High-resolution UAV maps of the Gobi Desert provide new insights into the Upper Cretaceous of Mongolia.

The Gobi Desert of southern Mongolia is home to an incredibly rich record of dinosaurs and other vertebrate fossils from the latest Cretaceous Period. Together, more than a dozen sites in several basins have produced one of the richest palaeofaunas known from this interval anywhere in the world. Most of this diversity has been recovered from the fluvial deposits of the Nemegt Formation. Despite historic and ongoing research in southern Mongolia, accurate maps and geological data for the main fossil sites are still lacking, limiting our ability to investigate how local palaeoecological dynamics influenced Nemegt taxa, their geographic distribution, and their evolutionary patterns. One of these sites, Guriliin Tsav, has produced more than a hundred significant fossil specimens to date, but still remains one of the lesser known Nemegt localities. In part this is because many expeditions have instead focused on the nearby Bügiin Tsav, one of the largest and richest localities for the Nemegt Formation. To address this gap, a project was initiated in 2018 to produce a high-resolution topographic map of Guriliin Tsav using Unmanned Aerial Vehicles (UAV), and consequently, to plot the geographic and stratigraphic distributions of palaeontological resources on this map. In so doing, we also collected stratigraphic and taphonomic data from the area, allowing for the first detailed palaeoecological interpretation of Guriliin Tsav and a comparison with other localities of southern Mongolia. Here we present the results of this project, and also discuss new topographic and stratigraphic data from Bügiin Tsav. This sheds new light into the temporal and geographic distribution of vertebrate taxa in the latest Cretaceous of Mongolia. • We provide the first high-resolution maps of Guriliin Tsav, a rich Gobi Desert fossil locality. • We comprehensively describe the stratigraphy and taphonomy of the site and its impact on fossil resources. • We tabulate more than 100 fossil occurrences into the first detailed documentation of the fauna at Guriliin Tsav, showing distinct differences from sites further southeast. • We document Baruungoyot-like aeolian beds within the middle Nemegt Formation, challenging assertions that these represent sequential time intervals. • We demonstrate how channel architecture at Bugiin Tsav and Guriliin Tsav corresponds to spatial distribution of fossils. [ABSTRACT FROM AUTHOR]