fortitude; Toughness (x4)
Skills: Listen +11, Spot +6, and Swim +17
Advancement: 13-24 HD (Huge); 25-36 HD (Gargantuan)
Climate/Terrain: Warm aquatic
Organization: Solitary or pair
Treasure/Possessions: None

Source: Stormwrack

Hold Breath (Ex): An archelon can hold its breath for a number of rounds equal to 10 x its Constitution score before it risks drowning. For a typical archelon, this is 220 rounds, or 22 minutes.

Skills: An archelon has a +8 racial bonus on any Swim check to perform a special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

The archelon attacks with a snap of its over-sized jaws.