Phylogeny and paleobiogeography of Triassic Sauropterygia: problems solved and unresolved

This comparison of the geographic and stratigraphic distribution of the secondarily marine stem-group sauropterygian reptiles from the Triassic with the phylogenetic relationships within this group indicates an incompleteness of the fossil record for the clade of almost 50%, which limits the reconstruction of the biogeographical history of its component taxa. Given their restriction to nearshore habitats or shallow epicontinental seas, it is unlikely that stem-group sauropterygians had the capacity for trans-oceanic dispersal. Dispersal along coastlines may have been a component of their biogeographical history, however, as is indicated by the immigration of sauropterygians into the Anglo-Germanic basin at the transition of the Lower to Middle Triassic, and by the population of the Alpine Triassic by sauropterygians after the evolution of the appropriate intraplatform basin habitat during the Middle Triassic. Conversely, trans-Panthalassan relationships of pistosaur sauropterygians appear best explained as a consequence of vicariance due to the accretion of exotic terranes at opposite margins of the Pacific Basin. A vicariant event resulting from the opening of the southern branch of the Neotethys may also account for the sister-group relationships of nothosaurs from the northern Gondwanan shelf and the Anglo-Germanic basin.