Ultraviolet imaging of a 125-million-year-old crocodylomorph fossil has revealed unexpectedly detailed traces of skin, sensory structures, and chest cartilage.
More than a century after a tiny Early Cretaceous crocodylomorph was unearthed in northeastern Spain, its fossil is revealing details that were hiding in plain sight. Under ultraviolet light, researchers have now detected exceptionally preserved traces of skin, possible color patterning, and chest cartilage in Montsecosuchus depereti – features that offer a rare glimpse of how this 125-million-year-old animal looked and functioned in life.
The new study, published in the Zoological Journal of the Linnean Society, provides the first detailed description of the fossil’s soft tissues. Discovered at the Pedrera de Meià site in Catalonia, the specimen is shedding new light on both the appearance of early crocodylomorphs and the evolution of anatomical features that would later characterize modern crocodilians.
Around 125 million years ago, a small crocodile died in a karst lake near the coast of what is now the Catalan Pre-Pyrenees. Its remains settled into fine lake sediments that later formed the lithographic limestone deposits of Pedrera de Meià, located within the UNESCO Orígens Global Geopark. These exceptional conditions allowed the fossil to preserve far more than just its bones.
The fossil, cataloged as MGB-512, measures about 50 centimeters (20 inches) long and is housed at the Museum of Natural Sciences of Barcelona. Although it was discovered more than 100 years ago and received limited study during the 1990s, researchers have now uncovered remarkable new details about the shape and distribution of its preserved soft tissues.
UV Light Uncovers Hidden Crocodile Anatomy
While building a database of fossils from the Montsec lithographic limestones held in museums across Catalonia and Europe, paleontologists Oscar Castillo and Jesús Serrano noticed unusual structures on the Montsecosuchus depereti holotype under ultraviolet light. The technique causes fossilized soft tissues to fluoresce differently than the surrounding rock, exposing features that remain invisible under ordinary lighting.
“UV light allows us to see details that would otherwise remain completely hidden in the rock,” explains Oscar Castillo-Visa, first author of the work.
Using this approach, the team identified several types of soft tissue, including preserved epidermal scales. Although the species has been known since the early 20th century, this is the first detailed description of its skin. The findings reveal wide variation in the size and shape of scales across the body and show that the animal lacked the tall tail fin seen in modern crocodiles.
Researchers also found evidence suggesting the presence of sensory organs within some scales, particularly around the neck, limbs, and the sides of the body and tail. In living crocodiles, these organs detect touch, changes in water pressure, temperature, and chemical signals. Their restricted distribution in Montsecosuchus suggests these sensory structures may have first evolved in localized regions before spreading across the entire body in later crocodilian ancestors.
Ancient Crocodile Skin and Respiratory Evolution
Ultraviolet imaging also exposed cartilage within the chest, indicating that Montsecosuchus had a well-developed respiratory system with similarities to modern crocodiles. The discovery suggests that some early crocodylomorphs had already evolved complex chest anatomy early in their evolutionary history.
“These traits indicate that, despite being a primitive animal, it was already very well adapted to a semi-aquatic lifestyle,” concludes Castillo-Visa.
One of the study’s most striking discoveries is evidence of preserved tail coloration. Ultraviolet light revealed alternating light and dark bands across scales on the tail, which researchers believe represent the animal’s original color pattern. These markings may have provided disruptive camouflage by breaking up the animal’s outline. If confirmed, Montsecosuchus would be the oldest known crocodylomorph with preserved coloration.
“At the moment we cannot say for sure what color the crocodile’s tail was, but it would be expected that it was not so different from current species, which also show different coloration patterns,” explains Albert G. Sellés, co-author of the article.
Oldest Preserved Crocodylomorph Coloration
The findings offer new insight into the early evolution of crocodylomorph skin, respiration, and external anatomy. They also highlight the scientific importance of the Catalan fossil record for understanding vertebrate evolution.
Pedrera de Meià is classified as a Konservat-Lagerstätte, a rare type of fossil site where soft tissues, as well as bones, are exceptionally preserved. Because of its remarkable fossils, the site has become an important resource for studying Early Cretaceous fish, amphibians, reptiles, and plants. More than 8,000 fossil specimens have been recovered so far.
Visitors can see many of these fossils at the Montsec de Meià Interpretation Center in Vilanova de Meià, where more than 100 exceptionally preserved specimens are on display. The Orígens Geopark also offers a website featuring many of the site’s most significant fossils.
Among the fossils are spiders, flies, wasps, beetles, insect larvae, crustaceans, fish, amphibians, and an exceptional collection of plants, including Montsechia, recognized as the world’s earliest known flowering plant. The interpretation center is part of the “Dinosaurs of the Pyrenees” project, a network of museums and visitor centers dedicated to showcasing the rich paleontological heritage of the Catalan Pyrenees.
Reference: “Soft tissue preservation in the Barremian Montsecosuchus depereti (Neosuchia: Atoposauridae)” by Oscar Castillo-Visa, Phil R Bell, Àngel Galobart and Albert Sellés, 13 June 2026, Zoological Journal of the Linnean Society.
DOI: 10.1093/zoolinnean/zlag076
The research has been mainly funded by the VEBPI, PLEC2021-007903, and ARQ001SOL-173-2022 projects, with support from the Ministry of Science, Innovation and Universities, the NextGenerationEU/PRTR program, the Department of Culture of the Generalitat de Catalunya, and the CERCA program.
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