Fossils from the region provide insight into the evolutionary history of contemporary plants and animals. Four-hundred million years ago, when Hesse was still a great sea, it was populated by sponges, coral, sea lilies, mussles, snails and squid. Specimens of now extinct trilobites and armored fish bear witness to life in the Paleozoic era. By the Tertiary period, the world looked entirely different: basking sharks hunted manatee in shallow seas, and swamplands provided habitats for crocodiles, turtles, fish and frogs. The fossil remains of this plant and animal world stem from the Mainz Basin, a marine basin that covered, 38 to 12 million years ago, the present-day Rhenish Hesse region. Mammoths, forest elephants, hippopotamus, hyenas, deer and bears were found in younger sedimentation from the ancient Main river and the Lahn Hallow. The oldest of these fossils are some 890,000 years old, the youngest 20,000. In this period, symbiotic communities were shaped by a number of drastic changes in climate. Thermophilic species like the forest elephant were not contemporaries of the Tundra mammoth. Early humans of the Ice Age recorded images of their impressions of the world with great artistic skill in cave paintings.