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Temporal range: Early Paleocene to Late Miocene, 63.3–11.1Ma 
Creodonts were an important group of carnivorous mammals from in the ecosystems of Africa, Eurasia and North America. In Oligocene Africa, they were the dominant predatory group. They competed with the Mesonychids and the Entelodonts and ultimately outlasted them by the start of the Oligocene and by the middle of the Miocene respectively, but lost ground to the carnivorans. The last genus went extinct , and carnivorans now occupy their ecological niches.
Evolution and taxonomy
Creodonts were traditionally considered ancestors to Carnivora, but are now considered to have shared a common ancestor. They share with the Carnivora the carnassial shear, a modification of teeth that evolved to slice meat in a manner like scissors and gave both orders the tools to dominate the niche. Some researchers argue that the creodonts represent a group of mammals of diverse biological ancestry that resemble one another via convergent evolution, rather than being the descendants of a single common ancestor. Their origins lie at least as far back as the late Cretaceous, though they did not radiate much until the Cenozoic. Creodonts were the dominant carnivorous mammals from , peaking in diversity and prevalence during the Eocene. By the mid Oligocene, Creodonts supplanted both the Mesonychids, and giant flightless predatory birds entirely in North America, Eurasia and Africa, and in turn, competed with their own relatives, the Carnivorans. The last genus, Dissopsalis, went extinct about .
The creodonts ranged across North America, Eurasia and Africa, in forms that resemble those of some modern carnivores. Amongst their number was Sarkastodon, one of the largest mammalian land predators of all time, weighing an estimated 800 kg. Their dominance over the early Carnivora, known as miacids, began to wane after . The creodonts survived until ; the last form, Dissopsalis, died out in Pakistan. Bears, cats, mustelids, hyenas, canids, such as wolves, and other Carnivora now occupy the former creodont niches.
It is not known exactly why the creodonts were replaced by Carnivora. It may be because of their smaller brains and their locomotion, which was somewhat less energy-efficient (especially while running). Their limb structure limited leg movement to a vertical plane, as in horses; they were unable to turn their wrists and forearms inward to trip, slash, or grab prey as modern carnivores can. Creodonts had to depend entirely on their jaws to capture prey, which may be why creodonts generally had a larger head size in relation to their bodies than carnivores of similar stature. The creodont lumbosacral spine was not arranged as efficiently for running as in Carnivora. The arrangement of the teeth was also somewhat different. In the miacids (as with the modern Carnivora), the last upper premolar and the first lower molar are the carnassials, allowing grinding teeth to be retained behind for feeding on non-meat foods (the Canidae are the closest modern analog to miacid dentition). In creodonts, the carnassials were further back—either the first upper and second lower molars, or the second upper and third lower molars. This committed them to eating meat almost exclusively. These limits may have created important disadvantages over millions of years.
In the most hypercarnivorous family of modern Carnivora, the Felidae, the second and third molars have disappeared completely, and the first upper molars behind the carnassials have become vestigial. Modern cats thus eat plant food only incidentally.
- Lambert, 162
- Sorkin, B. 2008: A biomechanical constraint on body mass in terrestrial mammalian predators. Lethaia, Vol. 41, pp. 333–347
- "The Elements of Geology". Globusz. Retrieved March 11, 2008.
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