What is Lugia?
Lugia is a very interesting Pokémon. Unlike most legendary Pokémon, at first glance it doesn't appear to be based on anything specific.
Please click here to see one of Lugia's official biography pages.
Many people often argue that it could be a bird, a dragon, a whale or a mixture of many things. My personal opinion is that Lugia is most like an early bird or a dinosaur. Let me explain why.
I fail to see any dragon-like traits in Lugia at all. Despite the long neck, fins on its back and huge wings, I think all of these traits are FAR more akin to that of dinosaurs.
The only other animal that had a double line of plates along the back like Lugia's fins was the Stegosaurus (and other dinosaurs from this family), notice they also have spikes on their tails. People regularly forget this major shared trait.
The shape of Lugia's head and beak are very similar to various dinosaurs and not dragons. Going by the standards, dragons have six limbs, claws, snouts etc. whereas many dinosaurs had head crests of all shapes and sizes.
People appear to have forgotten about dinosaurs when looking for something to compare Lugia against, so dragons may be the next nearest option for some.
Lugia is presumed to be feathered (the Silverwing is supposedly a feather from a Lugia and in Pokémon XD: Gale of Darkness it can learn Feather Dance after purification). Feathers are very much a bird or early-bird trait.
"Wait a second! Doesn't Lugia use Dragon type moves too!?"
Yes, but actually every Dragon type move that Lugia can learn either by leveling up or by TM is NOT exclusive to Dragon Pokémon (in terms of type and biology). Yveltal and Dragon Rush are a good and recent example of this, a useful bit of info to counter the discussions about Lugia possibly using Dragon Rush in Pokémon Movie 18.
Now if we go back to the move Feather Dance, currently it is strictly ONLY learned by feathered Pokémon such as Starly. Often people question whether Lugia really does have feathers based on his smoothness and shininess. As we can see from the previous image, water-dwelling birds have evolved very specialised feathers which give the appearance of smooth skin.
The odd thing about Lugia's cry is that in the games it sounds a stereotypical dinosaur roar, but in the anime it sounds much more like a whale (in fact humpbacked whale calls were used to create Lugia's call).
So perhaps Lugia has a bit of cetacean in there too. This may explain its five-digit wings (a cetacean skeleton trait).
Lugia's feet are unlike that of either birds or dinosaurs, they appear to be more like the paws you would find on a mammal, rather like Suicune. I am disregarding the number of digits on the feet due to most Pokémon designs having simplified feet, but I do find it interesting that Lugia never had the impression of claws.
Now you may agree or disagree but remember that no one is right or wrong about their opinion. In the end, Lugia is whatever your mind creates and the above is simply my own theory.Previous