High-latitude dipnoan aestivation burrows suggest seasonal aridity for early dinosaur ecosystems in the Late Triassic of East Greenland

It has been proposed that arid conditions across certain regions in Pangea limited the migration of herbivorous dinosaurs. However, there is conflicting evidence about the prevailing climatic conditions in northern Pangea, an area inhabited by large sauropodomorphs from the mid-Norian. Here we describe large burrows from the upper part of the Fleming Fjord Group in Jameson Land, East Greenland. They consist of vertical to slightly inclined burrows, up to 60 cm long and 5–10 cm wide, with slightly enlarged terminal chambers. The burrows are identified in mudstone sequences at two separate sites that represent the same interval of the Ørsted Dal Formation. The burrows are unbranched, largely devoid of scratch marks, and have no mud or lag linings. Their large size indicates a vertebrate producer, and due to their morphology and architecture, we interpret them as dipnoan fish aestivation burrows – a shelter in an environment that occasionally dried up. The newly discovered trace fossils lead us to following conclusions: (1) aestivation behaviors were more common amongst non-lepidosirenid lungfish than previously assumed, (2) a seasonally dry climate persisted in the Jameson Land Basin throughout the latest Norian, (3) sauropodomorphs and theropods inhabited the area despite the dry conditions, and thus (4) the spatial distribution of sauropodomorphs was perhaps controlled by factors other than aridity or, alternatively, they migrated to this area only seasonally.