The Euarchonta are a proposedgrandorder of mammals containing four orders: the Scandentia or treeshrews, the Dermoptera or colugos, the extinct Plesiadapiformes, and the Primates. The term "Euarchonta" appeared in 1999, when molecular evidence suggested that the morphology-based Archonta should be trimmed down to excludeChiroptera. Further DNA sequence analyses supported the Euarchonta hypothesis. Despite multiple papers pointing out that some mitochondrial sequences showed unusual properties and were likely distorting the overall tree, and despite Waddellet al. showing near total congruence of mtDNA-based and nuclear-based trees when such sequences were excluded, some authors continued to produce misleading trees. A study investigating retrotransposonpresence/absence data has claimed strong support for Euarchonta. Some interpretations of the molecular data link Primates and Dermoptera in a clade known as Primatomorpha, which is the sister of Scandentia. In some, the Dermoptera are a member of the primates rather than a sister group. Other interpretations link the Dermoptera and Scandentia together in a group called Sundatheria as the sister group of the primates. Euarchonta and Glires together form the Euarchontoglires, one of the four Eutherianclades. The current hypothesis, based on molecular clock evidence, suggests that the Euarchonta arose in the Cretaceous period, about 88million years ago, and diverged 86.2 million years ago into the groups of tree shrews and Primatomorpha. The latter diverged prior to 79.6 million years into the orders of Primates and Dermoptera. The earliest fossil species often ascribed to Euarchonta dates to the early Paleocene, 65 million years ago, but it appears to have been a non-placental eutherian. Although it is known that Scandentia is one of the most basal Euarchontoglire clades, the exact phylogenetic position is not yet considered resolved, and it may be a sister of Glires, Primatomorpha or Dermoptera or to all other Euarchontoglires.
