No unambiguously paleognathous fossil birds are known until the Cenozoic (though birds occasionally interpreted as lithornithids occur in Albian appalachian sites ), but there have been many reports of putative paleognathes, and it has long been inferred that they may have evolved in the Cretaceous. Given the northern hemisphere location of the morphologically most basal fossil forms (such as "Lithornis", "Pseudocrypturus", "Paracathartes" and "Palaeotis"), a Laurasian origin for the group can be inferred. The present almost entirely Gondwanan distribution would then have resulted from multiple colonisations of the southern landmasses by flying forms that subsequently evolved flightlessness, and in many cases, gigantism.