The Cretaceous Terrestrial Revolution (abbreviated KTR) describes the intense diversification of angiosperms, insects, reptiles, birds, and mammals during the Middle to Late Cretaceous (125-80 mya).Before Lloyd et al.'s 2008 paper described the KTR, it had been widely accepted in paleontology that new families of dinosaurs evolved during the Mid to Late Cretaceous, including the euhadrosaurs, neoceratopsians, ankylosaurids, pachycephalosaurs, carcharodontosaurines, troodontids, dromaeosaurs, and ornithomimosaurs. However, the authors of the paper have suggested that the apparent "new diversification" of dinosaurs during this time is due to sampling biases in the fossil record, and better preserved fossils in Cretaceous age sediments than in earlier Triassic or Jurassic sediments.
A comprehensive molecular study of evolution of mammals at the taxonomic level of family also showed important diversification during the KTR. Similarly, bee pollinator diversification strongly correlates with angiosperm flower appearance and specialization during the same era. For nearly the entirety of Earth's history, including most of the Phanerozoic eon, marine species diversity exceeded terrestrial species diversity, a pattern which was reversed during the Middle Cretaceous as a result of the KTR in what has been termed a biological "great divergence", named after the historical Great Divergence.
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