Urbión Group

The Urbión Group is a geological group in Castile and León and La Rioja, Spain whose strata date back to the Early Cretaceous (late Hauterivian to late Barremian. The formations of the group comprise a sequence of brown limestones in a matrix of black silt, sandstones, claystones and conglomerates deposited under terrestrial conditions, in alluvial fan and fluvial environments.

Dinosaur remains are among the fossils that have been recovered from the formation.

Description
The Urbión Group, named after the Picos de Urbión, comprises a sequence of brown limestones in a matrix of black silt, sandstones, claystones and conglomerates deposited under terrestrial conditions, in alluvial fan and fluvial environments.

The contact with the overlying Enciso Group is exposed at the Presa Enciso tracksite.

Demandasaurus darwini
The fossil bones of Demandasaurus were recovered in the "Tenadas de los Vallejos II" quarry, located 10 km southwest of the town of Salas de los Infantes (Province of Burgos, northern Spain). In geological terms, this area lies within the western Cameros Basin, which is located in the north−westernmost part of the Iberian Range, outcropping in the provinces of Burgos, Soria and La Rioja. This basin is one of the most subsident basins formed during the rift interval at the end of the Jurassic and the Early Cretaceous, which affected this part of the Iberian Peninsula.

The sediments of the Tenadas de los Vallejos II quarry belong to the Castrillo de la Reina Formation and comprise red clay beds intercalated with sheet−like sandstone channel fills that are interpreted as floodplain and fluvial channel deposits respectively. The fluvial system of the Castrillo de la Reina Formation shows a braided channel pattern with well developed and drained floodplains. This lithostratigraphic unit belongs to the fifth depositional sequence of the six ones that divide the basin. The age of the fifth depositional sequence is Late Barremian to Early Aptian as is suggested by charophyte and ostracod biostratigraphy.

The Tenadas de los Vallejos II site was discovered in 1999 during prospection work carried out by the Archaeological−Palaeontological Group of Salas de los Infantes (Colectivo Arqueológico−Paleontológico de Salas de los Infantes, CAS).

Ten caudal vertebrae, a haemal arch, two ischia and a femur, as well as bone fragments were collected in the site. Excavations were carried out during the years 2002–2004, covering a surface area of some 240 m2. Approximately 810 skeletal elements and bone fragments were recovered, and most of them belong to a single specimen of rebbachisaurid sauropod. The remains were found disarticulated in the same bed and in close proximity to each other. The neural arches of the vertebrae are firmly co−ossified to the centra. There are no anatomically repeated elements, and the bones correspond presumably to a single individual. The relative size of the bones suggests a medium−sized individual whose total length was approximately 10 to 12 m. In addition, several vertebral centra and femur fragments from a small ornithopod, two spinosaurid theropod vertebrae and a crocodile tooth were recovered from the site.

Other fossils
Among others, the following fossils have been reported from the Urbión Group:


 * Chitracephalus dumonii - Pinilla de los Moros Formation
 * Larachelus morla - Pinilla de los Moros Formation
 * Europatitan eastwoodi - Castrillo de la Reina Formation
 * Goniopholis sp.
 * Lepidotes sp.
 * Polacanthus sp.
 * Baryonychinae indet.
 * Crocodyliformes indet.
 * Hypsilophodontidae indet.
 * Iguanodontia indet.
 * Rhabdodontidae indet.
 * Testudines indet.


 * ichnofossils
 * Brachyguanodonipus sp.