Creodonta

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Creodonta Fossil range: Late Paleocene to Late Miocene
Hyaenodon gigas and H. mongoliensis
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Infraclass: Eutheria Superorder: Laurasiatheria Order: Creodonta (Cope, 1875)
Families
Hyaenodontidae Oxyaenidae

The creodonts are an extinct order of mammals that lived from the Paleocene to the Miocene epochs. They shared a common ancestor with carnivorans.

Creodonts were an important group of carnivorous mammals from 55 to 35 million years ago 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 8 MYA, and carnivorans now occupy their ecological niches.

Contents 1 Evolution and taxonomy 2 Habitat 3 Reasons for extinction 4 References 5 Footnotes

[edit] Evolution and taxonomy

Creodonts were considered ancestors to Carnivora, but are now considered to have shared a common ancestor further back. They share with the Carnivora the carnassial shear, scissor teeth that evolved to slice meat 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.^[1] Creodonts were the dominant carnivorous mammals from 55 to 35 MYA, peaking in diversity and prevalence during the Eocene.^[2] 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 Carnivorans. The last genus, Dissopsalis, went extinct about eight million years ago.

[edit] Habitat

The creodonts ranged across North America, Eurasia and Africa, in forms that resemble those of modern carnivores. Amongst their number was Megistotherium, which some argue was the largest mammalian land predator of all time, the size of a bison and with a skull twice as big as a tiger's. Megistotherium may have rivaled Andrewsarchus mongoliensis in size. Their dominance over the early Carnivora, known as miacids, began to wane after 35 MYA. The creodonts survived until 8 million years ago; 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.

[edit] Reasons for extinction

It is not known exactly why the Creodonts were replaced by Carnivora. It may be because of their smaller brains and locomotion which was somewhat less energy-efficient (especially while running) and mostly plantigrade.^[3] These subtle disadvantages may have been important over millions of years. 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 (and so in 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 first upper and second lower molars, or second upper and third lower molars. This committed them to eating meat almost exclusively.

In the most strictly carnivorous 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.

[edit] References

• The Velvet Claw: A Natural History of the Carnivores, David Macdonald, BBC Books, ISBN 0-563-20844-9

• David Lambert and the Diagram Group. The Field Guide to Prehistoric Life. New York: Facts on File Publications, 1985. ISBN 0-8160-1125-7

[edit] Footnotes