About 30 million years ago, the Loranca basin in Cuenca was populated by land and marine mammals. They were the ancestors of current species, although relatively little is known about them and whether or not they coexisted with other species. The fossils found so far in this area are only a small sample of the province’s great paleontological heritage.
“The Loranca Basin is very famous in the paleontology of mammals of the Iberian Peninsula because it presents a unique temporal sequence of sites,” explains Cuenca paleontologist Fernando Blanco. There are six sites that can reveal what the region was like over a wide period that covers, the oldest, up to 30 million years ago. The most recent dates back to about six or four million years ago.
During the first two weeks of September, an international group of paleontologists from the University of Gothenburg, CENIEH, the University of Cambridge and the University of Alcalá, among other institutions, will reopen excavations at two of these sites: Cerro Arenoso and Valquemado.
This is a project co-directed by Fernando Blanco, a researcher at the University of Gothenburg, and Ignacio A. Lazagabaster, a researcher at the National Center for Research on Human Evolution (CENIEH). During the campaign, the researchers will work systematically to search for new fossils and contribute to the collection of the Paleontological Museum of Castilla-La Mancha, which has become an ally of the initiative.
The study area is located just over two hours’ drive from another of Cuenca’s largest deposits, Las Hoyas. Of course, in their case we are talking about the Mesozoic era, in the Lower Cretaceous, between 125 and 110 million years ago in a territory dominated, among others, by the dinosaurs that visited the place. “At that time, the Iberian Peninsula was a group of islands and this was no longer the case at the time we are talking about.”
The evolutionary history of Cerro Arenoso and Valquemado has little to do with that of Las Hoyas, but given the good results obtained at this other site, scientists hope to extract a lot of information a little further north, about what happened about 100 million years ago… years later.
At Cerro Arenoso, there was still water even though the environment was already drier. “We have records of turtles and crocodiles. “It seems obvious that there must have been large bodies of water, sufficient to support crocodiles of considerable size.”
Cerro Arenoso, a fortuitous discovery thanks to the transfer works
The Cerro Arenoso paleontological site dates back to about 29 or 30 million years ago. It was discovered in the late 60s of the 20th century during the Tajo-Segura transfer works in the town of Carrascosa del Campo, in Cuenca. It is something common. In 2019, road works in Albacete revealed the existence of more than 6,000 fossils dating back about seven million years.
At that time, excavations were already being carried out that revealed the importance of the place for the study of the Eocene-Oligocene transition. The researchers discovered a mixture of mammal faunas from earlier periods. For example, among the last representatives of a family of artiodactyls similar to suidae, the current pigs, called Dichobunidae.
They also encountered representatives of modern fauna, with species from the family Gelocidaewhich gave rise to ruminants such as deer, bovids including bison and wildebeest and even gave rise to giraffes which are today represented by giraffes and okapis.
The last excavations of the site were carried out in the 90s of the last century. Since then, the site has remained inactive.
Fernando Blanco, a paleontologist specializing in the evolution of ecosystems and especially mammals, believes that Cerro Arenoso can offer evidence of the presence of other species. “We think it is possible to find remains of birds and this would be very important for science because there are still gaps in knowledge about their appearance at that time.” In this regard, he points out that there are “many mentions of birds before the extinction of the dinosaurs and others more modern, but we know little about this stage.”
And the remains of human ancestors?, we ask. “At the moment, we are talking about primates. The human lineage is more recent. Even the Miocene is still a very ancient time for human beings,” explains the researcher who assures that “it would be a bomb to find remains of primates from the Oligocene”, while acknowledging that “in general, paleontology is an improbable science when we talk about fossils, taking into account that of all the diversity on Earth, only a tiny amount fossilizes.
The Early Oligocene is a period that spans between 33.9 and 27.82 million years ago. The dinosaurs had already disappeared and it was a crucial period for the evolution of the terrestrial mammal faunas that we know today. It is also known to have been a transitional time, after a humid climate characterized by tropical forests during the previous era, the Eocene.
“It was an important geological moment in which, for example, the Himalayas and the Alps were formed,” explains the paleontologist. During this transition, permanent polar ice caps were also formed in Antarctica, causing a global cooling that still persists today. This climate change produced radical alterations in ecosystems, causing the extinction of groups of mammals from previous eras and giving way to modern faunas. These are the ones that have evolved into current mammals over millions of years.
Valquemado, a Miocene site
Paleontologists will also study a second site known as Valquemado, located in the municipality of Huete. It dates from the early Miocene, about 23 million years ago, and continues the time sequence that began at Cerro Arenoso.
Here, when we talk about mammals, the available evidence suggests that only one genus (Cainotherium) among those documented in Cerro Arenoso persisted in Valquemado. “Of those that existed, only this one is preserved. The site gives us information about how species replacement occurs temporarily.
In this place, the diversification of artiodactyls (relatives of today’s wild boars, antelopes and giraffes) is observed, which surpass perissodactyls (including horses and rhinoceroses) in abundance and diversity, reversing the trend of the previous era and which continues to this day. As for the birds of the Miocene, experts have more evidence. “They are very similar to the current ones.”
At this time, we are talking about primates. The human lineage is more recent. Even the Miocene is still a very ancient time for human beings. It would be a bombshell to find primate remains from the Oligocene.
Using computational paleontology, specialists are looking for evolutionary models. For example, “to determine when certain extinction peaks occurred.” The two sites are “key” in a very large macro-evolutionary puzzle throughout the Iberian Peninsula, but they will serve in particular to understand the diversity of mammals that we have today and, incidentally, assures Fernando Blanco, “this will help us to understand their current state and how they will evolve in the future.”
It is also hoped that this will dispel some doubts about the period. “We have very few examples in the world of the Oligocene. We can cite the Quercy site in France where we also find a sequence of sites from the period,” says Fernando Blanco. “The Loranca basin is at this level and will provide us with invaluable information on environmental change at the time, how it affected the species that populated the Iberian Peninsula and how the transition of fauna and vegetation took place.”
The informative objective of the project with lectures and guided tours
This project combines scientific purpose and dissemination to the local population. “The rich paleontological heritage of the region not only has an inestimable cultural value, but can also stimulate the local economy. We hope that the deposit and the future project of the Loranca basin will have an economic impact on the region,” says Lazagabaster.
The Museo de Paleontología de Castilla-La Mancha, based in Cuenca, has been involved in the idea and, thanks to the support of the MICE 2024 programme of the Junta de Castilla-La Mancha, will organise a series of conferences on paleontology and evolution for the general public during the first half of September.
The conferences will take place at 7:30 p.m. at the El Silo cultural center in Carrascosa del Campo. The first one will take place on September 3. It will be led by Mercedes Llandres, curator of the Museum of Paleontology, who will talk about the Present and future of the Cuenca deposits.
On September 5, Ignacio A. Lazagabaster will give the conference Digging into our ancestors: from Africa to the Iberian Peninsula. Already on September 10, Guillermo Navalón, from the University of Cambridge, will speak about Dinosaurs that survived: from Brazil to the Iberian Peninsula and on September 12, Juan L. Cantalapiedra of the National Museum of Natural Sciences will explain Why we look for fossils.
