Dinosaurian paleobiogeography. (C) Polar dispersal across Beringia (double-headed arrow) must be invoked to explain the geographic distribution of ceratopsians and other dinosaurian subgroups during the Late Cretaceous. Checkered branches show dispers- al from Asia to North America in three lineages, which is one of two equally parsimonious dispersal scenarios for ceratopsians (given this cladogram and an Asian origin for Ceratopsia). Globe shows Maastrichtian (70 Ma) paleogeography divided into orogenic belts (inverted Vs), lowlands (black), and shallow and deep seas (gray and white, respectively). Internal branch lengths of the cladogram are scaled according to the number of supporting synapomorphies under delayed character-state transformation. Scale bar indicates 10 synapomorphies (with the long ceratopsid branch shortened). 1, Psittacosaurus; 2, Chaoyangsaurus; 3, Leptoceratops; 4, Udanoceratops; 5, Microceratops; 6, Bagaceratops; 7, Protoceratops; 8, Montanoceratops; 9, Turanoceratops; 10, Chasmosaurinae; 11, Ceratopsinae.