This study describes the first bacterial infection of cutaneous origin in a dinosaur that lived in Morella about 125 million years ago

The Lower Cretaceous sediments that outcrop in the surroundings of Morella (Castellón) continue to offer exceptional findings regarding the life of European dinosaurs some 125 million years ago. On this occasion, a team of researchers from the UNED has identified in a fossil attributed to Iguanodon bernissartensis the first documented evidence of a bone reaction caused by a bacterial infection originating from a skin ulcer. The work, published in the journal Royal Society Open Science, constitutes a significant advance in the knowledge of the diseases that affected dinosaurs and how their organisms responded to serious infections.

Although the fossil record preserves thousands of dinosaur bones, it is very rare for them to allow for the reconstruction of aspects of a specific individual's health. Fossil pathologies offer a unique opportunity to understand how these animals became ill, how their tissues reacted, and to what extent they could survive potentially incapacitating injuries. In recent decades, paleopathology has acquired an increasingly important role in interpreting the biology, behavior, and evolution of extinct vertebrates.

A dinosaur with a serious leg infection

The fossil studied corresponds to a right tibia more than one meter in length belonging to one of the most iconic groups of herbivorous dinosaurs of the European Lower Cretaceous and which, in this case, has been attributed to Iguanodon bernissartensis. The fossil comes from the Mas de la Parreta site (Morella), located in the Arcillas de Morella Formation, and was discovered during the paleontological monitoring of clay extraction work carried out by the company Arcillas Vega del

Moll. The collaboration between mining activity and paleontological research has allowed for the recovery of numerous partial skeletons of various dinosaurs over the last few decades, helping to consolidate Morella as one of the European benchmarks for the study of Lower Cretaceous ecosystems.

To the naked eye, the bone presents an anomalous bulge in the middle part of the tibia. The surface is smooth and thickened, with no obvious signs of fractures or significant deformations. However, the appearance of the lesion was not enough to establish its origin, and it was necessary to resort to a differential diagnosis that would allow for the exclusion of different pathologies before reaching a conclusion.

Standard radiological techniques used in hospital medicine were employed. The tibia was studied using computed tomography (CT) at the Hospital General Universitario de Castellón, obtaining high-resolution three-dimensional images that allowed the interior of the bone to be observed without damaging it. Subsequently, three-dimensional digital reconstructions were generated to analyze the structure of the lesion in detail.

The images obtained allowed for an exhaustive differential diagnosis. The researchers ruled out that the thickening corresponded to a fracture callus, as the bone did not show the internal alterations characteristic of a bone remodeling process observed during the healing of a fracture. Various diseases of tumoral origin were also rejected, given that the lesion lacked the diagnostic features typical of these pathologies.

The most consistent explanation was that the bone had reacted to a soft tissue infection located over the tibia. The dinosaur's organism responded by forming new bone tissue around the affected area, producing a periosteal reaction and a thickening of the bone cortex. According to the authors, the characteristics of the lesion are compatible with an advanced cutaneous ulcer of bacterial origin, probably polymicrobial, similar to those known as tropical ulcers described in human medicine. This is the first time that this type of pathological response has been documented in a dinosaur.

A window into dinosaur health

The study demonstrates that the animal did not die immediately after suffering the infection. The formation of new bone tissue indicates that it survived long enough for its organism to develop a prolonged inflammatory response and begin the healing process. The researchers believe that the lesion must have caused persistent pain, inflammation, and significant functional limitation in the limb, likely altering its way of walking.

In addition to expanding knowledge about the diseases that affected dinosaurs, the work shows how imaging techniques commonly used in modern medicine allow us to investigate the health of animals that went extinct millions of years ago. The combination of computed tomography, three-dimensional reconstructions, and differential diagnosis has provided a level of detail that was unthinkable in paleontology just a few decades ago.

Morella, a natural laboratory of the Cretaceous

This new discovery reinforces the extraordinary scientific value of the sites in the Arcillas de Morella Formation. Since the first dinosaur remains were identified in the region in the 19th century, excavations have provided some of the most important fossil assemblages of the European Lower Cretaceous. Among them, several species described for the first time in this region stand out, such as the herbivorous dinosaurs Morelladon beltrani and Garumbatitan morellensis in Morella, or the carnivorous dinosaurs Vallibonavenatrix cani, from Vallibona, and Protathlitis cinctorrensis, from Cinctorres. Along with these exclusive species, the Arcillas de Morella Formation has provided abundant remains of other dinosaurs widely distributed throughout Europe, among which the large ornithopod Iguanodon bernissartensis stands out. This study allows us to delve not only into the anatomy and evolution of this species, but also into much less known aspects of its biology, such as the diseases they suffered and how they responded to them.

The research was carried out by researchers from the Universidad Nacional de Educación a Distancia (UNED), in collaboration with specialists from the Hospital General Universitario de Castellón, where the studies were conducted using computed tomography that allowed for the reconstruction of the clinical history of this dinosaur from over 120 million years ago.