# La Huérguina Formation

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. 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. The lithology of the formation mostly consists of lacustrine limestone deposited in a freshwater wetland environment.

## Las Hoyas
### 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.

## Fossil content

| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |

### Crustaceans

Crustaceans :
| Genus | Species | Location | Material | Notes |
| Austropotamobius | A. llopisi | Las Hoyas | Numerous specimens | A crayfish |
| Delclosia | D. martinelli | Las Hoyas | Numerous specimens | An atyid shrimp |
| Lahuerguinagrapta | L. multicostata | Las Hoyas | | A clam shrimp belonging to the family Afrograptidae |
| Skyestheria | Indeterminate | Las Hoyas | | A clam shrimp belonging to the family Polygraptidae |
| Pseudestherites | Indeterminate | Las Hoyas | | A clam shrimp belonging to the family Antronestheriidae |
| Spinogriphus | S. ibericus | Las Hoyas | | 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 | Notes |
| Caturus | Caturus sp. | Las Hoyas | Amiiformes |
| Gordichthys | G. conquensis | Las Hoyas | Gonorynchiform |
| Hispanamia | H. newbreyi | Las Hoyas | Amiid, originally described as Amiopsis |
| cf. "Holophagus" | Indeterminate | Las Hoyas | Coelacanth |
| Hoyasotes | H. tanyrhis | Las Hoyas | Member of Lepidotidae, originally described as Lepidotes |
| Lepidohyas | L. microrhis | Las Hoyas | Member of Lepidotidae, originally described as Lepidotes |
| Notagogus | N. aff. N. ferreri | Las Hoyas | Macrosemiid |
| Pleuropholis | P. sp. | Las Hoyas | |
| Propterus | P. sp. | Las Hoyas | Macrosemiid |
| Rubiesichthys | R. gregalis | Las Hoyas | Gonorynchiform |
| Stenamara | S. mia | Las Hoyas | Pycnodont |
| Turbomesodon | T. praeclarus | Las Hoyas | Pycnodont |
| Vidalamia | V. cf. catalunica | Las Hoyas | Amiid |

### Amphibians

Amphibians :
| Genus | Species | Location | Material | Notes |
| Albanerpeton | Indeterminate | Uña | Frontals | Albanerpetontid |
| Celtedens | C. ibericus | Las Hoyas | | Albanerpetontid |
| Celtedens | C. megacephalus | Uña | | Albanerpetontid |
| 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 | Notes |
| Hoyasemys | H. jimenezi | Las Hoyas | A eucryptodire |
| Pleurosternidae | Indeterminate | Uña | |
| Pelomedusidae | Indeterminate | Uña | |

### Squamates

Squamates :
| Genus | Species | Location | Notes |
| 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 |
| Meyasaurus | M. unaensis | Uña | teiioid lizard |
| Paramacellodus | P. sinuosus | Uña | Paramacellodid lizard |
| Scandensia | S. ciervensis | Las Hoyas | |

### Mammals

Mammals :
| Genus | Species | Location | Material | Notes |
| Crusafontia | C. cuencana | Uña | | Dryolestid |
| Eobaatar | E. hispanicus | Uña | | Eobaatarid multituberculate |
| Galveodon | G. nannothus | Uña | | Paulchoffatiid multituberculate |
| Spinolestes | S. xenarthrosus | Las Hoyas | Exceptionally complete specimen, preserving soft tissues such as pelage, ears and internal organs. | Gobiconodont Eutriconodont |

### Crocodyliformes

Crocodyliformes :
| Genus | Species | Location | Notes |
| 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 | Material | Notes |
| Concavenator | C. corcovatus | Las Hoyas | "Nearly complete and articulated skeleton." | Carcharodontosaurid dinosaur |
| Concornis | C. lacustris | Las Hoyas | "Postcranial skeleton." | enantiornithean bird |
| Eoalulavis | E. hoyasi | Las Hoyas | "Thoracic region and forelimbs." | enantiornithean bird |
| Euronychodon | Indeterminate | Las Hoyas | | |
| Europejara | E. olcadesorum | Las Hoyas | | Tapejarid pterosaur |
| Iberomesornis | I. romerali | Las Hoyas | "Postcranial skeleton." | enantiornithean bird |
| Mantellisaurus | M. atherfieldensis | Las Hoyas | "incomplete but fully-articulated right hindlimb" | Iguanodontian dinosaur |
| Pelecanimimus | P. polyodon | Las Hoyas | "Skull and partial skeleton" | Ornithomimosaurian dinosaur |
| Paronychodon | Indeterminate | Las Hoyas | | |
| Ricardoestesia | Indeterminate | Las Hoyas | | |

## Correlation

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