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cat gap
The cat gap is a period in the fossil record of approximately 25 to 18.5 million years ago in which there are few fossils of cats or cat-like species found in North America. The cause of the "cat gap" is disputed, but may have been caused by changes in the climate (global cooling), changes in the habitat and environmental ecosystem, the increasingly hypercarnivorous trend of the cats (especially the nimravids), volcanic activity, evolutionary changes in dental morphology of the Canidae species present in North America, or a periodicity of extinctions called van der Hammen cycles)
==Cat evolution==
All modern carnivorans, including cats, evolved from miacoids, which existed from approximately 66 to 33 million years ago. Miacoid species gave rise to ''Proailurus'' (meaning "first cat"; also called "Leman's Dawn Cat"), which appeared about 30 million years ago, and is generally considered the first "true cat". There were other cat-like species before ''Proailurus'', but not within the family of the order Carnivora.
The increase in disparity through the early Miocene occurs during a time when few feliform fossils have been found in North America. The hypercarnivorous nimravid feliforms were extinct in North America after 26 Ma and felids did not arrive in North America until the Middle Miocene with the appearance of ''Pseudaelurus''. ''Pseudaelurus'' crossed over to North America by way of the Bering land bridge from surviving populations in Asia 18.5 million years ago. All modern-day cats are descended from ''Pseudaelurus''.
Nimravids were saber-toothed cat-like animals of the family Nimravidae. Although not "true cats" in the family Felidae, Nimravidae are considered to be a sister taxon to felids. They are basal feliforms, but their exact placement within Carnivora is still uncertain. Physically, Nimravidae resembled ''Smilodon'' (which would not evolve until many millions of years later). Nimravidae also became extinct in North America during the "cat gap."
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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