I have a theory about El Dorado. In the beginning, what is now called El Dorado was part of skull island,a huge land mass, along with all of the other islands of that world. The aztecasaurs lived there before everyone else, but they can't build cities if they can't touch their faces, so they called upon the water moles, who revered them as gods, to be their slaves.

The water moles built their pyramids and temples, and also mined all their gold, which they used to build El Dorado. Thats why those aztecasuar wheels relate to El Dorado.

Unfortunately, the Volcano! erupted, causing the islands to drift apart. The aztecasaur golden age ended and they fled to their main cities, Xol Amul and El Dorado. The race split into two tribes: the Xol Amul's and the El Dorado's. The El Dorado's became extremely protective of their land and may be the "dangers" Marco Pollo speaks of.

Fearless Finnagan lvl 60
Gruesome Griffin lvl 30

I like your theory mate! I would definitely go with this theory!