In a tabloid, a headline like “Crocodile in a Mine” might at first glance sound like a silly summer story. However, we have an important scientific report. What is it about? Researchers at the University of Warsaw are seeking, among other things, an answer to the question: what do the alligator remains found in the Bełchatów Lignite Mine tell us about the climatic and geological history of our planet and its fauna?
Mysteries: The Earth’s past and future
The find itself is unassuming – measuring 29 by 32 mm. Both the front portion of the bone and the fragment located to the right of the central keel (a sharply pointed bony ridge) are missing, and the tip of the keel is also damaged. The outer surface is covered with circular pits and holes. Some of them are connected. On the other, inner side, we see a smooth surface with small holes. On the left, near the edge, there is a distinctive indentation, a trace of damage. Its origin cannot be determined today. This is hardly surprising – the described remains are approximately 17 million years old.
This is a fragment of a dorsal osteoderm, a bony structure found in the skin of certain reptiles, among others. This particular reptile was a crocodile. The remains were found in the lake sediments of the “Szczerców” Field in the Bełchatów Lignite Mine. It was quickly determined that they most likely belonged to a Diplocynodon. This is a crocodile from the alligator family, reaching a length of 1 to 3 meters. In addition to the osteoderm, the research team also described fragments of crocodile teeth from other sites.
Returning to the osteoderm – this is a valuable discovery, and it’s not just the age that makes it significant. We’re talking about the northernmost crocodile fossil among those dating back as far as 23 million years. And yet, the presence of these animals is typical of subtropical and tropical regions…
From bones to Earth’s history
Scientists from the Faculty of Geology and the Faculty of Biology at the University of Warsaw, working in National Science Centre (NCN) grant project* made this groundbreaking discovery with the participation of researchers from the Polish Academy of Science and the Moravian Museum. The goal of the project is to determine the role of the northern coast of the ancient Paratethys Sea in the exchange of fauna between Europe and Asia during the Miocene, an epoch spanning approximately 23 to 5.3 million years ago. At that time, the landscape underwent significant changes, including the uplift of new mountain ranges that affected climate and water circulation. In the Miocene, one branch of the Paratethys Sea extended into what is now southern Poland; its deposits contributed to the formation of the Carpathians, while others filled the Fore-Carpathian Basin north of the range.
[fotografia]
The question facing scientists is: did this region serve as a major intercontinental corridor facilitating the dispersal of terrestrial vertebrates? This question is accompanied by a second one: how did the cooling of the climate that occurred in the second half of the Miocene affect the composition of thermophilic vertebrate faunas north of the Paratethys Sea (i.e., the region of today’s Carpathians, the Fore-Carpathian Basin, and Central Poland)?
What does this mean – what lies ahead?
Diplocynodon, as has been claimed so far, primarily inhabited freshwater environments. Meanwhile, some of the described finds (teeth) are closely associated with Paratethys marine sediments, which suggests the possibility that these reptiles were tolerant of seawater. In that case, the migration route enabling the spread of crocodiles northward would have included not only the freshwater basins of central Poland but also the marine Paratethys basin.
Following the cooling of the climate that began in the Middle Miocene, the diversity and distribution of crocodilians in the Northern Hemisphere began to decline gradually. These reptiles never again exceeded their previous latitudinal limits, which are most likely marked by the recently discovered alligator remains. The Miocene was the last such warm and humid epoch in Earth’s history. It is therefore hard not to ask whether the current climate warming might mean that our freshwater and saltwater environments will once again be inhabited by reptiles similar to Diplocynodon, for example?
“Earth’s history teaches us that even if certain phenomena are long-lasting, they do not last forever. This also applies to climatic phenomena. Sooner or later, the climate in Poland will change to become favorable for the presence of these giant reptiles. When exactly will this happen, and to what extent will human activity contribute to it (human activity that has also severely depleted the global crocodile population, bringing some species to the brink of extinction…)? Given the current state of knowledge, we can only speculate.” says Dr. Marcin Górka of the Faculty of Geology at the University of Warsaw.
*“New Miocene land vertebrates from the northwestern Paratethys shores and their implications for Eurasian faunal exchange”
** Link to the article: Crocodylian remains from the Miocene of the Fore-Carpathian Basin and its foreland – including the world’s northernmost Neogene crocodylian
The text was originally published in Polish on the Serwis Naukowy UW website on July 25, 2025. It was updated in June 2026.
