Cat gap

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Gap in the fossil record

title: "Cat gap" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["extinction-events", "felids", "cats", "gaps-in-the-fossil-record"] description: "Gap in the fossil record" topic_path: "general/extinction-events" source: "https://en.wikipedia.org/wiki/Cat_gap" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Gap in the fossil record ::

The cat gap is a period in the fossil record of approximately 25 million 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 it 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

Main article: Felidae#Evolutionary history

::figure[src="https://upload.wikimedia.org/wikipedia/commons/3/36/Feliform_Timeline.svg" caption="Feliform evolutionary timeline"] ::

All modern carnivorans, including felids, evolved from miacoids, which existed from approximately 66 to 33 million years ago. There were other earlier cat-like species but Proailurus (meaning "before the cat"; also called "Leman's Dawn Cat"), which appeared about 30 million years ago, is generally considered the first "true cat".

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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 felids are descended from Pseudaelurus.

Nimravids, also known as false-sabertoothed cats, were a group of saber-toothed predators. Despite their cat-like appearance, they aren’t actually true cats, but instead a distinct family. Physically, some nimravids resembled the saber-toothed cat Smilodon, which would not appear until many millions of years later. Nimravids first appeared in North America around 40 Ma, with the appearance of Pangurban. The extinction of nimravids in North America marked the beginning of the "cat gap".

Possible causes

Hypercarnivorous tendency

The history of carnivorous mammals is characterized by a series of rise-and-fall patterns of diversification, in which declining clades are replaced by phylogenetically distinct but functionally similar clades. Over the past 50 million years, successive clades of small and large carnivorous mammals diversified and then declined to extinction. In most instances, the cause of the decline was energetic constraints and pervasive selection for larger size (Cope's rule) that lead to hypercarnivory dietary specialization. Hypercarnivory leads to increased vulnerability to extinction.

The nimravids were large cat-like animals that occupied this ecomorphic niche in the ecosystem until 26 Mya. It is highly likely that their hypercarnivory led to their extinction in North America. After the extinction of the nimravids, no other feliform or cat-like species were present in North America. This gap ended when felids arrived from Eurasia after crossing the Bering land bridge 18.5 million years ago. During this time there was great diversity among the other carnivorous mammals in North America – both hypocarnivorous and hypercarnivorous species – and other hypercarnivorous species existed before, during, and after the cat gap.

Changes in climate and habitat

::figure[src="https://upload.wikimedia.org/wikipedia/commons/2/2f/Leopard_on_the_tree.jpg" caption="Many cats tend to be [[arboreal]] hunters. The disappearance of forests in North America may have caused the mass extinction."] ::

Another possible explanation for the extinction of feliforms in North America is changes in the ecology of the continent. Evidence from the geologic temperature record shows that the earth was experiencing a period of global cooling, causing forests to give way to savannas. Nimravids, the cat-like predators present in North America at the time, favored forested environments, with a few exceptions such as Eusmilus, which showed more adaptations for open environments.

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", as well as the "entelodont gap". Faunal overturn at 25.8 Ma is the basis for division of the Arikareean time period (30.5–19 Ma), and the Arikareen NALMA (North American Land-Mammal Ages), into the Monroecreekian period (29.5–25.8 Ma), and then the Harrisonian period (25.8–23.5 Ma).

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Other

Volcanic activity has also been promoted as a possible cause of the cat gap as well as other extinctions during this time period. The La Garita Caldera is a large volcanic caldera located in the San Juan Mountains in southwestern Colorado, United States, and is one of a number of calderas that formed during a massive ignimbrite flare-up in Colorado, Utah, and Nevada during the Oligocene Epoch. The La Garita Caldera was the site of the Fish Canyon eruption, an enormous eruption about 27 million years ago. The scale of the Fish Canyon eruption was far beyond anything known in human history (erupting more than 10000 km3 for a VEI 8+ magnitude), and was possibly the most energetic event on Earth since the Chicxulub impact, which is thought by many paleontologists to have caused the extinction of the dinosaurs in the Cretaceous–Paleogene extinction event. The resulting explosive volcanism probably ejected large amounts of dust and debris into the stratosphere causing major cooling (see volcanic winter). Climatic effects could also have been caused by sulphur ejected into the stratosphere, which rapidly converts to sulphuric acid, an aerosol which cools the troposphere by blocking incoming solar radiation.

Another possible cause of the cat gap could have been the Late Cenozoic Ice Age that began 33.9 million years ago. This ice age caused glaciation in Antarctica that eventually spread to Arctic regions of southern Alaska, Greenland, and Iceland. Glaciers on the North American continent, as well as the cooling trend, could have made the ecosystem uninhabitable for feliformia cat-like species, although habitable for cold-weather caniformia species such as canids (dog-like species), mustelids (weasel-like species), and ursids (bear-like species).

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Evolution of caniforms during the gap

::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e6/Ysengrinia.jpg" caption="Some paleontologists argue that caniforms like [[Amphicyonidae]] – "bear dogs" - responded to the cat gap by evolving to become more cat-like, to fill the [[hypercarnivore]] [[ecological niche]]"] ::

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. This conclusion, however, is disputed.

::quote[attribution="molar]]s. In North America the first caniform group of moderate body size to move in the direction of hypercarnivory were the [[endemic]] [[Hesperocyoninae"] During or just prior to this "cat gap", numerous caniform species evolve catlike features indicative of hypercarnivory, such as reduced snouts, somewhat enlarged canines, and fairly extreme reduction of their crushing [[Molar (tooth) ::

However, other paleontologists take issue with this conclusion:

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References

References

  1. (2003). "Extinction and re-evolution of similar adaptive types (ecomorphs) in Cenozoic North American ungulates and carnivores reflect van der Hammens cycles". Naturwissenschaften.
  2. (2006). "Cats of Africa: Behavior, Ecology, and Conservation". Johns Hopkins University Press.
  3. (2022). "An early nimravid from California and the rise of hypercarnivorous mammals after the middle Eocene climatic optimum". Biology Letters.
  4. (2002). "The Auditory Region and Nasal Cavity of Oligocene Nimravidae". Journal of Vertebrate Paleontology.
  5. Antón, Mauricio. (2013). "Sabertooth". University of Indiana Press.
  6. (2016). "First nimravid skull from Asia". Scientific Reports.
  7. Antón, Mauricio. (2013). "Sabertooth". University of Indiana Press.
  8. Castellanos, Miguel (2024). [https://huskiecommons.lib.niu.edu/cgi/viewcontent.cgi?article=8874&context=allgraduate-thesesdissertations ''Hunting Types in North American Eocene and Oligocene Carnivores and Implications for Nimravid Extinction''] (Graduate Research Thesis & Disserations)
  9. Retallack, Gregory J.. (2004). "Late Oligocene bunch grassland and early Miocene sod grassland paleosols from central Oregon, USA". Palaeogeography, Palaeoclimatology, Palaeoecology.
  10. Flannery, Tim. (2002). "The Eternal Frontier: An Ecological History of North America and Its Peoples". Grove Press.
  11. Haggart, B. A.. (2000). "The Oxford Companion to the Earth". Oxford University Press.
  12. Wesley-Hunt, Gina D.. (2005). "The morphological diversification of carnivores in North America". Paleobiology.
  13. Van Valkenburgh, Blaire. (1999). "Major Patterns in the History of Carnivorous Mammals". Annual Review of Earth and Planetary Sciences.

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