Taphonomy

As a Konservat-Lagerstätten, the preservation is exceptional. This may be a result of three factors: Microbial mats, Obruption and Stagnation.

Microbial mats may be responsible for the preservation of soft tissue in many fossils from Las Hoyas, like Pelecanimimus' crest. The iron carbonate depositions, a result from bacterial metabolism which covered the dinosaur's crest enhanced the preservation of those soft tissues. Evidence of these mats comes from the studies on microfacies and the fossils themselves.

Obruption is notable in the formation, due to the presence of highly articulated specimens. From actuotaphonomy studies on several different organisms it can be estimated that the burial of most entities was quick. Concornis may have been buried in less than 15 days, after a period of sub-areal exposition.

Paleoenvironment

Las Hoyas was an inland lacustrine environment which presents an important aquatic and terrestrial flora (with many specimens of Charophytes, Montsechia, Weischelia or Frenelopsis) and diverse fauna, with specimens of at least five or six Phyla: arthropods, molluscs, Chordata and many vermiform soft bodied animals which might be Nemertines or annelids.

Among vertebrates the most abundant and diverse group are fish. The presence of mostly articulated skeletons, exceptional preservation of tissue and lack of any other signs of transportation may indicate that these are demic and autochthonous entities (meaning that they lived and died in the same place where they fossilized).

Crocodylomorphs are the most abundant amniotes from Las Hoyas.

Dinosaurs from Las Hoyas (avian and non avian) are unique in many ways. The first ornithomimosaur dinosaur described in Europe, Pelecanimimus polyodon, shows some characters previously unknown in these dinosaurs which enhanced the knowledge on the evolution of the group, such as a high number of teeth. Concavenator corcovatus presents two unique features: very tall neural spines on the vertebrae near the hip, which look like a hump, and a structure on its forearm, which if homologous to quill knobs would push back the origin of feathers earlier in theropod evolution.

Las Hoyas birds are enantiornithes, the most diverse Cretaceous bird clade, which became extinct at the end of the period. Iberomesornis romerali shows both derived ("avian") and primitive ("dinosaurian") characters. Within the derived characters we can underline the presence of a pygostile, although it is still very large compared to that of modern neornithines and the presence of a quilled sternum. Eoalulavis hoyasi shows the first report of an alula or "bastard wing", which means it had a flight manoeuvrability analogous to that of modern birds.

Research

The Las Hoyas site has been studied for more than two decades by researchers from the Universidad Autónoma de Madrid, the Universidad Complutense de Madrid and the National University of Distance Education, in collaboration with the Museo de las Ciencias de Castilla-La Mancha, which is responsible for the fossil record from the area.

Crustaceans

Chondrichthyes

Osteichthyes

Amphibians

Amphibians
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Albanerpeton	Indeterminate	Uña		Frontals	Albanerpetontid
Celtedens	C. ibericus	Las Hoyas
	C. megacephalus	Uña
Gracilibatrachus	G. avallei	Las Hoyas			Pipimorph frog
Hylaeobatrachus	Indeterminate	Las Hoyas			Salamander
Iberobatrachus	I. angelae	Las Hoyas			Frog
Valdotriton	V. gracilis	Las Hoyas			Salamander
Wealdenbatrachus	W. jucarensis	Uña			Frog

Turtles

Turtles
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Hoyasemys	H. jimenezi	Las Hoyas			A eucryptodire[10]
Pleurosternidae	Indeterminate	Uña
Pelomedusidae	Indeterminate	Uña

Squamates

Mammals

Crocodyliformes

Crocodyliformes
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Bernissartia	Indeterminate	Uña
Cassissuchus	C. sanziuami	Las Hoyas			Gobiosuchid
Montsecosuchus	Indeterminate	Las Hoyas
Sabresuchus	S.ibericus	Uña
Unasuchus	U. reginae	Uña
Bernissartiidae	Indeterminate	Las Hoyas

