Enigmatic tracks of solitary sauropods roaming an extensive lacustrine megatracksite in Iberia

Sauropod remains are abundant on the Iberian Peninsula across the Jurassic-Cretaceous transition. Where the osteological record shows a high diversity of this kind of dinosaur, the ichnological findings are mainly limited to sauropod tracks characterized by kidney-shaped manus (with or without pollex impressions) and pes impressions with three claw imprints oriented laterally. Here, we present a new sauropod ichnotaxon, Iniestapodus burgensis, found at several exposures within the Las Sereas megatracksite (Burgos, Spain). These are preserved within lacustrine limestone strata of the Rupelo Formation (Tithonian-Berriasian). Iniestapodus burgensis is characterized by: semicircular manus tracks with small pollex impressions; unusual tetradactyl pes tracks with evidence of four claws oriented anteriorly (I-II) and laterally (III-IV), of variable sizes (short claw I and IV impressions, claw II and III being the largest). The combination of features and comparison with the osteological record allows us to propose a non-titanosaurian titanosauriform as a possible trackmaker. All the Iniestapodus tracks are represented by at least two different size classes of small and medium-sized individuals, and their trackways show different multidirectional orientations. The paleoenvironmental and paleoecological data suggest that Iniestapodus trackmakers were solitary individuals, likely representing different age classes, that crossed and used the Las Sereas shallow lacustrine-palustrine areas as their preferred habitat

The Jurassic – Cretaceous transition in the West Cameros Basin (Tera Group, Burgos, Spain): Sedimentological and palynostratigraphical insights

The Jurassic–Cretaceous boundary transition is widely distributed within the West Cameros Basin. This horizon is constituted by the Tera Group, consisting of two depositional sequences (DS1 and DS2) comprising four geological formations spanning the Tithonian to the Berriasian. Here, a combined sedimentological and palynostratigraphic study was made covering the Tera Group. The sedimentological results for the DS 1 differentiate three facies associations (FA 1-1, 1-2 and 1-3) corresponding to floodplains and braided channels of a distributive fluvial system shifting to shallow lacustrine facies in a semi-arid climate. For the DS 2, three FA were also differentiated (FA 2-1, 2-2, and 2-3), corresponding to tidal-influenced meandering channels and floodplains in a distal fluvial to a delta-plain system that shifts to shallow lacustrine facies. The palynological results were only productive in samples from the Jaramillo Formation. The palynological record shows an assemblage dominated by spores including Concavissimisporites, Leptolepidites and Taurocusporites, as well as Classopollis pollen. According to the stratigraphic ranges of some selected taxa, the suggested chronostratigraphic assignment is lower Berriasian for the Jaramillo Fm. A comparison of the microfloras from the Tithonian–Berriasian recorded in the Iberian Peninsula was carried out. The following observations can be concluded: 1) the change in the plant communities, already observed since the Late Jurassic onwards, became more pronounced between the Tithonian–Berriasian boundary and the late Berriasian; and 2) a noteworthy occurrence of some biostratigraphically important taxa, specifically for the Tithonian–Berriasian interval

A dentary fragment of an iguanodontoid ornithopod (Dinosauria) from the Early Cretaceous of Salas de los Infantes (Burgos, Spain) in the collections of the Institut für Geowissenschaften of Tübingen (Germany)

A dentary fragment that preserves several teeth in situ of an ornithopod dinosaur from the Lower Cretaceous of Salas de los Infantes (Burgos, Spain) is described. The general aspect and the conservation of the rock associated with the fossil suggest that it would come from the Pinilla de los Moros Formation (upper Hauterivian-lower Barremian). The material takes part, together with other fossils of dinosaurs and crocodilians, of a collection gathered at the end of the 1960’s and deposited nowadays in the Institut für Geowissenschaften of the University of Tübingen (Germany). The dentary teeth exhibit a distal primary ridge and a mesial secondary ridge, as typically in basal iguanodontoids. Nevertheless, some teeth show a single subcentral carina and lack subsidiary ridges, as in hadrosaurids. Unlike hadrosaurids, however, the Salas specimen has probably one functional tooth and one replacement crown per dentary tooth position, retaining the plesiomorphic state present in basal iguanodontoids. Due to the fragmentary nature of the material, it is provisionally assigned to Iguanodontoidea inde

