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The Cenozoic is also known as the Age of Mammals because the terrestrial animals that dominated both hemispheres were mammals – the eutherians in the Northern Hemisphere and the metatherians (marsupials, now mainly restricted to Australia and to some extent South America) in the Southern Hemisphere. The extinction of many groups allowed ...
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after creta, the Latin word for the white limestone known as chalk.
All major Late Cretaceous mammalian lineages, including monotremes (egg-laying mammals), multituberculates, metatherians (which includes modern marsupials), eutherians (which includes modern placentals), meridiolestidans, [148] and gondwanatheres [149] survived the K–Pg extinction event, although they suffered losses.
Mammals had first appeared in the Late Triassic, and remained small and nocturnal throughout the Mesozoic to avoid competition with dinosaurs (nocturnal bottleneck), [139] though, by the Middle Jurassic, they had branched out into several habitats—such as subterranean, arboreal, and aquatic— [140] and the largest known Mesozoic mammal ...
Artist's depiction of the end-Cretaceous impact eventSince the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era.
The North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals (or stages when referring to the rock strata of that age) and were established using geographic place names where ...
Multituberculates reached their peak diversity during the early Paleocene, shortly after the Cretaceous–Paleogene extinction event, but declined from the mid Paleocene onwards, likely due to competition with placental mammals such as rodents and ungulates, the group finally became extinct in the Late Eocene.
Land-mammal ages mostly represent intervals in the Cenozoic; they have not been proposed for the Mesozoic. However, related systems have been proposed for other periods of prehistory. Land-vertebrate "ages" (LVAs) based primarily on dinosaur faunas have been proposed for the late Cretaceous in western North America. [12]