Location: Cuenca, Spain
Age: Barremian (Lower Cretaceous)
The Las Hoyas Lagerstatte has yielded a rich terrestrial and freshwater assemblage. Fossils include invertebrate and vertebrate trace fossils, early angiosperms, ferns, cycads, conifers, insects, birds, fish, crocodiles, a dinosaur, amphibians and lizards. Over 200 complete specimens of terrestrial vertebrates have been found.
The study of the Las Hoyas invertebrate ichnofauna represents one of the first detailed studies of carbonate lacustrine trace fossils.
The assemblage has low ichnodiversity, and shallow burrows evident in the sediments are produced mainly by detritus feeders. This indicates a low to moderately low energy palaeoenvironment. There is no evidence of desiccation so it was therefore permanently submerged. The low ichnodiversity and shallow burrows show environmental stress. This has been interpreted as a result of low oxygen conditions in interstitial waters. Improved oxygen conditions can be observed in event beds where there is opportunistic colonisation by epifauna and shallow infauna. These occurred due to density underflows and dilute turbidity currents. These currents have implications for the preservation of other fossils in the Las Hoyas assemblage because they allow rapid burial of newly killed organisms.
The Las Hoyas invertebrate ichnofauna is similar to other shallow lacustrine trace-fossil assemblages such as the archetypal Scoyenia ichnofacies.
Vertebrate trace fossils include those of crocodiles and turtles. Crocodilian trackways on an emergent surface show the animals walked with a very regular step and stride length. The turtle ichnofauna are more isolated but show a striking similarity between those of the Late Jurassic tracks at Cerin, in France. This suggests the ichnofaunas are similar.
Most of the specimens are very small, but are nevertheless recognisable as leaf fragments. The leaves are fossilised as imprints on the platy limestone. The preservation is good, and epidermal detail has been obtained from several examples. Some delicate remains are unusually preserved indicating a limited residence time in water before preservation. Sedimentological and taphonomic analysis show that these assemblages were deposited in the lacustrine setting through fluvial transport. Las Hoyas land-plant palaeobiodiversity was high with many species identified.
Ten taxa of ferns are observed in the Las Hoyas assemblage are attributed to the families Matoniaceae, Dicksoniaceae and Schizaeaceae, whilst eight are unclassified. This assemblage is similar to the Wealden facies of England and is the same age (115Ma).
The Las Hoyas lizard fossils are represented by three taxa including the first complete examples of Meyasaurus. This has allowed a detailed morphological description as well as comprehensive phylogenetic analysis. Meyasaurus has also been described from other Spanish localities of the same age.
A short-limbed relation of Meyasaurus has also been found. Comparison with other Jurassic and Early Cretaceous lizards supports the decision to create a new taxon for this specimen. It is called Hoyalacerta. A climbing lizard found in the Las Hoyas assemblage is also distinct enough to form a new genus: Scandensia. The salamander Valdotriton is also found in the Las Hoyas assemblage. It is important because it an internally fertilizing salamander.
Las Hoyas is one of the best sites for fossil birds in the world. Three types of birds are among the most important finds at Las Hoyas. Iberomesornis is one of the most important birds found in the Las Hoyas assemblage. It is roughly sparrow sized and shows feathers capable of allowing full flight, but it still keeps some primitive characters more similar to Archaeopteryx. It shows how much birds evolved from the Jurassic (Archaeopteryx, 150Ma) to the Barremian (Early Cretaceous, 121-127Ma).
Concornis, also found at Las Hoyas, is roughly twice the size of Iberomesornis showing that these (still fairly early) birds could achieve relatively large sizes. It also adds to the evidence that there was ever increasing avian adaptive radiation in the Early Cretaceous. Due to their long leg length, these Las Hoyas birds were probably aquatic. This is perhaps why they are preserved so well.
Eoalulavis has also been found at Las Hoyas. It had an alula or bastard wing. This is common with many extant birds, but had previously not been found on any Mesozoic specimens. It was important because it showed Barremian birds could fly and manoeuvre as well almost as well as modern birds.
Nonavian dinosaur material at Las Hoyas is scarce, but nonetheless present. Isolated theropod teeth have been found, along with fragmentary sauropod vertebrae. Some of the lateral detrital facies have yielded Iguanodon bones.
The most important find has been that of Pelecanimimus, which literally means pelican mimic with many teeth. It had 220 teeth, making it the toothiest of all tetrapods. This is even more important when it is noted that all its closest relatives had toothless beaks. Pelecanimimus and other toothed ornithomimids may therefore represent the primitive condition of ornithomimosaurs. The fossil included the mineralised soft tissue of the animal making it particularly interesting. Its skin was preserved and incredibly it was smooth, with no dermal structures like feathers (e.g. Archaeopteryx), scutes or osteoderms (e.g. tyrannosaurs and stegosaurs). This is unique to the Dinosauria.
The first dinosaur vomit is also thought to have been found
at Las Hoyas. The fossilised pellet contains remains from four
birds of three distinct species. The polytypic nature of this
fossil is uncharacteristic of Las Hoyas fossils, leading to the
conclusion that the different species must have been brought together
as prey items. It is thought not to be a coprolite as the bones
are not crushed up enough. There is, however, evidence of acid
damage on the bird bones showing they had come into contact with
stomach acid. However, the acid damage is not bad enough for the
bones to have passed through the entire digestive system of the
predator that ate them. It is therefore thought to be a regurgitative
pellet. Small carnivorous dinosaurs are thought to be the animal
that produced the pellet, but it is unlikely that conclusive evidence
will be found.
Proceed to section 4: Taphonomy
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