The paper starts by a visit to an exhibit at the Natural History Museum in New York which shows in parallel series of fossils of horse evolution and series of how paleontologists have varied in their reconstruction of this evolution. It is the occasion to test again an argument at the heart of science studies and history of science : is there a history of science ideas about nature, or also a history of the objects known by science. If the latter is the case, then do we have the philosophical ressource to think this change of conception through ? Using James, Fleck, Whitehead and more recent science studies results, the paper tries to " desepistemologize " knowledge on the one hand while " reontologizing " it on the other.