Lets talk Tonberries! (Spoilers)

[Malrend]

Well the description of how the disease progressed, ears, nose, and lips rotting away, limbs growing shorter, and skin turning green, could apply to every race, although there would likely be a size discrepancy between the individual Tonberries.

Also the fall of Nym was 1500 years ago, that would be.. The early 5th Astral Era, I think.. At that point most of the races on Eorzea were likely still separating themselves from the others. I seem to recall that the end of the Hyur-Elezen wars, was the beginning of the coexistence between races.. And I don't believe that would have taken place yet, by the time of Nym's fall.

[Chaako]

Well the description of how the disease progressed, ears, nose, and lips rotting away, limbs growing shorter, and skin turning green, could apply to every race

Doesn't explain the fish tail though.

[Malrend]

Doesn't explain the fish tail though.

Well we were informed that in an effort to kill those infected with this disease, the healthy Nymians flooded the quarantined sections of their flying cities.
It is a bit of a stretch, but the tail-fins might be an evolutionary reaction to being submerged for a good amount of those 1500 years that have passed since then.