A new medium−sized rebbachisaurid sauropod from the Castrillo la Reina Formation (Upper Barremian-Lower Aptian)

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 it more 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 stem taxon 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.

Abnormalities in the histo- and ultrastructure of the amniote eggshell are often related to diverse factors, such as ambient stress during egg formation, pathologies altering the physiology of the egg-laying females, or evolutionarily selected modifications of the eggshell structure that vary the physical properties of the egg, for example increasing its strength so as to avoid fracture during incubation. When dealing with fossil materials, all the above hypotheses are plausible, but a detailed taphonomical study has to be performed to rule out the possibility that secondary processes of recrystallization have occurred during fossilization. Traditional analyses, such as optical microscopy inspection and cathodoluminescence, have proven not to be enough to understand the taphonomic story of some eggshells. Recently, electron backscatter diffraction has been used, in combination with other techniques, to better understand the alteration of fossil eggshells. Here we present a combined study using scanning electron microscopy, optical microscopy, cathodoluminescence and electron backscatter diffraction of eggshell fragments assigned to Megaloolithus cf. siruguei from the Upper Cretaceous outcrops of the Cameros Basin. We focus our study on the presence of secondary shell units that mimic most aspects of the ultrastructure of the eggshell mammillae, but grow far from the inner surface of the eggshell. We call these structures extra-spherulites, describe their crystal structure and demonstrate their secondary origin. Our study has important implications for the interpretation of secondary shell units as biological or pathological structures. Thus, electron backscatter diffraction complements other microscope techniques as a useful tool for understanding taphonomical alterations in fossil eggshells.

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Terra Nova, 24, 136–141, 2012 Abstract Theropod dinosaur footprints at the Costalomo tracksite (Pinilla de los Moros Formation, Upper Hauterivian–Lower Barremian, western Cameros Basin, Salas de los Infantes, Burgos Province, Spain) show unusual preservation of a previously undescribed nature. The footprints occur as casts (positive epireliefs) at the top of a sandstone bed and preserve exceptional details of the top of the digit and claw morphology, and of digital interactions with the sediment during penetration and extraction from the sediment. Footprint formation and preservation occurred in the following stages: (1) The dinosaur stepped on a thin (4–8 cm thick) mud layer, its foot sinking to contact an underlying sand layer (channel fill); (2) voids left in the cohesive mud after foot withdrawal were later filled with sand; (3) subsequent deposition, burial and Alpine compression indurated the muds and the sands of both the footprint casts and the underlying channel sand layer; and (4) modern erosion exposed the footprint casts, by removing the mud above the sandstone.

The sauropod of El Oterillo II is a specimen that was excavated from the Castrillo de la Reina Formation (Burgos, Spain), late Barremian–early Aptian, in the 2000s but initially remained undescribed. A tooth and elements of the axial skeleton, and the scapular and pelvic girdle, represent it. It is one of the most complete titanosauriform sauropods from the Early Cretaceous of Europe and presents an opportunity to deepen our understanding of the radiation of this clade in the Early Cretaceous and study the paleobiogeographical relationships of Iberia with Gondwana and with other parts of Laurasia. The late Barremian–early Aptian is the time interval in the Cretaceous with the greatest diversity of sauropod taxa described in Iberia: two titanosauriforms, Tastavinsaurus and Europatitan; and a rebbachisaurid, Demandasaurus. The new sauropod Europatitan eastwoodi n. gen. n. sp. presents a series of autapomorphic characters in the presacral vertebrae and scapula that distinguish it from the other sauropods of the Early Cretaceous of Iberia. Our phylogenetic study locates Europatitan as the basalmost member of the Somphospondyli, clearly differentiated from other clades such as Brachiosauridae and Titanosauria, and distantly related to the contemporaneous Tastavinsaurus. Europatitan could be a representative of a Eurogondwanan fauna like Demandasaurus, the other sauropod described from the Castrillo de la Reina Formation. The presence of a sauropod fauna with marked Gondwananan affinities in the Aptian of Iberia reinforces the idea of faunal exchanges between this continental masses during the Early Cretaceous. Further specimens and more detailed analysis are needed to elucidate if this Aptian fauna is caused by the presence of previously unnoticed Aptian land bridges, or it represents a relict fauna from an earlier dispersal event.

