Cracraft (2001) gave a comprehensive review to the data and strongly supported the Gondwana vicariance hypothesis with phylogenetic evidence and historical biogeography. He cites molecular clock studies that show a basal divergence date for neornithes being around 100 Mya. He credits the authors of the molecular clock studies with the observation that the lack of southern paleognath fossils may correspond to the relatively scarce southern Cretaceous deposits, and the relative lack of paleontological field work in the southern hemisphere. Moreover, Cracraft synthesizes the morphological and molecular studies, noting conflicts between the two, and finds that the bulk of the evidence favors paleognath monophyly. He also notes that not only the ratites, but other basal groups of neognathous birds, show trans-Antarctic distribution, as would be expected if the paleognaths and neognaths had diverged in Gondwana.