Los titanosaurios de la Formación Villalba de la Sierra en la XXIV Bienal de la Real Sociedad Española de Historia Natural

Durante la semana pasada estuvimos en la XXIV Bienal de la Real Sociedad Española de Historia Natural celebrada en Valencia, donde presentamos una comunicación oral sobre los dinosaurios saurópodos titanosaurios de la Formación Villalba de la Sierra. Esta comunicación titulada “Titanosaurian sauropods from the Upper Cretaceous of Villalba de la Sierra Formation (Spain)”, tiene como objetivo evaluar el actual estado de conocimiento del registro de este grupo en dicha formación, y presentar varios de los más recientes hallazgos e información procedente del yacimiento de Lo Hueco (Cuenca) y Poyos (Guadalajara).

The sedimentary sequence of the Villalba de la Sierra Formation is located at the southwestern branch of the Iberian Ranges, being early Campanian to middle? Eocene in age. The titanosaurian fossil record from the upper Campanian-lower Maastrichtian levels is abundant and diverse. In recent years, two important fossil localities have been discovered, Lo Hueco (Fuentes, Cuenca) and Poyos (Sacedón, Guadalajara). Lo Hueco represents a multitaxic bonebed, which has yielded more than 10,000 fossils of which nearly half corresponds to titanosaurian remains, including several partial skeletons, mostly articulated or with low dispersion. This record is important to understand the evolutionary history of the Ibero-Armorican titanosaurs and to study the intraspecific variability and paleobiology of these European sauropods, using a set of new methodologies including 3D-geometric morphometrics, CT scanning and paleohistology. Preliminary comparisons indicated the presence of at least two titanosaurian morphotypes based on two types of cranial morphologies, teeth, and appendicular bones; however, higher diversity have been proposed in recent works based on the axial skeleton. In 2016, Lohuecotitan pandafilandi was the first established taxon for this Formation; and the holotype of Lohuecotitan was found partially articulated including cervical, dorsal, sacral, and caudal vertebrae, ribs, chevrons, and several appendicular elements. This taxon was considered a member of Lithostrotia. Recent analyses are proposing two different scenarios for its phylogenetic position: 1) early branching member of Lithostrotia; or 2) member of Lirainosaurinae. The detailed description of Lohuecotitan (in progress) is revealing the presence of shared features with the titanosaur Paludititan, from the Maastrichtian of the Haţeg Basin (Romania). Here, we briefly present seven new partial individuals (HUE-EC-02, HUE-EC-03, HUE-EC-04, HUE-EC-05, HUE-EC-06, HUE-EC-11 and HUE-EC-13) that are providing relevant information for codification and scoring of morphological characters. The new locality of Poyos is also yielding new titanosaurian material (eggs and bones) from the same Formation. At least three partial individuals have been identified, which seem to preserve a set of features not recorded in Lo Hueco. Our preliminary phylogenetic analyses recovered Lohuecotitan, HUE-EC-02 and Paludititan as possible members of Lirainosaurinae together with Lirainosaurus, from the upper Campanian-Maastrichtian site of Laño (Treviño County), and Ampelosaurus and Atsinganosaurus, from the Upper Cretaceous of southern France. Lirainosaurinae is recovered as an early branching clade of Saltasauridae. In conclusion, the titanosaurian diversity recorded in Villalba de la Sierra is represented by three to five taxa: at least two different forms in Lo Hueco, and one in Poyos. However, the presence of up to four different taxa in Lo Hueco and the presence of shared taxa in both sites is not ruled out.