In addition, the molecular data suggest that the Cracidae originated in the Late Cretaceous, but the authors caution that this cannot be more than a hypothesis at present: as the rate of molecular evolution is neither constant over time nor uniform between genera and even species, dating based on molecular information has a very low accuracy over such long timespans and needs to be corroborated by fossil evidence. The fossil record of cracids is limited to a single doubtfully distinct genus of chachalaca, "Boreortalis" (Hawthorn Early Miocene of Florida, USA; may actually be a junior synonym of "Ortalis") and some species in the modern genus "Ortalis", however. This does not provide any assistance in evaluating the hypothesis (Pereira "et al.", 2002) that the split between the 4 main lineages of our time occurred quite rapidly, approximately in the Oligocene or slightly earlier, somewhere between 40 and 20 mya.