Short report on the 6th Palaeontological expedition of the National Museum of Natural History — BAS to the Upper Cretaceous vertebrate locality in the vicinity of the town of Tran

The 6th Palaeontological expedition to the fossil site with dinosaur and other vertebrate fauna of Late Cretaceous age near the town of Tran took place between 2nd and 11th August, 2023. The team was led by Assoc. Prof. Latinka Hristova from the National Museum of Natural History — BAS (NMNHS), and included palaeontologists from the museum, as well as scientists from the Sofia University and the Geological Institute at the Bulgarian Academy of Sciences.

The palaeontologists of the NMNHS describe the expedition as yet another successful season of field work.

Among the most intriguing fossil finds this year are several bones of large reptiles, including two vertebrae; half a dozen crocodylomorph teeth; possibly the first dinosaur tooth found at the fossil site so far; as well as some microvertebrate (i.e. vertebrate animals less than 1 kg in weight) bone fragments, probably belonging to amphibians. As was the case in previous years, most numerous were the fossils of fragmentary turtle shells. To the surprise of palaeontologists, most of the newly collected fossil material originates from rock beds which yielded only few fossils during previous expeditions. The last few days of field work were difficult for the team because of the unstable weather and occasional continuous rains. However, these difficulties did not prevent them from discovering many fossils.

During the last six years of field work near Tran, the palaeontologists have discovered the bone remains of at least two different kinds of non-avian dinosaurs, as well as the first fossils of Late Cretaceous pterosaurs, crocodylomorphs (teeth), pleurodiran turtles (mostly shells), and amphibians (long bone fragments) in Bulgaria. The dozens of collected fossils significantly expand the knowledge of the terrestrial and freshwater fauna which existed in the region some 83 million years ago. There are few terrestrial vertebrate fossil localities from this time known in Europe, and the Tran locality can compare to some of the richest of them. The data on the evolution of the European vertebrate faunas from 90 to 80 million years ago is still limited, which makes the contributions of our palaeontologists of high scientific value.

Everything that has been learnt since 2017, when the fossil locality was discovered, is helping scientists to reveal what kinds of animals lived in the region during the Late Cretaceous Epoch, when the Bulgarian lands were part of a vast tropical island archipelago, which covered most of the territory of modern day Europe. The study of the fossil material promises to answer questions about what the life was on these island and how dispersal and migration of different animal groups occurred — whether some animals migrated from Asia or Africa and dispersed across the archipelago, or if some endemic European taxa populated the islands through ‘island-hopping’ and then embarked on a journey to more distant landmasses.

For a third consecutive year undergraduate students in specialty Geology of the Sofia University joined the palaeontological team in search of dinosaurs. Some of them are already taking their first steps in the field of professional palaeontology by studying fossil material, which pertains to bony fishes and invertebrates and was collected at the fossil site with their participation.

After the mandatory preparatory work of the fossils of dinosaurs and other contemporary animals in the palaeontology laboratory at the NMNHS, which work includes removing of rock matrix and cleaning of the fossils, as well as assigning them unique inventory numbers, the scientists will reveal the results of their work before the wide palaeontological community in several scientific publications.

The palaeontological expedition ‘Tran 2023’ was financially supported by the Bulgarian National Science Fund (BNSF, Ministry of Education and Science, Bulgaria) for project ‘From dinosaurs to the earliest human ancestors: Fundamental studies of significant moments in the history of the fauna and the Human origins’ (Grant No. KP-06-N44/16).

You can learn more details about the work of the NMNHS’s palaeontologists in Tran this year, if you listen to the interview of Elisaveta Beleganska with Assoc. Prof. Latinka Hristova (in Bulgarian).

Interview with Assoc. Prof. Latinka Hristova and Vladimir Nikolov, both from NMNHS, and Assist. Prof. Docho Dochev from Sofia University by David Karaivanov from BulgariaONAir.