Canidae
Proailurus
cat".[2
Pseudaelurus.
Felidae
Arikareean
Parenhydrocyon
the Old World
Temnocyon
Phoberocyon.[7]However
Ma
Nimravidae
Smilodon
Faunal
Chicxulub
Paleogene
Ridge
Mesocyon
Mammocyon
Megalictis
Canids
Nimravidae
Monroecreekian
Harrisonian
North American
North America
Miocene
the Middle Miocene
Bering
Asia
Cope
Eurasia
the San Juan Mountains
the Fish Canyon eruption
Earth
Antarctica
Arctic
the Arctic Ocean
the North Atlantic
The La Garita Caldera
Barbourofelidae
America
Colorado
United States
Utah
Nevada
Alaska
Greenland
Iceland
Scotland
Enhydrocyon
Daphoenodon
Cephalogale
North America."[8
the Oligocene Epoch
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.[1] The nimravids were large cat-like animals that occupied this ecomorphic niche in the ecosystem until 26 Ma. It is highly likely that their hypercarnivory led to their extinction in North America. Evidence from the geologic temperature record shows that the earth was experiencing a period of global cooling, causing forests to give way to savannas.[2] Climatic changes to arid conditions that muted variation at about 25.8 Ma coincides with the first appearance of hoglike creodonts and of pocket gophers, and this also is the beginning of the "cat gap" and the "entelodont gap", a period of some 7 million years when there were no nimravids, felids, or entelodonts in North America. As the salinity of the North Atlantic grew and as outflow of cold polar water increased, so the thermohaline circulation increased in vigour, providing the mild winter temperatures and large amounts of moisture to the North Atlantic, which are prerequisites to the build-up of the large continental ice caps on the adjacent cold continents.[6]It has been suggested by some that as a result of the cat gap caniforms (dog-like species including canids, bears, weasels, and other related taxa) evolved to fill more carnivorous and hypercarnivorous ecological niches that would otherwise have been filled by cats.[7] This conclusion, however, is disputed.[8]
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