Leviathan Class Organisms

Soooo. I was playing the other night and found a spikey stone looking egg amongst some sand shark eggs. Come to fine out, it was a sea dragon leviathan egg. I had no inventory room at the time and can't for the life of me remember where I found it. I have no idea if this was a glitch or what, but I have heard rumors about obtainable leviathan class eggs. Anyone else find one by accident? I'm on xbox one s.