Changes in climate and habitat

One 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.[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. Faunal overturn at 25.8 Ma is the basis for division of the Arikareean time period (30.5Ц19 Ma), and the Arikareen NALMA (North American Land-Mammal Ages), into the Monroecreekian period (29.5Ц25.8 Ma), and then the Harrisonian period (25.8Ц23.5 Ma).[4] У Why did these cat-like creatures die out in North America (while surviving in Eurasia) with no replacement by the true cats? Their fate may be owed to the same factors that created the diversity of herbivorous mammals, for most cats need forest or cover from which to hunt. In an increasingly open America the nimravids may have found themselves without an ecological perch to hunt from, particularly if the competition with dogs prevented them from colonising the savannas.[5] Ф Ecological succession is the observed process of change in the species structure of an ecological community over time. The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self-perpetuating as a climax community. It is a phenomenon or process by which an ecological community undergoes more or less orderly and predictable changes following disturbance or initia

colonization of new habitat. Succession may be initiated either by formation of new, unoccupied habitat (e.g., a lava flow or a severe landslide) or by some form of disturbance (e.g. fire, severe windthrow, logging) of an existing community. Succession that begins in new habitats, uninfluenced by pre-existing communities is called primary succession, whereas succession that follows disruption of a pre-existing community is called secondary succession. Succession was among the first theories advanced in ecology and the study of succession remains at the core of ecological science. Ecological succession was first documented in the Indiana Dunes of Northwest Indiana[1] which led to efforts to preserve the Indiana Dunes.[2][3] Exhibits on ecological succession are displayed in the Hour Glass, a museum in Ogden Dunes. The Geologic temperature record are changes in Earth's environment as determined from geologic evidence on multi-million to billion (109) year time scales. The study of past temperatures provides an important paleoenvironmental insight because it is a crucial component of the climate and oceanography of the time. Global cooling was a conjecture during the 1970s of imminent cooling of the Earth's surface and atmosphere along with a posited commencement of glaciation. This hypothesis had little support in the scientific community, but gained temporary popular attention due to a combination of a slight downward trend of temperatures from the 1940s to the early 1970s and press reports that did not accurately reflect the scientific understanding of ice age cycles. In contrast to the global cooling conjecture, the current scientific opinion on climate change is that the Earth has not durably cooled, but undergone global warming throughout the 20th century.