Paleontologists have unearthed one of Europe's richest dinosaur fossil sites in Romania's Hațeg Basin, where bones accumulated in extraordinary density 72 million years ago. The discovery at the K2 site includes the first well-preserved titanosaur skeletons from the region, shedding light on Late Cretaceous ecosystems. This find highlights how ancient floods trapped thousands of remains in a prehistoric lake.
The Hațeg Basin in Transylvania has yielded dinosaur fossils for over a century, but complete specimens remain rare. That changed with the K2 site, identified by the Valiora Dinosaur Research Group—a team of Hungarian and Romanian paleontologists—during fieldwork spanning more than five years in the western basin. The site's rocks date to the Upper Cretaceous, capturing the era's final moments before the dinosaurs' extinction.
In 2019, the team spotted the site's potential during their initial survey. "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," said Gábor Botfalvai, assistant professor at Eötvös Loránd University and the group's leader. From an area under five square meters, they recovered over 800 vertebrate fossils, including amphibians, turtles, crocodiles, dinosaurs, pterosaurs, and mammals—exceeding 100 fossils per square meter.
Geological analysis points to a small lake fed by flash floods around 72 million years ago, in a warm subtropical climate. Rivers overflowed during heavy rains, sweeping in carcasses that piled up as waters slowed in the delta. "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... producing this exceptionally high bone concentration," explained Soma Budai, a co-author from the University of Pavia.
Among the haul are partial skeletons of two plant-eating dinosaurs: a two-meter-long rhabdodontid, common in the basin and likely bipedal, and a titanosaurian sauropod—marking the first such well-preserved find in Transylvania. This oldest vertebrate accumulation in the basin offers insights into evolving dinosaur faunas. "Studying this fossil assemblage allows us to look into the earliest composition of the Hațeg dinosaur fauna and trace the evolutionary directions... revealing how these Late Cretaceous ecosystems were similar or different," noted Zoltán Csiki-Sava, associate professor at the University of Bucharest and the Romanian team leader.
These fossils, detailed in a recent PLOS ONE publication, refine understandings of Eastern European dinosaur communities amid environmental shifts near the Cretaceous' end. Ongoing excavations promise further revelations about these ancient ecosystems.