Histogenesis and growth dynamics of the tiny Vegagete rhabdodontomorph hindlimb (Ornithischia, Ornithopoda): Paleoecological and evolutionary implications

The Vegagete rhabdodontomorph is an as-yet unnamed ornithopod known from tiny and fragmentary remains, and was collected in the upper Barremian–lower Aptian of the Salas de los Infantes municipality (Burgos Province, Spain). As the earliest known rhabdodontomorph and a stem member of the lineage leading to Rhabdodontidae, this animal is key to better understanding growth within basal Iguanodontia. To do so, we prepared histological thin-sections of a sample of differently sized femora and tibiae. Here we combined anatomical, micro-anatomical and histological observations to analyse the growth and life-history traits of this little animal, and reinterpreted growth and postural shifts within the broader evolutionary framework of Rhabdodontomorpha. We find that the largest Vegagete ornithopod individual was a late subadult, making it the smallest ornithopod ever recovered. This taxon would have shifted from a quadrupedal stance to a bipedal one at a juvenile stage. In sharp contrast, Late Cretaceous rhabdodontids would retain the juvenile quadrupedal stance of their ancestors, and maintain quadrupedality until their adulthood most probably through progenetic development. No sampled Vegagete ornithopod individual shows Lines of Arrested Growth (LAGs). However, a minimal age greater than one year is most likely. Given the many signs of histologic maturity, the absence of LAGs is here interpreted as uninterrupted, fast growth of the hindlimbs. This taxon would probably not have been able to endure long distance running. Instead, its small size and relatively long legs would have been beneficial to rapidly escape and hide from predators.Fil: Dieudonné, Paul-emile. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Fernández Baldor, Fidel Torcida. No especifíca;Fil: Stein, Koen. Vrije Unviversiteit Brussel; Bélgic

EBSD data from Moreno-Azanza et al., 2016. Combined use of electron and light microscopy techniques reveals false secondary shell units in Megaloolithidae eggshells

S1. Raw EBSD data of PS-TEC,21

An unexpected early rhabdodontid from Europe (Lower Cretaceous of Salas de los Infantes, Burgos Province, Spain) and a Re- Examination of basal iguanodontian relationships

Disarticulated and incomplete remains from a new diminutive ornithopod are described. They come from the Cameros Basin in the north of Spain and were collected from the red clays of the Castrillo de la Reina Formation, ranging from Upper Barremian to Lower Aptian. The new ornithopod described here is slender and one of the smallest ever reported. An up-to-date phylogenetic analysis recovers this taxon as a basal iguanodontian. Its unique combination of characters makes itmore derived than slender ornithopods like Hyphilophodon and Gasparinisaura, and bring very interesting insights into the basal iguanodontian phylogeny. Though possessing a minimum of three premaxillary teeth, this taxon also bears an extensor ilio-tibialis groove on the distal part of its femur. Moreover, its dentary and maxillary teeth are unique, remarkably similar to those regarded as having a "rhabdomorphan" affinity. This unknown taxon is suggested to be a stemtaxon within Rhabdodontidae, a successful clade of basal iguanodonts from the Late Cretaceous of Europe. The Gondwanan ornithopods share the strongest affinities with this family, and we confirm Muttaburrasaurus as a sister taxon of the Rhabdodontidae within a newly defined clade, the Rhabdodontomorpha.Fil: Dieudonné, Paul Emile. Universidad de Zaragoza; EspañaFil: Tortosa, Thierry. Réserve Naturelle Nationale Sainte-Victoire; FranciaFil: Fernández Baldor, Fidel Torcida. Municipio de Salas de los Infantes. Museo de Dinosaurios; EspañaFil: Canudo, José Ignacio. Universidad de Zaragoza; EspañaFil: Díaz Martínez, Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentin