The La Huérguina Formation (also known as the Calizas de La Huérguina Formation, La Huérguina Limestone Formation or as the Una Formation) is a geological formation in Spain whose strata date back to the Barremian stage of the Early Cretaceous.Martínez et al., 2017 Las Hoyas is a Konservat-Lagerstätte within the formation, located near the city of Cuenca, Spain. The site is mostly known for its exquisitely preserved dinosaurs, especially enantiornithines.Weishampel et al., 2004, pp.556-563 The lithology of the formation mostly consists of lacustrine limestone deposited in a freshwater wetland environment.

Las Hoyas

Taphonomy

As a Konservat-Lagerstätte, 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, Weichselia or Frenelopsis) and diverse fauna, with specimens of at least five or six phyla: arthropods, molluscs, chordates 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. The date of the Las Hoyas age is constrained to Late Barremian by charophyte and ostracod assemblages.

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.

Fossil content

Crustaceans Crustaceans Genus Species Location Stratigraphic position Material Notes Images Austropotamobius A. llopisi Las HoyasNumerous specimens A crayfishDelclosiaD. martinelliAn atyid shrimpLahuerguinagrapta L. multicostata A clam shrimp belonging to the family AfrograptidaeSkyestheriaIndeterminateA clam shrimp belonging to the family Polygraptidae PseudestheritesA clam shrimp belonging to the family Antronestheriidae Spinogriphus S. ibericus A member of Peracarida belonging to Spelaeogriphacea

Chondrichthyes Chondrichthyes Genus Species Location Stratigraphic position Material Notes Images Lonchidion Indeterminate Las Hoyas A full body impression of a juvenile Hybodont

Osteichthyes Osteichthyes Genus Species Location Stratigraphic position Material Notes ImagesCaturus Caturus sp. Las Hoyas AmiiformesGordichthys G. conquensis Las Hoyas GonorynchiformHispanamia H. newbreyi Las Hoyas Amiid, originally described as Amiopsiscf. "Holophagus" Indeterminate Las Hoyas Coelacanth, probably does not belong in Holophagus proper.Hoyasotes H. tanyrhis Las Hoyas Member of Lepidotidae, originally described as Lepidotes Lepidohyas L. microrhis Las Hoyas Notagogus N. aff. N. ferreri Las Hoyas Macrosemiid Pleuropholis P. sp. Las Hoyas Propterus P. sp. Las HoyasMacrosemiid Rubiesichthys R. gregalis Las Hoyas Gonorynchiform Stenamara S. mia Las Hoyas Pycnodont Turbomesodon T. praeclarus Las Hoyas Vidalamia V. cf. catalunica Las Hoyas Amiid

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 eucryptodirePérez García et al., 2012 Pleurosternidae Indeterminate Uña Pelomedusidae Indeterminate Uña

Squamates Squamates Genus Species Location Stratigraphic position Material Notes Images Becklesius Indeterminate, B. cataphractus Uña Paramacellodid lizard Cuencasaurus C. estesi Uña Hoyalacerta H. sanzi Las Hoyas Jucaraseps J. grandipes Las Hoyas Scleroglossa Meyasaurus M. diazromerali Las Hoyas Teiioid lizard M. unaensis Uña Paramacellodus P. sinuosus Uña Paramacellodid lizard Scandensia S. ciervensis Las Hoyas

Mammals Mammals Genus Species Location Stratigraphic position Material Notes Images Crusafontia C. cuencana Uña Dryolestid Eobaatar E. hispanicus Uña Eobaatarid multituberculate Galveodon G. nannothus Uña Paulchoffatiid multituberculate SpinolestesMartin et al., 2015 S. xenarthrosus Las Hoyas Exceptionally complete specimen, preserving soft tissues such as pelage, ears and internal organs. Gobiconodont eutriconodont

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." Carcharodontosaur dinosaurOrtega et al., 2010 Concornis"15.9 Provincia de Quenca, Spain; 4. Calizas de La Huergina Formation," in Weishampel et al., 2004, pp.561-562 C. lacustris Las Hoyas "Postcranial skeleton.""Table 11.1," in Weishampel et al. , 2004, p.212Enantiornithean bird Eoalulavis E. hoyasi Las Hoyas "Thoracic region and forelimbs." Enantiornithean bird EuronychodonListed as "cf. Euronychodon sp." in "15.9 Provincia de Quenca, Spain; 4. Calizas de La Huergina Formation," in Weishampel et al., 2004, p.561 Indeterminate Las Hoyas Theropod dinosaur Europejara E. olcadesorum Las Hoyas Tapejarid pterosaur GorgonavisG. alcyoneLas Hoyas Partial skull Enantiornithean bird Iberomesornis I. romerali Las Hoyas Postcranial skeleton Enantiornithean bird"Table 11.1," in Weishampel et al., 2004, p.213 Mantellisaurus M. atherfieldensis Las Hoyas "incomplete but fully-articulated right hindlimb" Iguanodontian dinosaurSerrano et al., 2013 Pelecanimimus P. polyodon Las Hoyas "Skull and partial skeleton" Ornithomimosaurian dinosaur"Table 6.1," in Weishampel et al., 2004, p.138 ParonychodonListed as "cf. Paranychodon sp." in "15.9 Provincia de Quenca, Spain; 4. Calizas de La Huergina Formation," in Weishampel et al., 2004, p.561 Indeterminate Las Hoyas Theropod dinosaur Richardoestesia Listed as "cf. Ricardoestesia sp." in "15.9 Provincia de Quenca, Spain; 4. Calizas de La Huergina Formation," in Weishampel et al., 2004, p.561 Indeterminate Las Hoyas Theropod dinosaur

Correlation

See also List of dinosaur-bearing rock formations Paja Formation, contemporaneous Lagerstätte of Colombia Yixian Formation, contemporaneous Lagerstätte of China

References

Bibliography

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

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. (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.

External links Las Hoyas site website