In recent decades a unique association of basal neosauropod and turiasaur sauropods has been described from the Jurassic-Cretaceous transition of Spain. In this context, a sauropod femur from the Tithonian-Berriasian is studied for the first time. The femur in question is an isolated specimen, recovered from the Tera Group in Tera (Soria). It displays a unique mosaic of derived characters as yet undescribed in femora of the Upper Jurassic and Lower Cretaceous of Spain. A prominent lateral bulge, high eccentricity, and a lateromedially flattened proximal end link the femur from Tera with Titanosauriformes. Moreover, it presents a significant distal projection of the tibial condyle, a character observed in Asiatic Titanosauriformes of the Lower Cretaceous. The femur from Tera adds a fifth sauropod taxon to the Tithonian-Berriasian of Spain, and, for the first time, a representative of Titanosauriformes.

The Las Sereas site includes at least 14 ichnological outcrops along 5.6 km, in the Lara area, southwest Burgos Province. 67 ichnites of dinosaurs are documented at Las Sereas 7, identified as theropod and sauropod trackways occurring in shallow carbonates of lacustrine environment. Sauropod trackways have intermediate-gauge and low heteropody, and show different anatomical features to other tracks found in the ichnological record, especially in the disposition and orientation of pes digits. They are similar to Polyonyx from the Middle Jurassic of Portugal. However, since they do not preserve reliable manus data they are classified as aff. Polyonyx. The three sauropod trackways are related to the same kind of trackmaker. They differ from each other only in size, and gregarious behavior has not been detected. Analysis of these trackways reveals changes in travel direction even when there are few tracks in each sequence. At the Las Sereas 7 tracksite, the pace length (PL), width of the angulation pattern (WAP) and the WAP/PL ratio and depth analysis via photogrammetry show a direction change in two sauropod trackways. This tracksite and that at La Pedraja are unique in the Tithonian-Berriasian interval of the Iberian Peninsula that occur in a lacustrine environment, and could be indicate of the relationship between the diversity of Iberian, Tithonian-Berriasian sauropod tracks and sedimentary environments.Keywords: Dinosaurs, Sauropod tracks, Tithonian, Berriasian, Cameros Basin, Iberia Resumen El yacimiento de Las Sereas se compone de al menos 14 afloramientos icníticos que se localizan a lo largo de 5,6 Km de longitud en la comarca de Lara, en el sureste de la provincia de Burgos. En el afloramiento de Las Sereas 7 se han documentado 67 icnitas de dinosaurios, identificadas como terópodas y saurópodas, producidas en un ambiente lacustre carbonatado somero. Las rastros saurópodos son de anchura intermedia y heteropodia baja mostrando caracteres anatómicos diferentes a los encontrados en el registro icnológico conocido, en especial en lo referente a la disposición y orientación de los dedos del pie. La mayor semejanza de estas icnitas saurópodas se establece con Polyonyx del Jurásico Medio de Portugal, pero al carecer de datos fiables sobre la anatomía de las manos en Las Sereas, clasificamos estas icnitas de Burgos como aff. Polyonyx. Los tres rastros saurópodos de Burgos se atribuyen a un mismo icnopoyeta, diferenciándose entre sí sólo por el tamaño, y sin que se haya detectado un comportamiento gregario. En el estudio de estos rastros pueden recogerse datos que informen sobre trayectos con cambio de dirección, incluso cuando lo que se conserva es una serie relativamente corta de pasos. En Las Sereas 7 la combinación de los valores de varios parámetros -longitud de paso (PL), pauta de anchura de angulación (WAP) y relación WAP/PL -y el estudio de la profundidad de las icnitas por fotogrametría permiten interpretar un cambio de dirección en dos de los rastros saurópodos. Este yacimiento y el de La Pedraja...