Long-necked dinosaurs called sauropodomorphs originated in the Southern Hemisphere during the mid to late Triassic period, some 230 million years ago. From there, they dispersed to all early continents, but there is some debate as to how. Some have assumed that a single taxon dispersed widely across the Pangaea supercontinent and diversified later. But Timothy Rowe at the University of Texas at Austin and his colleagues argue that this ubiquitous 'cosmopolitan' dinosaur never existed.

Credit: R. SOC

They recently described a new taxon named Sarahsaurus (fossil veterbrae pictured), found in Arizona, and analysed its relationships to other North American sauropodomorphs. Their analysis suggests separate arrivals for different groups. Geographical isolation events, extinctions and dispersal happened multiple times throughout the Mesozoic period, they argue.

Proc. R. Soc. B doi:10.1098/rspb.2010.1867 (2010)