Non-invasive imaging reveals new cranial element of the basal ornithischian dinosaur Laquintasaura venezuelae, Early Jurassic of Venezuela

We report and describe the new left premaxillary bone of the basal ornithischian Laquintasaura venezuelae coming from a bonebed of the La Quinta Formation in the Andes of Venezuela. Previous dating of the bonebed based on U-Pb zircon analysis suggested an earliest Jurassic (Hettangian) maximum age. To our knowledge, for the first-time high-resolution computer tomography scanning was applied to rocks of this site to search for fossils, leading to the discovery reported here and the promise of this method to cope with unprepared blocks from the same site. We created a three-dimensional model of the fossil and show that the left premaxilla of L. venezuelae presents the unusual characteristic of a seven dental grooves count. This number is known only in other two basal thyreophorans such as Huayangosaurus taibaii and Gargoyleosaurus parkpini. This is consistent to the general trend reported for ornithischian evolution to lose premaxillary teeth, which suggests that Laquintasaura represents the plesiomorphic state of the character, with a high tooth count. Only with new anatomical data on Laquintasaura can we generate robust hypothesis of its evolutionary relationships, which address some of the earliest history of dinosaurs and their occurrence in the otherwise poorly documented equatorial areas of the globe.