What about an Arsinotherium or Uintatherium-based dinopriminal?
Spawn of the Elder Darkness
Out of the prime they came, the slayers of suns, the gnawers at the heart of the island universes, them who stop thought. Swiftly they passed through our spheres, and well it was, for else all life upon fair Tellura would have been snuffed out as a candle quenched in the deepest ocean. Yet certain seeds they left behind them, and in the course of ages foul life arose and strove with the clean life native to our orb; and a veil as of mist and darkness was cast across all. Of the wars across the face of the young world no lore of mortals tells, nor do the ageless gods know aught of them, for they were ended aeons before the first of all gods was born. But in the lore of dragons many things remain that are forgotten even by the deathless, and it was there, in the prismed citadels into which I alone of mortals have dared to walk, that I discovered the legends of primaeval night which now I set forth. -- The Draconic 'Primeval Legends', edited and redacted from Elenae Moonowl's The Mastery of Primaeval Night.
They were things that came out of the voids beyond all voids and descended into the primeval slime of the world before the first dinosaurs were born. They established cities that were vast as nations, twisted into geometrical forms impossible under sane conceptions of dimension. Horrible to the point that thinking life died around them, they dwelt beneath a mist-dimmed sun, shaded from the earth by mosses hundreds of feet high and tremendous fungi. In time though, they were beaten back by the advance of the dinosaurs and slain by their intelligent descendants, the mighty dragons.
Once only did the chromatic and the metallic dragons ally, and that was in the great assault on the Cities of the Elder Night. With acid and lightning the dragons blasted the hideous, tainted fungous forests, and with fire and frost they burned away the all-enshrouding mists, laying the cities open to the burning sun. But the fiends of the elder world were too steeped in magical skill to thus be slain forever. Their bodies were destroyed by the sunlight and dragonfire; their spirits nonetheless remained, though hurled screaming into inner earth, from which they at times arise to possess the descendants of their slayers.
Darkness-Ridden Creature (Template)
A darkness-ridden creature is one possessed by the disembodied, tormented spirit of a spawn of elder darkness. They are tortured and gaunt in appearance, and the discolorations and scars on their scaly hides are eerily suggestive of forbidden and ancient sigils.
Creating a Darkness-Ridden Creature
'Darkness-ridden' is an acquired template that can be applied to any dinosaur, any creature of the dragon type, or any creature with the (Reptilian) subtype, though creatures with high Will save bonuses can rarely be possessed.
Size/Type: As base creature, except that animals become magical beasts (augmented animal). Do not recalculate HD, base attack bonus, saves, or skills.
Hit Dice: As base creature
Speed: A darkness-ridden is driven on by unnatural forces, pushing the body to its limits. Its speed increases by 10 ft. for all movement types.
Armor Class: A darkness-ridden is enshrouded by disturbing distortions, as geometry around it twists in seemingly impossible ways. This throws off attackers' fighting form, giving the darkness-ridden a +2 circumstance bonus to Armor Class.
Attacks: A darkness-ridden retains the attacks of the base creature. In addition, it gains entropic touch, a melee touch attack dealing 1d8 damage per 3 full Hit Dice (creatures with 2 or fewer Hit Dice deal 1d4 damage). This damage is untyped damage and cannot be reduced by any form of damage reduction, resistance, or immunity.
Special Attacks: A darkness-ridden retains the base creature's special attacks and gains the following:
Entropic Touch (Su): A darkness-ridden has a touch attack that infuses victims with harmful, life-decaying energies (see Attacks). In addition, a darkness-ridden with at least 5 HD deals 1d2 points of Strength damage when it makes a successful touch attack with its entropic touch. Every 5 HD thereafter the Strength damage increases (to 1d3, then 1d4, 1d6, 1d8, 2d6, 2d8, 3d6, etc.)
Minddeath Burst (Su): A darkness-ridden with at least 10 HD can, three times per day, emit a flash of mindshredding horror. All creatures with an Intelligence score within 5 ft / HD suffer 1d6 Intelligence drain (Will DC 10 + 1/2 darkness-ridden's HD + darkness-ridden's Cha modifier negates).
