Question

insert one comma to separate the coordinate adjectives.
,
considered both a continent and a country, australia is home to numerous native species of plants and animals. incredibly, more than eighty percent of these remarkable unique inhabitants are found solely in australia.

Explanation:

Coordinate adjectives "remarkable" and "unique" describe "inhabitants" and can be separated by a comma. We insert a comma between them.

Answer:

Incredibly, more than eighty percent of these remarkable, unique inhabitants are found solely in Australia.