Although few of the most ancient species have left modified descendants, yet, at remote geological periods, the earth may have been almost as well peopled with species of many genera, families, orders and classes, as at the present day.
Nahiz eta espezie zaharrenetariko gutxik utzi duen ondorengo eraldaturik, geologi aro urrunetan lurra egun bezain populaturik egon zitekeen genero, familia, ordena eta klase askotako espeziez.