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The Cenozoic is Earth's current geological era, representing the last 66 million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configuration of continents. It is the latest of three geological eras since complex life evolved, preceded by the Mesozoic and Paleozoic. It started with the Cretaceous–Paleogene extinction event, when many species, including the non-avian dinosaurs, became extinct in an event attributed by most experts to the impact of a large asteroid or other celestial body, the Chicxulub impactor.
The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words μείων and καινός and means "less recent" because it has 18% fewer modern marine invertebrates than the Pliocene has. The Miocene is preceded by the Oligocene and is followed by the Pliocene.
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present. As with other older geologic periods, the rock beds that define the epoch are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The name Oligocene was coined in 1854 by the German paleontologist Heinrich Ernst Beyrich from his studies of marine beds in Belgium and Germany. The name comes from the Ancient Greek ὀλίγος and καινός, and refers to the sparsity of extant forms of molluscs. The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period.
The Pliocene is the epoch in the geologic time scale that extends from 5.333 million to 2.58 million years ago. It is the second and most recent epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian Stage, which lasted from 2.588 to 1.806 million years ago, and is now included in the Pleistocene.
Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene, spread to Europe by the late Eocene, and appear in Asia, and Africa by the early Miocene. They had largely disappeared worldwide by the late Miocene, with the latest recorded species at the end of the Miocene in Pakistan. They were among the first carnivorans to evolve large body size. Later in their history, they came into competition with hesperocyonine and borophagine canids. As dogs evolved similar body sizes and cranial and dental adaptations, the rise of these groups may have led to their extinction. Amphicyonids are often colloquially referred to as "bear-dogs".
Caniformia is a suborder within the order Carnivora consisting of "dog-like" carnivorans. They include dogs, bears, raccoons, and mustelids. The Pinnipedia are also assigned to this group. The center of diversification for the Caniformia is North America and northern Eurasia. Caniformia stands in contrast to the other suborder of Carnivora, the Feliformia, the center of diversification of which was in Africa and southern Asia.
Entelodontidae is a extinct family of pig-like artiodactyls which inhabited the Northern Hemisphere from the late Eocene to the Middle Miocene epochs, about 38-19 million years ago. Their large heads, low snouts, narrow gait, and proposed omnivorous diet inspires comparisons to suids and tayassuids (peccaries), and historically they have been considered closely related to these families purely on a morphological basis. However, studies which combine morphological and molecular (genetic) data on artiodactyls instead suggest that entelodonts are cetancodontamorphs, more closely related to hippos and cetaceans through their resemblance to Pakicetus, than to basal pigs like Kubanochoerus and other ungulates.
Peltephilus, the horned armadillo, is an extinct genus of dog-sized, armadillo xenarthran mammals which first inhabited Argentina during the Oligocene epoch, and became extinct in the Miocene epoch. Notably, the scutes on its head were so developed that they formed horns. Aside from the horned gophers of North America, it is the only known fossorial horned mammal.
Archaeotherium is an extinct genus of entelodont artiodactyl endemic to North America during the Eocene and Oligocene epochs (35—28 mya), existing for approximately 9.1 million years. Archaeotherium fossils are most common in the White River Formation of the Great Plains, but it has also been found in the John Day Basin of Oregon and the Trans-Pecos area of Texas.
Amphicyon is an extinct genus of large carnivorous bone-crushing mammals, popularly known as bear dogs, of the family Amphicyonidae, subfamily Amphicyoninae, from the Burdigalian Epoch until the late Pliocene. Members of this family received their vernacular name for possessing bear-like and dog-like features. They ranged over North America, Europe, Asia, and Africa from 16.9 to 2.6 Ma ago, existing for approximately 14.3 million years.
Hemicyon, also known as the "dog-bear", is an extinct genus of hemicyonine bear, which probably originated in Eurasia but was found in Europe, Asia and North America during the Miocene epoch, existing for approximately 16 to 13 mya. Hemicyon is the best-known genus in the Hemicyoninae, a subfamily intermediate between bears and their Caniform ancestors but most often classified as bears. Hemicyonid bears should not be confused with Amphicyonids (bear-dogs), which are their own separate family of carnivores.
Metamynodon is an extinct genus of amynodont rhino that lived in North America and Asia from the late Eocene until early Oligocene, although the questionable inclusion of M. mckinneyi could extend their range to the Middle Eocene. The various species were large, displaying a suit of semiaquatic adaptations similar to those of the modern hippopotamus despite their closer affinities with rhinoceroses.
Daeodon is an extinct genus of entelodont even-toed ungulates that inhabited North America about 23 to 20 million years ago during the latest Oligocene and earliest Miocene. The type species is Daeodon shoshonensis, described by a very questionable holotype by Cope. Some authors synonimize it with Dinohyus hollandi and several other species, but due to the lack of diagnostic material, this is questionable at best.
Daphoenus is an extinct genus of bear dogs. Daphoenus inhabited North America from the Middle Eocene to the Middle Miocene, 37.2—16.0 Mya, existing for approximately 21 million years.
Notohippidae is a paraphyletic extinct family of notoungulate mammals from South America. Notohippids are known from the Eocene and Oligocene epochs.
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, changes in the habitat and environmental ecosystem, the increasingly hypercarnivorous trend of the cats, 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.
Paraentelodon is an extinct entelodont from the Late Oligocene and Oligocene-Miocene boundary of Asia. The fossils of the type species P. intermedium were found in Georgia, Kazakhstan and China. An indeterminate species represents in Bugti Hills which is the late Oligocene of Pakistan.
Hyaenodonta is an extinct order of hypercarnivorous placental mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that arose during the early Paleocene in Europe and persisted well into the late Miocene.
Ankylorhiza is an extinct genus of toothed whale that lived in what is now the United States during the Oligocene epoch, between 29 and 23.5 million years ago. The type and only known species is A. tiedemani, though two fossil skeletons may represent an additional, second species within the genus. Ankylorhiza was about 4.8 meters (16 ft) long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.
Delotrochanter is an extinct genus of large-sized carnivoran mammals, belonging to the Amphicyonidae, that lived in the Great Plains of North America during the Oligocene to Early Miocene. This genus includes some of the largest and last surviving members of the subfamily Temnocyoninae. it furthermore possesses adaptions towards both bone-crushing and cursoriality.
References
- ↑ "ICS Timescale Chart". www.stratigraphy.org.
- ↑ Lucas, Spencer G.; Blodgett, Robert B.; Lichtig, Asher J.; Hunt, Adrian P. (2022-08-02). FOSSIL RECORD 8. New Mexico Museum of Natural History and Science. pp. 400–401.
- ↑ Raffery, John, ed. (2010-08-15). The Cenozoic Era: Age of Mammals. The Rosen Publishing Group, Inc. pp. 104–105. ISBN 978-1-61530-144-7.
