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.

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.

The fossil bones of Demandasaurus were recovered in the "Tenadas de los Vallejos II" quarry, located 10 kilometres (6.2 mi) 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 square metres (2,600 sq ft). 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 metres (33 to 39 ft). 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.

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

Early Cretaceous stratigraphy of Iberia

Ma	Age	Paleomap \ Basins	Cantabrian	Olanyà	Cameros	Maestrazgo	Oliete	Galve	Morella	South Iberian	Pre-betic	Lusitanian
100	Cenomanian		La Cabana	Sopeira	Utrillas		Mosquerela					Caranguejeira
			Altamira		Utrillas
			Eguino
125	Albian		Ullaga - Balmaseda	Lluçà						Traiguera
			Monte Grande		Escucha		Escucha			Jijona
			Itxina - Miono
	Aptian		Valmaseda - Tellamendi		Ol Gp. - Castrillo	Benassal		Benassal				Olhos
				Font	En Gp. - Leza	Morella/Oliete	Oliete	Villaroya	Morella	Capas Rojas		Almargem
			Patrocinio - Ernaga	Senyús	En Gp. - Jubela	Forcall				Villaroya	Upper Bedoulian	Figueira
	Barremian		Vega de Pas	Cabó	Abejar	Xert	Alacón	Xert		Huérguina		Assises
				Prada		Artoles				Collado	Moutonianum	Papo Seco
				Rúbies	Tera Gp. - Golmayo	Alacón/Blesa	Blesa	Camarillas	Mirambel
150	Hauterivian				Ur Gp. - Pinilla	Llacova		Castellar	Tera Gp. - Pinilla	Villares		Porto da Calada
							hiatus
						Huerva			Gaita
	Valanginian		Villaro		Ur Gp. - Larriba				Ped Gp. - Hortigüela
					Ped Gp. - Hortigüela				Ped Gp. - Piedrahita
					Peñacoba			Galve		Miravetes
	Berriasian		Cab Gp. - Arcera		Valdeprado	hiatus		Alfambra
					TdL Gp. - Rupelo			Arzobispo	hiatus	Tollo
					On Gp. - Huérteles Sierra Matute
	Tithonian		Lastres		Tera Gp. - Magaña		Higuereles			Tera Gp. - Magaña		Lourinhã
									Arzobispo
					Ágreda
Legend		Major fossiliferous, oofossiliferous, ichnofossiliferous, coproliferous, minor formation
Sources

• List of dinosaur-bearing rock formations

• Melero Rubio, M.; Pérez Lorente, F. (2011). "Huellas en las obras. Reconocimiento y estudio de huellas fósiles de dinosaurio en las obras de la presa de Enciso (La Rioja. España) - Footprints in the works. Recognition and study of fossil dinosaur footprints in the works of the Enciso dam (La Rioja. Spain)". Zubía. 29: 31–60. Retrieved 2019-10-12.
• Torcida Fernández-Baldor, F.; Canudo, J.I.; Huerta, P.; Montero, D.; Pereda Suberbiola, X.; Salgado, L. (2011). "Demandasaurus darwini, a new rebbachisaurid sauropod from the Early Cretaceous of the Iberian Peninsula". Acta Palaeontologica Polonica. 56 (3): 535–552. doi:10.4202/app.2010.0003. Retrieved 2019-10-09. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka, eds. (2004). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 1–880. ISBN 0-520-24209-2. Retrieved 2019-02-21.

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