Dinosaur tracks at the Nemegt locality: Paleobiological and paleoenvironmental implications

The Nemegt locality is one of the most famous dinosaur localities in Mongolia ever since the site was discovered in 1946. It yields abundant dinosaur skeletons; however, little attention had been given to dinosaur footprints at the locality. The only Nemegt dinosaur footprint study focused on descriptions of the footprints, gave only a few taxonomic implications, and provided no comparison with other dinosaur tracksites. This study reports newly recorded dinosaur footprints (hadrosaurs, sauropods, and theropods) at the Nemegt locality during the Nemegt Educational Expedition of 2016. A single footprint-bearing horizon that extends several kilometres was examined within the Nemegt Formation to determine the ichno-taxonomic assemblage of the Nemegt dinosaurs. A significant difference was identified between taxonomic compositions based on skeletal remains and ichno-taxonomic compositions based on footprints. Although the vast majority of the skeletal elements collected in the area belong to theropods, the footprints suggest that the Nemegt locality was dominated by herbivorous dinosaurs. This suggests that the previously inferred Tarbosaurus dominant taxonomic composition at the Nemegt locality is a result of a preservational bias. The size distribution of the newly studied footprints suggest that the Nemegt hadrosaurs had an adult-dominant and multigenerational population structure. Comparisons with dinosaur tracksites at the Cantwell (Alaska, USA) and Tremp (Spain) formations show that the population structure and body sizes of the Nemegt hadrosaurs were similar to those of the high-latitude Cantwell hadrosaurs. It suggests that the Nemegt area was more open and had higher plant productivity than the Tremp area.