Ornithodirans

Ornithodirans
Genus	Species	Location	Stratigraphic position	Material	Notes	Images
Concavenator	C. corcovatus	Las Hoyas		"Nearly complete and articulated skeleton."	Carcharodontosaurid dinosaur[12]
Concornis[13]	C. lacustris[13]	Las Hoyas		"Postcranial skeleton."[14]	enantiornithean bird
Eoalulavis[13]	E. hoyasi[13]	Las Hoyas		"Thoracic region and forelimbs."[14]	enantiornithean bird
Euronychodon	Indeterminate	Las Hoyas			[15]
Europejara	E. olcadesorum	Las Hoyas			Tapejarid pterosaur
Iberomesornis	I. romerali	Las Hoyas		"Postcranial skeleton."	enantiornithean bird[13][16]
Mantellisaurus	M. atherfieldensis	Las Hoyas		"incomplete but fully-articulated right hindlimb"	Iguanodontian dinosaur[17]
Pelecanimimus	P. polyodon	Las Hoyas		"Skull and partial skeleton"	Ornithomimosaurian dinosaur[13][18]
Paronychodon	Indeterminate	Las Hoyas			[19]
Ricardoestesia	Indeterminate	Las Hoyas			[20]

Bibliography

• Martínez, Marian Fregenal; Nieves Meléndez; M. Belén Muñoz García; Javier Elez, and Raúl de la Horra. 2017. The stratigraphic record of the Late Jurassic-Early Cretaceous rifting in the Alto Tajo-Serranía de Cuenca region (Iberian Ranges, Spain): genetic and structural evidences for a revision and a new lithostratigraphic proposal. Revista de la Sociedad Geológica de España 30. 113–142. Accessed 2019-10-12.
• Serrano, Mercedes Llandres; Romain Vullo; Jesús Marugán-Lobón; Francisco Ortega, and Ángela D. Buscalioni. 2013. An articulated hindlimb of a basal iguanodont (Dinosauria, Ornithopoda) from the Early Cretaceous Las Hoyas Lagerstätte (Spain). Geological Magazine 150(3). 572–576. Accessed 2019-10-12. doi:10.1017/S0016756813000095 ISSN 0016-7568
• Pérez García, Adán; Marcelo S. de la Fuente, and Francisco Ortega. 2012. A New Freshwater Basal Eucryptodiran Turtle from the Early Cretaceous of Spain. Acta Palaeontologica Polonica 57(2). 285–298. Accessed 2019-10-12. doi:10.4202/app.2011.0031 ISSN 0567-7920
• Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad, Zhe-Xi Luo & Angela D. Buscalioni (2015). A Cretaceous eutriconodont and integument evolution in early mammals. Nature 526, 380–384. doi:10.1038/nature14905
• Ortega, F., Escaso, F. & Sanz, J. L. (2010): A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain Nature 467: 203-206. HTML abstract
• Weishampel, David B.; Peter Dodson, and Halszka Osmólska (eds.). 2004. The Dinosauria, 2nd edition, 1–880. Berkeley: University of California Press. Accessed 2019-02-21. ISBN 0-520-24209-2
• Sanz, José L.; Chiappe, Luis M.; Pérez Moreno, Bernardino P.; Buscalioni, Ángela D.; Moratalla, José J.; Ortega, Francisco & Poyato Ariza, Francisco J. (1996): An Early Cretaceous bird from Spain and its implications for the evolution of avian flight. Nature 382(6590): 442-445. doi:10.1038/382442a0 (HTML abstract)
• Pérez Moreno, B. P., Sanz, J. L., Buscalioni, A. D., Moratalla, J. J., Ortega, F., and Raskin-Gutman, D. (1994). "A unique multitoothed ornithomimosaur from the Lower Cretaceous of Spain." Nature, 30: 363-367.
• Sanz, J. L. & Bonaparte, José F. (1992): A New Order of Birds (Class Aves) from the Lower Cretaceous of Spain. In: Jonathan J. Becker (ed.): Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Contributions in Science 36: 38-49.
• Sanz, J. L. & Buscalioni, A.D. (1992): A new bird from the Early Cretaceous of Las Hoyas, Spain, and the early radiation of birds. Palaeontology 35(4): 829-845. PDF fulltext