A 240-Million-Year-Old Fossil Disappeared for 20 Years — Its Rediscovery Revealed a New Reptile Related to Dinosaurs and Crocodiles
A fossil discovered in southern Brazil has taken scientists on an unusual journey through time after part of the specimen disappeared for more than two decades. Its eventual rediscovery helped researchers identify a previously unknown reptile that lived around 240 million years ago, during the Middle Triassic Period.
The newly named species, Silescelida acristata, was found near Dona Francisca in Brazil’s Rio Grande do Sul state, within the geological region of the UNESCO-recognized Quarta Colônia Geopark. The animal lived relatively soon after the devastating Permian–Triassic mass extinction, when terrestrial ecosystems were undergoing major ecological changes.
Silescelida was not a dinosaur or a crocodile. Instead, it belonged to the broader archosauriform group, a lineage that includes evolutionary branches leading toward dinosaurs, birds, crocodiles and their extinct relatives. Its anatomy therefore provides a glimpse into an important period before those better-known groups became dominant.
The animal was relatively small and is described as a slender, four-legged predator roughly comparable in size to a small alligator. Researchers were particularly interested in its limb anatomy, including the structure of its thigh bone, which suggests a more semi-erect posture than that of many earlier reptiles.
That posture could have helped the reptile move more efficiently across the ground. Such changes in limb orientation are important because increasingly efficient terrestrial locomotion became one of the features associated with the evolutionary diversification of archosauriforms.
The fossil’s scientific importance became clear only after a missing portion was rediscovered. Part of the specimen had been accidentally lost for more than 20 years, but researchers located the missing material during a technical visit to the paleontological collection at the Pontifical Catholic University of Rio Grande do Sul in 2022.
Recovering the missing material allowed scientists to establish the specimen’s provenance and conduct the detailed anatomical and evolutionary analysis necessary to recognize it as a new species. The discovery demonstrates how even incomplete fossil material can become scientifically valuable when collections are carefully preserved and older specimens are reexamined.
The researchers also found that Silescelida may have affinities with the Euparkeriidae, a relatively poorly understood group of early archosauriforms. Fossils associated with this group have largely been known from Africa, Asia and Europe, making the Brazilian discovery significant for understanding their geographic distribution during the Triassic.
Its presence in South America suggests that these early relatives of dinosaurs and crocodiles may have been more widely distributed than the fossil record previously indicated. The finding adds another piece to the complicated evolutionary history of archosauriforms before dinosaurs emerged as major terrestrial animals.
The species name itself preserves the story of its unusual history. Silescelida combines references to “silence” and “leg,” reflecting both the long period during which part of the fossil was missing and the importance of the preserved limb bones. The species name acristata, meaning “without a crest,” refers to a distinctive absence on the femur that helps separate it from close relatives.
The discovery highlights an important lesson in paleontology: scientific breakthroughs do not always require a newly excavated fossil. Sometimes, a specimen already sitting in a museum collection can reveal something entirely new when it is rediscovered, examined with modern methods and placed into a better-understood evolutionary framework.
For researchers studying the origins of dinosaurs and crocodiles, Silescelida acristata provides another rare glimpse into the evolutionary experimentation taking place roughly 240 million years ago. Its story also shows why preserving and revisiting fossil collections can continue to reshape our understanding of Earth’s deep past.
