Global map showing fossil records of the genus Daphnia and the antiquity of the subgenus Ctenodaphnia in the former Laurasia. Circles indicate fossil records of Daphnia colored by subgenus (Ctenodaphnia is red and Daphnia s. str. is blue). The grey shaded continents indicate the former Gondwanaland regions and the unshaded regions represent the former Laurasia regions. Red shading in North America indicates the present day distribution of the basal Ctenodaphnia from phylogenetic and morphological information.