Mamenchisaurus?
Mamenchisaurus
Hit Dice: 22d8+157 (253 hp)
Initiative: +1
Speed: 30ft (6 squares)
Armor Class: 12 (-8 size, +1 Dex, +9 natural), touch 3, flat-footed 11
Base Attack/Grapple: +16/+42
Attack: Tail slam +18 melee (4d6+15 plus thunderous snap)
Full Attack: Tail slam +18 melee (4d6+15 plus thunderous snap)
Space/Reach: 50ft/40ft
Special Attacks: Thunderous snap, trample 8d8+15
Special Qualities: Low-light vision, scent
Saves: Fort +22, Ref +14, Will +11
Abilities: Str 30, Dex 12, Con 25, Int 1, Wis 14, Cha 10
Skills: Listen +12, Spot +21
Feats: Alertness, Diehard, Endurance, Great Fortitude, Iron Will, Power Attack, Toughness (x2)
Environment: Warm forests, plains and hills
Organization: Solitary, pair or herd (10-24)
Challenge Rating: 10
Treasure: None
Alignment: Always neutral
Advancement: 23-66 HD (Colossal)
Level Advancement: -
This massive quadruped has a long tail, a box-like head attached to a disproportionately long neck, and a wrinkled, elephantine hide.
Although mamenchisaurs are not the longest, heaviest or otherwise record-setting dimensionally of the massive sauropods, they do have the longest necks of their family.
The neck of a mamenchisaurus takes up almost 40 feet of its 70 foot length and is held at a slightly erect angle. Due to the massive pressures needed to pump blood up to its head, multiple heart-like structures are positioned along its neck. Mamenchisaurs are at a significant advantage when it comes to a wide field of vision and a selection of food from the tallest of trees, but their lives are among the shortest of the sauropods (only seventy-five years at a maximum, barring a violent end) due to their fragile hearts.
Combat
Although they are more closely related to camarasaurs and brachiosaurs than diplodocids, they bear the latter’s whip-like tail, complete with its sonic consequences. More often then not, however, they merely trod on any threat to their safety.
Thunderous Snap (Ex): Although they are ponderous, a mamenchisaurus’ whip-like tail can move faster than sound. Any creature struck by a mamenchisaurus’ tail slam must make a Fortitude save (DC 28) or be stunned for 1d4 rounds and deafened for 1d4 minutes. On a successful save, the creature is merely deafened for 1d4 minutes. The save DC is Constitution based.
Trample (Ex): A mamenchisaurus can literally run over any creatures in its way that are of Gargantuan or smaller size. Creatures trampled must make a Reflex save (DC 31 half) or take 8d8+15 damage. The save DC is Strength based.
Perhaps we should get rid of Toughness x2. Since it qualifies for one epic feat... Epic Toughness?