During the Mesozoic Era, a vast sea covered the territory in the Middle Volga Region. This area experienced both warm and cold currents, causing it to be the perfect breeding ground for new species of living beings. Among such vertebrate creatures were giant marine reptiles including plesiosaurs and pliosaurs, as well as crocodiles and turtles. These large creatures were also surrounded by hundreds of smaller species of mollusks. This wide variety of sea creatures served as a source of food for each other. Millions of years after their existence and demise, the remains and fossils of the creatures that lived during this period have been uncovered as a result of tectonic activity and the erosion of ancient rocks from the Jurassic and Carboniferous periods. Today, in the northern part of Ulyanovsk Oblast, near the village of Undory, paleontologists have found the rarest remains of ancient life on the planet, hidden in the layers of rock that make up the area’s coastal slopes.