During the Eocene (55 to 34 million years ago), Western Europe and East Asia formed two separate landmasses with very different mammalian faunas: European forests were home to endemic fauna such as the Paleotheran perissodactyls (an extinct group distantly related to modern mammals). modern horses, but more like our tapirs), adapted primates, choeropotamuses, and anaplothers (remotely related to modern pigs and cows), while Asia was inhabited by more cosmopolitans, including families of mammals found today on these two continents.
This dualism broke down 34 million years ago, at the very beginning of the Oligocene, a period of global climate change during which we move from the hot Earth called the “Greenhouse” to the Earth called the “Ice House” that we know today. This episode of climate change is caused by the first Antarctic glaciation, which follows a long period of falling CO2 atmospheric. Global cooling, which is estimated at around 5°C and is associated with a sharp drop in sea levels, is causing shocks to ecosystems and land connections between continents.
Then most of the endemic European mammals died out along with the appearance in Western Europe of a large number of taxa from Asia. This major renewal of the Western European fauna was named in 1909 by the Basel palaeontologist G. G. Stelin “Grande Coupure” – a term that is still widely used even outside the French-speaking world. This sudden arrival of Asian mammals at the beginning of the Oligocene is an important event in the history of the fauna of the Old World. However, fossils found in the Balkans indicate the presence of Asian mammals in southern Europe long before the Great Separation, suggesting an earlier colonization.
Our discovery of new fossils in Central Anatolia and reassessment of old fossils available in the Balkans, some of which date back to the XIXand show that for most of the Eocene, the region corresponding to the present-day Balkans and Anatolia was endowed with a terrestrial fauna that was homogeneous but distinct from that of Europe and East Asia.
This unique exotic fauna included marsupials of South American origin, embryopods (large herbivorous mammals resembling hippopotamuses) that previously lived on the African continent, primates that probably sailed on rafts over plant remains, and primitive ungulates close to those known only in the Paleocene (66– 56 million years ago). ). On the other hand, this endemic fauna is devoid of rodents, carnivores, equids or artiodactyls, which were numerous and diverse mammals in the Eocene of Eurasia. Much of our fieldwork in recent years has focused on documenting this fauna.
All this information allows us to outline the history of the third Eurasian continent, wedged between Europe, Africa and Asia and called “Balkanatolia”. Isolated from continental Eurasia in the early and middle Eocene, it then formed a low-relief continental mass, oscillating between an island continent and an archipelago depending on sea level, where endemic and archaic mammals flourished. This endemic fauna has a history that is still unknown: the continent of Balkanatolia is believed to have formed very early, possibly as early as the Upper Cretaceous (-70 million years ago), but this history has not yet been written. Balkanatolia can be compared to the current Indo-Australian archipelago, whose fauna differs significantly from mainland Asia, despite the short straits that separate them (this division follows the famous Wallace line, dedicated to its discoverer, naturalist Alfred Russel Wallace). This analogy applies at the geological level as well, since the Indo-Australian archipelago consists of several continental blocks characterized by specific ecosystems and separated by narrow and deep ocean basins.
A new place rich in fossils
Our discovery in Turkey of a new fossil-bearing site (Büyükteflek) dated 38-35 million years ago containing mammals of distinctly Asian origin, the oldest known to date in Anatolia, sheds light on the history of the Balkanatolian continent. These are fragments of the jaws of animals similar to large rhinoceroses, brontotheres, which became extinct at the end of the Eocene.
The remains of a small, slender gyracodont rhinoceros of Asian origin have also been discovered. The arrival of Asian taxa in Balkanatolia between 40 and 35 million years ago marks both the end of the endemism of the Balkanatolian faunas and the preliminary stage of the Great Cut. We believe that the arrival of Asian mammals in Balkanatolia was due to geographic changes that occurred in eastern Anatolia and the Caucasus during the Middle/Upper Eocene, certainly related to the closure of the Neotethys Ocean and uplift of the region after the collision. with the Asian continental margin.
These geographic shifts paved the way for the mammals that colonized Europe 34 million years ago, passing through Balkanatolia. Therefore, we believe that Balkanatolia played the role of a gateway between Asia and Europe during the settlement of mammals. The arrival of invasive Asian fauna and climate change associated with the Antarctic glaciation hastened the decline of endemic Balkan and later European fauna.
The original version of this article was published on The Conversation, a non-profit news site dedicated to exchanging ideas between academic experts and the general public.
Grégoire METAIS does not operate, advise, hold shares in, or receive funds from any organization that may benefit from this article, and does not claim affiliation other than its own research organization.