A: Because they were described in detail before they were even discovered.
So predictable are the adaptations for life underground, that in 1974 the zoologist Richard D. Alexander of the University of Michigan predicted the existence of a kind of social mammal not then known to exist. On the basis of his knowledge of social insects, Alexander made twelve predictions about the hypothetical mammal. It would live somewhere in Africa; it would have a morphologically distinct queen; it would live on tubers; it would engage in "cooperative reproduction"; and so on. Alexander then went looking tor the predicted creature and helped discover and study it in the semideserts of Ethiopia and Kenya. The animal is now known as the naked mole rat (Heterocephalus glaber).
Wow! That is amazing. Surely this can be developed; there must be other examples in other sciences ... I suppose "dark matter" is one example, is it? When it's found, it'll be as a result of looking for something that they knew must be there. Is the continent of America another example?