Hungarian researchers have discovered an exceptionally rich dinosaur site in Transylvania

The Hațeg Basin in Transylvania is world-famous for its dinosaur remains, which have been unearthed from dozens of sites over the past century. Despite the high number of fossil localities, dinosaur finds are generally considered rare in the area. An exception is the newly discovered site, where researchers found more than a hundred vertebrate fossils per square meter — with the large dinosaur bones lying almost on top of each other.

The Valiora Dinosaur Research Group, consisting of Hungarian and Romanian paleontologists, has been conducting research for more than five years in the western part of the Hațeg Basin, an area famous for its dinosaur fossils. The Upper Cretaceous continental deposits studied here provide a glimpse into the final few million years before the extinction of the dinosaurs. During the excavations, the team collected assemblages containing thousands of vertebrate remains, including fossils of amphibians, turtles, crocodiles, dinosaurs, pterosaurs, and mammals. Among these, the K2 site stands out as the richest locality, yielding more than 800 vertebrate fossils from an area of less than five square meters. The detailed paleontological results of the site have recently been published in the scientific journal PLOS ONE.

“In 2019, during our first field survey in the Hațeg Basin, we almost immediately came across the K2 site. It was a defining moment for us — we instantly noticed dozens of large, exceptionally well-preserved black dinosaur bones gleaming in the grey clay layers exposed in the streambed. We immediately began our work, and through several years of excavation we collected an extraordinarily rich vertebrate assemblage from the site,” explained Gábor Botfalvai, assistant professor at the Department of Paleontology, Eötvös Loránd University, and leader of the research group.

Around 72 million years ago, the area now known as the Hațeg Basin was dominated by ephemeral rivers formed in a subtropical climate. These rivers flowed from elevated regions toward the basin, and during heavy rainfall, they frequently flooded, overflowing their banks. As they moved toward lower-lying areas, they picked up carcasses lying on the surface, as well as living animals or their remains that happened to be in their path.

“Detailed study of the rocks at the K2 site indicates that a small lake once existed here, which was periodically fed by flash floods carrying animal carcasses. As the flow of the rivers slowed rapidly upon entering the lake, the transported bodies accumulated in the deltaic environment along the shore, producing this exceptionally high bone concentration,” said Soma Budai, researcher at the University of Pavia and co-author of the publication.

The site yielded not only isolated bones but also several partial, associated dinosaur skeletons. These represent the remains of two different herbivorous dinosaur species. Some of the skeletons belong to a roughly two-meter-long, predominantly bipedal herbivore of the Rhabdodontidae family — one of the most common dinosaurs in the Hațeg Basin. The other type of skeleton, however, represents a major discovery: they belong to a titanosaurian sauropod dinosaur, of which no such well-preserved skeletons had previously been found in Transylvania. The study of these new fossils will provide valuable insights into the taxonomy of this long-necked dinosaur.

“Besides the remarkably high bone concentration, another key significance of this newly described site is that it represents the oldest known vertebrate accumulation in the Hațeg Basin. Studying this fossil assemblage allows us to look into the earliest composition of the Hațeg dinosaur fauna and trace the evolutionary directions and processes leading toward the dinosaurs known from younger Transylvanian sites — revealing how these Late Cretaceous ecosystems were similar or different from one another,” added Zoltán Csiki-Sava, associate professor at the University of Bucharest and Romanian leader of the research team.

The fossil assemblage described in this publication, along with other finds from ongoing excavations in the Hațeg Basin, will help scientists gain a more precise understanding of the evolutionary and ecological processes that shaped the composition of (Eastern) European dinosaur faunas during the Late Cretaceous.

The research was supported by the National Research, Development and Innovation Office of Hungary (NKFIH), the Supervisory Authority for Regulatory Affairs of Hungary, the Romanian Ministry of Research, Innovation and Digitalization, and the University of Bucharest.