Lowland–upland migration of sauropod dinosaurs during the Late Jurassic epoch

Migrating with dinosaurs Apart from a few fossilized footprints, there is little solid evidence for dinosaur migration — until now. Comparison of the oxygen isotope ratios of sedimentary carbonates from the Morrison basin of western North America with those of carbonate from camarasaurid dinosaur teeth suggests that they drank water that fell in mountainous regions, so must have undertaken migrations between lowlands and mountainous areas about 300 kilometres apart. Sauropod dinosaurs were the largest vertebrates ever to walk the Earth, and as mega-herbivores they were important parts of terrestrial ecosystems. In the Late Jurassic-aged Morrison depositional basin of western North America, these animals occupied lowland river-floodplain settings characterized by a seasonally dry climate 1 , 2 . Massive herbivores with high nutritional and water needs could periodically experience nutritional and water stress under these conditions, and thus the common occurrence of sauropods in this basin has remained a paradox. Energetic arguments and mammalian analogues have been used to suggest that migration allowed sauropods access to food and water resources over a wide region or during times of drought or both 3 , 4 , but there has been no direct support for these hypotheses. Here we compare oxygen isotope ratios (δ 18 O) of tooth-enamel carbonate from the sauropod Camarasaurus with those of ancient soil, lake and wetland (that is, ‘authigenic’) carbonates that formed in lowland settings. We demonstrate that certain populations of these animals did in fact undertake seasonal migrations of several hundred kilometres from lowland to upland environments. This ability to describe patterns of sauropod movement will help to elucidate the role that migration played in the ecology and evolution of gigantism of these and associated dinosaurs.