Special Qualities: A darkness-ridden retains the base creature's special qualities and gains the following:
Damage Reduction (Su): A darkness-ridden with at least 10 HD gains DR 10/magic. One with 20 HD or more improves this to DR 10/epic.
Light Susceptibility (Ex): A darkness-ridden is dazzled in full daylight or equivalent lighting (such as the effect of a daylight spell).
Mindwarping Aura (Su): A darkness-ridden with at least 5 HD emits an aura that disrupts thought. All creatures with an Intelligence score within 10 ft / 2 full HD must make a Will save (DC 10 + 1/2 darkness-ridden's HD + darkness-ridden's Cha modifier + 2 from Ability Focus bonus feat) or take 1d3 points of Intelligence damage. If they remain within the aura, this save must be repeated once per hour.
Protected Mind (Su): A darkness-ridden is immune to Charisma, Intelligence, and Wisdom damage or drain.
Profane Secrets (Su): A darkness-ridden gains a +1 profane bonus to attack rolls and skill checks, plus +1 per 10 full HD.
Spell Resistance (Su): A darkness-ridden with 10 HD or more gains SR of 10 + 1/2 its HD.
Abilities: Con +2, Int increased to 10 if not already higher (otherwise unchanged), Wis +4, Cha +4
Skills: Recalculate skill points if Intelligence is increased. A darkness-ridden gains a +4 competence bonus to Knowledge (arcana) checks.
Feats: A darkness-ridden gains Ability Focus (Mindwarping Aura) as a bonus feat. In addition, it gains Iron Will as a bonus feat if it does not already possess that feat.
Organization: Solitary
Challenge Rating: If the base creature's CR is less than 1, then the base creature's CR is doubled (if this results in CR 2/3, round up to 1). Otherwise:
<9 HD: CR +1
10+ HD: CR +2
Alignment: Always chaotic evil
Example: Darkness-Ridden Megaraptor
Size/Type: Large Magical Beast (Augmented Animal)
Hit Dice: 8d8+51 (87 hp)
Initiative: +2
Speed: 70 ft. (14 squares)
Armor Class: 19 (-1 size, +2 Dex, +6 natural, +2 profane), touch 13, flat-footed 17
Base Attack/Grapple: +6/+15
Attack: Talons +11 melee (2d6+5); or entropic touch +11 melee (4d6 and 1d2 Str damage)
Full Attack: Talons +11 melee (2d6+5) and 2 foreclaws +6 melee (1d4+2) and bite +6 melee (1d8+2); or entropic touch +11 melee (4d6 and 1d2 Str damage)
Space/Reach: 10 ft./5 ft.
Special Attacks: Entropic touch, pounce
Special Qualities: Light susceptibility, low-light vision, mindwarping aura, profane secrets, protected mind, scent
Saves: Fort +11, Ref +8, Will +8
Abilities: Str 21, Dex 15, Con 23, Int 10, Wis 19, Cha 14
Skills: Hide +9, Jump +27, Knowledge (arcana) +15, Listen +12, Spot +12, Survival +12
Feats: Ability Focus (mindwarping aura) (B), Iron Will (B), Run, Toughness, Track
Environment: Warm forests
Organization: Solitary
Challenge Rating: 7
Treasure: None
Alignment: Always chaotic evil
Advancement: 9-16 HD (Large); 17-24 HD (Huge)
Level Adjustment: -
This creature is an emaciated, tormented giant raptor, with dark agony and malice burning in its eyes. Its scales have begun to turn gray in patterns which hint at certain age-old and dreadful runes.
Entropic Touch (Su): The darkness-ridden megaraptor's entropic touch deals 4d6 damage and 1d2 Strength damage.
Mindwarping Aura (Su): The darkness-ridden megaraptor emits an aura that disrupts thought. All creatures with an Intelligence score within 40 feet must make a Will save (DC 18) or take 1d3 points of Intelligence damage. If they remain within the aura, this save must be repeated once per hour.
Profane Secrets (Su): The darkness-ridden megaraptor gains a +1 profane bonus to attack rolls and skill checks.