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The Nommos were said to shapeshift into dolphins. Remember that.
Now let's look at the Yacaruna in Amazon legend.
The Yacuruna are amphibious beings can transform into an Amazon river dolphins which are attracted to the odor of blood in menstruating women. Once the woman is found, a Yacuruna will transform into a handsome and alluring man who then uses aphrodisiacs to seduce her. The children born from this were considered half-divine, because the Yacaruna were considered Gods.
This brings us to the Merovingians. They are an elite family that were said to be the bloodline of Christ, but their story is that one of their queens had sex with a sea-beast, most often called a quinotaur, while swimming. She became pregnant from this and gave birth to a king.
Now, in Basque legend, the serpentine ruler of the ocean, Sugaar, was the son of the underworld goddess Mari. Sugaar seduced a Scottish princess and she gave birth to the King of Biscay, the White Lord, Juan Zuria.