The EU had an explanation for this (of course) wherein there are two different types of Gungan, one being the Jar Jar kind and the other being the Boss Nass kind.
But why does Boss Nass need and explanation? He’s just fatter than the other Gungans. Tarpals on the other hand actually has a unique feature.
Because that’s how the old EU (slightly less so the new EU) worked, everything had to have a detailed exacting explanation even if they had to retcon or shoehorn it in. Usually they were dumb.