Related by context. Frequent words. (Click for all words.) 63 mass extinction 60 mass extinctions 58 megafauna 55 Cretaceous Period 54 extinctions 54 vertebrate species 53 multicellular 52 supernova explosion 51 amphibian species 51 plesiosaur 50 mammals 50 hominid 50 Homo habilis 50 tyrannosaur 50 single celled organisms 50 glaciation 50 Ardipithecus 49 dinosaurs roamed 49 dinosaurs 49 overhunting 49 fossilized remains 49 Late Cretaceous 49 Homo sapiens 49 mammoths 49 Oetzi 49 Australopithecus afarensis 49 species extinctions 48 Eta Carinae 48 volcanism 48 volcanic eruptions 48 interglacial 48 tetrapods 48 carnivorous dinosaurs 48 terrestrial ecosystems 48 trilobites 47 Homo erectus 47 Tunguska 47 mammal species 47 Archaeopteryx 47 fossils 47 Tasmanian tiger 46 hominids 46 anatomically modern 46 woolly mammoth 46 mammal 46 asteroid 46 Australopithecus 46 prehistoric creatures 46 pygmy elephants 46 volcanic eruption 46 single celled 46 vertebrate 46 woolly mammoths 45 Homo floresiensis 45 hominins 45 gigatonnes 45 vertebrates 45 Mesozoic 45 Ice Age 45 cataclysmic 45 supernova explosions 45 Denisovans 45 gamma ray burst 45 dwarf galaxy 45 thylacine 45 coelacanth 45 comet 44 Cretaceous 44 journal Geology 44 Little Ice Age 44 multicellular organisms 44 extinct species 44 Komodo dragons 44 hominin 44 Pleistocene 44 fossil 44 PETM 44 Precambrian 44 baiji 44 species 44 Tyrannosaurus rex 44 Ocean acidification 44 western lowland gorillas 44 ocean acidity 44 atmospheric carbon dioxide 44 permafrost 43 plate tectonics 43 humans 43 T. rex 43 Carboniferous 43 protective ozone layer 43 arthropod 43 theropods 43 sauropod 43 volcanic activity 43 greenhouse warming 43 geologic 43 magnetar 43 supermoon 43 comet nucleus 43 chytrid fungus