Researchers used ultraviolet radiation to examine the remains of a crocodylomorph dating back 125 million years, revealing striking features such as chest cartilage, sensory receptors and skin textures. The find, recorded in Spanish territory, gives scientists a completely new perspective on the biology of these ancient reptiles. The detailed study on Montsecosuchus depereti was published in the scientific journal Zoological Journal of the Linnean Society on June 13, 2026.
Discovered more than a hundred years ago in the northeastern region of Spain, this small predator from the Early Cretaceous began to display features that went unnoticed by the naked eye. Thanks to the use of special lighting, the scientific team was able to map incredibly intact skin fragments, as well as chest structures and possible original pigmentations. Such evidence provides a valuable overview of the biology and visual appearance of this extinct creature, filling in gaps about the early development of crocodylomorphs.
The role of fluorescence in discovering hidden anatomical structures
The advance occurred by chance, while paleontologists Jesús Serrano and Oscar Castillo organized a digital catalog of pieces housed in European institutions. By applying beams of ultraviolet light to the holotype, they noticed that the fossilized organic material emitted a different fluorescence than the matrix rock. This non-destructive technique highlighted contours impossible to see under conventional lighting, visually separating the bone from the petrified soft matter.
The study’s main researcher, Oscar Castillo-Visa, highlighted that the application of this light frequency allows us to see minutiae that would otherwise be forever hidden in the stone. Using this approach, experts documented various tissues, with emphasis on the scales of the epidermis, marking the first detailed assessment of the species’ body covering since it was described at the beginning of the last century.
The data collected indicates a great diversity in the shape and size of the scales throughout the animal’s body. Furthermore, the analysis proved that the predator did not display the long, flat tail typical of today’s crocodiles, altering the perception that science had about the locomotion and hydrodynamics of these animals in the remote past.
Evolution of the respiratory system and mapping of sensory organs
The light scanning also showed cartilaginous tissue in the chest region, suggesting that the specimen already had a sophisticated respiratory apparatus. This detail proves that certain basal lineages developed a complex rib cage in the early stages of their evolutionary history. Evaluating this scenario, Castillo-Visa points out that such attributes demonstrate a high capacity for adaptation to a semiaquatic life routine, even though it is a primitive organism.
The team of scientists also detected marks that indicate the presence of sensory receptors on the scales, notably on the tail, sides, paws and neck. In modern species, these tiny organs serve to capture chemical stimuli, temperature changes, physical touches and fluctuations in aquatic pressure, facilitating hunting in murky waters.
As these sensors appear only in isolated points in the Catalan fossil, the researchers deduce that the characteristic evolved gradually over the millennia. The evolutionary process likely began in specific zones before covering the entire body of later lineages, showing a fundamental intermediate step in the sensory adaptation of large aquatic reptiles.
Camouflage Patterns and the Earliest Pigmentation Record
One of the most fascinating points of the survey is the discovery of preserved pigmentation on the rear end of the fossil. Under the special radiation, light and dark stripes appeared interspersed on the caudal scales, which the team interprets as the animal’s authentic chromatic pattern. If the hypothesis is confirmed after new tests, it will be the oldest color record ever documented in a relative of the crocodilian lineage.
This type of marking possibly served as pattern-breaking camouflage, helping to hide the predator’s silhouette in the hunting environment among the foliage and water. Albert G. Sellés, who also wrote the research, clarifies that it is not possible to pinpoint the exact tone of the tail, but it is logical to assume that the colors would not differ too much from the pattern seen in contemporary species, which use similar visual strategies for survival.
The geological importance and legacy of the Pedrera de Meià site
Around 125 million years ago, the small reptile perished in a karst lake, located near the coast of what we today call the Catalan Pre-Pyrenees. The carcass sank in an extremely fine mud that gave rise to the lithographic limestones of Pedrera de Meià, an area that today forms part of the Global Origins Geopark, certified by UNESCO. The almost total absence of oxygen at the bottom of this lake prevented the proliferation of decomposing bacteria, creating the perfect chemical environment for delicate tissues to be fossilized along with the bones.
The location bears the title of Konservat-Lagerstätte, an international classification given to very rare fossil deposits capable of immortalizing soft parts with very high fidelity. Thanks to the abundance of materials deposited there, the area has established itself as a primary source for investigating the flora and fauna of the European Lower Cretaceous period.
To date, excavators have removed more than eight thousand pieces from the site, revealing a rich and diverse ecosystem. Among the main finds that shared the habitat with the crocodylomorph, the following groups stand out:
- Land and flying invertebrates in impeccable condition, such as spiders, flies, wasps and beetles.
- Aquatic and semiaquatic animals that formed the base of the food chain, including crustaceans, fish, and primitive amphibians.
- A unique botanical collection that includes Montsechia, considered by the scientific community to be the oldest flowering plant ever cataloged in the world.
The general public has the opportunity to observe a large part of this collection at the Montsec de Meià Interpretation Center, located in the city of Vilanova de Meià. The exhibition complex is part of the Dinosaurs of the Pyrenees circuit, a joint effort between visitor centers and museums to popularize the fossil wealth hidden in the Catalan mountains and promote scientific tourism in the region.
The execution of the project received financial support from several government and academic initiatives, including funds ARQ001SOL-173-2022, PLEC2021-007903 and VEBPI, in addition to the Spanish Ministry of Science, Innovation and Universities. The main specimen, identified by the code MGB-512 and measuring around 50 centimeters, remains one of the centerpieces of the Barcelona Museum of Natural Sciences, proving that ancient collections still hold valuable secrets for modern science when analyzed with new technologies.
