NEW VISUALIZATIONS OF THE THREE-DIMENSIONAL, TERRESTRIAL WORLD OF THE “DRAGON REPTILES”:PTEROSAUR TRACKS AND PHOTOGRAMMETRIC ICHNOLOGY

For nearly 170 years following the discovery of the first pterosaur fossils in Germany's Solnhofen Limestone, the understanding of pterosaur terrestrial locomotion was based primarily on fossil misidentifications and skeletal anatomy research. This changed in 1952, when Utah geologist William Lee Stokes discovered an enigmatic trackway on a small fluvial sandbar in the Saltwash Member of the Upper Jurassic Morrison Formation in the Carrizo Mountains of northeastern Arizona. Stokes suggested that these “dragon reptile” tracks were new to science (i.e., Pteraichnus saltwashensis) and were the first direct evidence of pterosaurs walking on land, as well as being only the second pterodactyl fossils from the Jurassic of the Western Hemisphere. Since this discovery, thousands of similar traces have been found on nearly every continent, yet Stokes’ specimen and description of the 9 consecutive pairs of tridactyl manus and tetradactyl pes prints have remained the “gold standard” for all pterosaur track research. Unfortunately, many researchers have not looked at the original fossil, subsequently repeating or compounding subtle errors from Stokes’ 1957 manuscript; leading to mistakes in interpretation and identification. Reexamination of the ichnoholotype Pteraichnus saltwashensis (UMNH VP 50) at the Natural History Museum of Utah with state-of-the art, photogrammetric documentation techniques, allows for the subtle details of pterodactyloid locomotion and ichnotaxonomy to be teased out of this unique ichnite. This permanent, high resolution, 3D digital data set supports a wide variety of analyses and enhanced visualizations of the track-bearing surface. From the position and differential preservation of the tracks, their degree of indentation, and variable gait (related to slope and moisture content of the substrate), it appears the track-making pterosaur was walking on a sand bar parallel to and near the edge of a stream. In addition, several footprints are impacted by overprinting, which in turn fall in areas where the track blocks are cracked or missing. Close-range photogrammetric studies have assisted in the recordation of the ichnological features, measurements, and geometry of these traces, allowing for kinetics of movement and terrestrial behaviors to be derived from this significant fossil.