In the Pokémon Adventures manga, the statue in Eterna City is neither Dialga or Palkia but a combination of the two statues. Pearl and Diamond theorize that long ago, the people saw Dialga and Palkia fighting each other resulting time and space being warped, making them look like a single entity.
This is a reflection of the statue's appearance in Pokémon Diamond and Pearl and Pokémon Platinum being ambiguously shaped in order to represent a different member of the duo in each game. In Pokémon Brilliant Diamond and Pokémon Shining Pearl, updated graphics made the statue look exactly as how it did in Pokémon Adventures.