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Scleromys sp. - jaws

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Description

fossil jaws fragment with teeth of rodent, mm 11 x 8.

The earliest fossil remains attributed to rodents date from the Paleocene (families Ischyromyidae and Paramyidae), although it is believed that the group has already developed during the Cretaceous, when the radiation could have occurred even lagomorphs. It ignores, however, from which group the rodents could have been down, even if the ancestor would be credited to some extinct species of the family of Zalambdalestidae.
From Laurasia, which would seem to have originated, the rodents spreading during the Eocene in Africa, where they underwent a remarkable adaptive radiation resulting in the emergence of most groups currently living.
From there, the ancestors of the current Caviomorpha (ie Istricognatha) reached South America during the early Oligocene, a period estimated at 31 million years ago, probably coming from Africa, then separated from the South American continent (which at the time was a huge island) by a stretch of sea is not too wide: arrived in South America, rodents found a small number of competitors such as ungulates and marsupials, and could therefore going to evolve to occupy ecological niches unusual, equivalent to those occupied by Artiodactyla other continents. When he joined North and South America, rodents of the two continents participated in the Great American Exchange, with Myomorpha who migrated to the south and the north who settled Caviomorpha.
The colonization of Australia, however, has been implemented several times in a period between 10 and 5 million years ago, giving the animals time to evolve into forms endemic despite competing with native marsupials before the arrival of humans and other introduced rodents in its wake.

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