Published in the Zoological Journal of the Linnean Society, the new research provides the first detailed description of preserved soft tissue in Monsecosuchus depereti, a small crocodile relative discovered at the Pedrera de Meià fossil site in Lleida, Catalonia. Using ultraviolet light, researchers identified new evidence of its skin, sensory structures, respiratory anatomy and possible color patterns. The study was led by the Miquel Crusafont Catalan Institute of Paleontology.

A Small Crocodile Preserved for 125 Million Years

About 125 million years ago, a small crocodile died in a karst lake near the coast of what is now Catalonia’s Pre-Pyrenees. Its body sank into fine lake sediment, where unusually favorable conditions preserved it in remarkable detail. Over time, those deposits became the limestone of Pedrera de Meià, now part of the Origens UNESCO Global Geopark.

Cataloged as MGB-512, the fossil is about 50 centimeters long and is housed at Barcelona’s Museum of Natural Sciences. Although it was discovered more than a century ago and received scientific attention in the 1990s, the latest analysis has revealed information hidden since its discovery, including the shape and distribution of preserved soft tissue.

The breakthrough came as paleontologists Oscar Castillo and Jesús Serrano were compiling a database of fossils from Montsec slate limestone held in museums across Catalonia and Europe. When they examined the Monsecosuchus depereti holotype under ultraviolet light, they noticed structures that appeared to be preserved soft-tissue remains.

Ultraviolet light changes how fossilized tissue and surrounding rock behave, highlighting structures that would otherwise remain invisible.

“Ultraviolet light allows us to see details that would otherwise be completely hidden in the rock,” explains Oscar Castillo-Visa, the study’s lead author.

Ultraviolet Light Reveals Ancient Crocodile Skin

Using ultraviolet imaging, the research team documented several types of soft tissue, including epidermal scales. Although Monsecosuchus depereti has been known to science since the early 20th century, this analysis provides the first detailed view of its skin.

The scales varied considerably in shape and size depending on their location on the body. Researchers also found that the animal lacked the tall caudal fins seen in modern crocodiles.

The fossil may preserve traces of sensory organs embedded in the skin. Possible structures appear inside some scales, particularly around the neck and limbs and along the sides of the body and tail.

In living crocodiles, similar sensory organs can detect touch and changes in water pressure, while also responding to temperature and chemical signals. In Monsecosuchus, these possible sensory structures appear only in small scales around the body’s edges. This distribution may indicate that such organs first evolved in localized areas before spreading more widely across the skin in later crocodilian lineages.

Clues to an Early, Efficient Respiratory System

Ultraviolet analysis also revealed cartilage structures in the thoracic region. These features indicate that Monsecosuchus already had an efficient respiratory system and shared certain anatomical similarities with modern crocodiles.

The discovery suggests that sophisticated thoracic anatomy evolved surprisingly early in crocodilian history.

“These characteristics indicate that, despite being a primitive animal, it was already very well adapted to a semi-aquatic lifestyle,” Castillo-Visa concludes.

Possible Color Patterns Preserved on the Tail

One of the most striking findings concerns the animal’s tail.

Under ultraviolet light, some tail scales displayed alternating light and dark bands. Researchers interpret these bands as possible evidence of the animal’s natural coloration.

The pattern may have provided disruptive camouflage, breaking up the crocodile’s outline and making it harder to distinguish from its surroundings. If confirmed, Monsecosuchus would be the oldest known crocodilian with preserved evidence of coloration.

Scientists have not yet determined the exact colors that produced the pattern.

“At this point, we can’t say exactly what color the crocodile’s tail was, but we expect it to be not that different from modern species, which also show different color patterns,” explains Albert G. Serres, a co-author of the study.

Why the Fossil Matters

The discovery provides new clues about the early evolution of crocodilian skin, respiration and external anatomy. It also highlights the scientific importance of Catalonia’s fossil record for reconstructing vertebrate evolution.

In addition to Oscar Castillo-Visa and Albert G. Serres, the study involved Ángel Gallobart of the University of New England, who is also director of the Miquel Crusafont Catalan Institute of Paleontology and the Conca Dellà Museum, as well as Phil Bell.

The research was primarily funded through the VEBPI, PLEC2021-007903 and ARQ001SOL-173-2022 projects. Additional support came from the Ministry of Science, Innovation and Universities, the NextGenerationEU/PRTR program, the Catalan Cultural Agency and the CERCA program.

Pedrera de Meià: An Exceptional Fossil Site

Pedrera de Meià is a Conservato Lagerstätte, a term used to describe fossil deposits with exceptional preservation. At these sites, fossils may retain not only bones and other hard tissues but also delicate soft structures that are usually lost during fossilization.

This extraordinary preservation makes Pedrera de Meià an important location for studying Early Cretaceous fish, amphibians, reptiles and plants. More than 8,000 fossil specimens have been discovered there.

Fossils from the site can be viewed at the Meià Basin Interpretive Center in Vilanova de Meià. More than 100 highly preserved specimens are displayed there. The Origens Geopark also provides information on its website, where many representative fossils from the site are featured.

The fossil record includes spiders, flies, wasps and beetles, insect larvae, crustaceans, fish, amphibians and a remarkable diversity of plants. Among them is Montsechia, considered the world’s first known angiosperm. The center is also part of the “Dinosaurs of the Pyrenees” project, a network of museums and interpretive centers that showcase the rich paleontological record of the Catalan Pyrenees.