A group of Russian palaeontologists, including specialists from St Petersburg University, together with colleagues from Bonn University described two new species of primitive mammals that lived on Earth at the beginning of the Cretaceous period, about 120 million years ago.

These and many other findings at the Teete stream in the Suntarsky district of the Republic of Sakha enabled scientists to understand that during the age of dinosaurs the ecosystem of Yakutia was practically «preserved» and has not changed for 40 million years. The results of the research are published in the journal Plos One.

Both of the primitive animals resembled modern shrews, but they are not related as the ancient branch lived and died out in the Cretaceous period. Most likely, they were replaced by more developed placental mammals. The animals fed on insects and lived quite actively. Whether they lived on the ground, in the water or in the crown of trees is still difficult to say, because palaeontologists have not found whole skeletons, only several fragments of their jaws with teeth. The length of the largest find is about five millimetres.

«They are representatives of two groups of primitive mammals — eutriconodonts and docodonts. The first teeth looked like small tridents — three of their peaks stand in one line, which is a very primitive structure. But docodonts tried to complicate their teeth: they have more tubercles and have a chewing surface,» said Pavel Skuchas, a specialist in Mesozoic Vertebrates and Associate Professor of St Petersburg University.

Mammals have received unusual names: Khorotherium yakutensis and Sangarotherium aquilonium. The first name mentions Yakutia, as well as the village of Khoro whose residents, as the researchers note, have participated in excavations at the site of the dinosaurs of Teete for several years. The second animal was named in honour of the Sangar series — the geological layer in which the bones were found, and its specific name aquilonium is translated from Latin as «northern».

Pavel Skuchas notes that he and his colleagues from the Zoological Institute of the Russian Academy of Sciences, Kazan Federal University, Bonn University (Germany), the AA Borisiak Paleontological Institute of the Russian Academy of Sciences, and the Institute of Geology of Diamond and Noble Metals of the SB RAS found fragments of animal skeletons during last year’s expedition at the Teete location. It is located near the Yakut city of Suntar. Here, by the way, bones of dinosaurs have already been found, but the place is still considered insufficiently studied.

During the age of dinosaurs, these territories were located close to the north pole. So for researchers they open a whole window into the polar world of the Cretaceous period, about which little is known. Did the local fauna differ from the one that inhabited the southern regions? What was the climate here? How were the animals affected by the polar day and the polar night? Although palaeontologists are expected to answer all these questions in the future, the latest findings have already helped to learn about something new.

Source: Plos One Journal

«Primitive mammals, which we have found in the Cretaceous sediments, are actually the ‘living fossils’ of their time,» said Pavel Skuchas. «It is believed that between the Jurassic and Cretaceous periods a fairly serious extinction occurred, as a result of which many species died. Our findings, as well as recent research of our colleagues, suggest that there has been no global change of fauna and ecosystem rearrangement in Siberia. There have been no fatal events for some 40 million years — it’s a long time. For comparison: the first human beings appeared on Earth about 2.5 million years ago.»
The researcher also noted that the climate in the age of dinosaurs on the territory of modern Yakutia was, most likely, moderate and free of frost, but slightly cooler than in Western Siberia. This is evidenced by the fact that palaeontologists did not discover the bones of ancient crocodiles. Apparently, for them this weather was not the most comfortable. But there were lizards, amphibians, mammals, turtles, and a variety of dinosaurs. It is in the quest for them that the research team will go to the Teete creek for the second time: the expedition will start at the end of July.