I have to ask, is there any connection between Cool Ranch and Aquila? I notice that they are both mainly bird species characters, and I wonder if they perhaps evolved from each other at some point?
What do you guys think?

That's true, but you know chickens may possibly have descended from dinosaurs. So I wouldn't be so quick to assume there.

Ah, they are all lost descendants of the Aztecans.

Well, the chickens come from back east, as said prior. That's just a reference to the westward expansion of settlers in North America. Probably, the chickens come from another skyway in Cool Ranch. Considering Avernus and Marleybone, it seems that skyways aren't necessarily all interconnected in a world. Avernus is a single contained skyway, as far as we know. Marleybone City seems to have it's own skyway that is unconnected from Westminster, although perhaps one day we will travel the Thames.

As for evolution from the Eagles. I'd point out something called convergent evolution. Where two or more species evolve to a similar appearence/function from two separate unrelated ancestors due to similar habitats and environments. This gives rise to analogous forms, instead of homologous forms. (Although sometimes, an analogous form can also be an homologous form) the most commom real world examples are dolphins compared to sharks, and bats compared to birds.

CdeWinter on Apr 27, 2017 wrote:

Well, the chickens come from back east, as said prior. That's just a reference to the westward expansion of settlers in North America. Probably, the chickens come from another skyway in Cool Ranch. Considering Avernus and Marleybone, it seems that skyways aren't necessarily all interconnected in a world. Avernus is a single contained skyway, as far as we know. Marleybone City seems to have it's own skyway that is unconnected from Westminster, although perhaps one day we will travel the Thames.

As for evolution from the Eagles. I'd point out something called convergent evolution. Where two or more species evolve to a similar appearence/function from two separate unrelated ancestors due to similar habitats and environments. This gives rise to analogous forms, instead of homologous forms. (Although sometimes, an analogous form can also be an homologous form) the most commom real world examples are dolphins compared to sharks, and bats compared to birds.

Back east makes a nice reference to settling North America, but could also refer to Mooshu, too, as the Far East. I think the eagle/ chicken relationship is a bit closer than the ones you mentioned. They are both birds. Even ostriches and humming birds, as dissimilar as they are, are closer to each other than to a bat. Underneath the feathers, they share much in common, beaks, egg laying, no milk, hollow bones (the ostrich has some hollow bones, though less so than many other birds).
For Anecorbie: What's wrong with saying that piranha and goldfish are similar because they are fish? Scales, gills, swim bladders, etc, sounds like many similarities.
I like the idea of the horses and unicorns being related.