In this article I analyze assertive epistemic modality (expression of certainty) in a series of scientific news reports on the paleontological discovery of the so-called Hombre of Orce, published in El País between 1983 and 1977. The discovery of a small skull fragment was initially attributed to the oldest hominoid found in Eurasia, yet later analyses indicated that it might really be from an equidae. I describe linguistic forms of the lexical type, the semantic contents (credibility, verification, conviction and confirmation) as well as the social and epistemological rhetorical functions of modalizers such as tajantemente, verificación, cre e r, ratificar, poder afirm a r. The study reveals that in the analyzed corpus these markers of certainty are mainly used to transmit confidence and reliability to the reader in the case of the strongly refuted thesis.