According to the achievements on the front of mmo, i count 13 boss achievements in the new raid. Not bad blizzard... not bad.
Pandaria Raid
Dungeons & Raids
Cretaceous Collector (New) Defeat Horridon in Throne of Thunder without killing any Zandalari Dinomancers.
Forgotten Depths (New) Defeat the bosses in the ancient caverns beneath the Throne of Thunder.
Genetically Unmodified Organism (New) Defeat Primordius in Throne of Thunder without any player absorbing a Mutagenic Pool.
Heroic: Council of Elders (New) Defeat the Council of Elders in Throne of Thunder on Heroic difficulty.
Heroic: Dark Animus (New) Defeat the Dark Animus in Throne of Thunder on Heroic difficulty.
Heroic: Durumu the Forgotten (New) Defeat Durumu the Forgotten in Throne of Thunder on Heroic difficulty.
Heroic: Horridon (New) Defeat Horridon in Throne of Thunder on Heroic difficulty.
Heroic: Iron Qon (New) Defeat Iron Qon in Throne of Thunder on Heroic difficulty.
Heroic: Ji-kun (New) Defeat Ji-kun in Throne of Thunder on Heroic difficulty.
Heroic: Jin'rokh tbe Breaker (New) Defeat Jin'rokh the Breaker in Throne of Thunder on Heroic difficulty.
Heroic: Lei Shen (New) Defeat Lei Shen in Throne of Thunder on Heroic difficulty.
Heroic: Megaera (New) Defeat Megaera in Throne of Thunder on Heroic difficulty.
Heroic: Primordius (New) Defeat Primordius in Throne of Thunder on Heroic difficulty.
Heroic: Ra-den (New) Defeat Ra-den in Throne of Thunder.
Heroic: Tortos (New) Defeat Tortos in Throne of Thunder on Heroic difficulty.
Heroic: Twin Consorts (New) Defeat the Twin Consorts in Throne of Thunder on Heroic difficulty.
Last Stand of the Zandalari (New) Defeat the bosses occupying the ruins at the entrance to the Throne of Thunder.
Praise the Sun! (New) Defeat Nalak, the Storm Lord, in the Lightning Isle.