Boreoeutheria
Magnorder of mammals containing Laurasiatheria and Euarchontoglires
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With a few exceptions, male boreoeutherians have a scrotum, an ancestral feature of the clade. The sub-clade Scrotifera was named after this feature.
Etymology
The name of this magnorder comes from Ancient Greek words:
- Βορέας (Boreas) meaning 'north wind' or 'the North',
- εὐ- (eu-) meaning 'good', 'right', or 'true',
- and θηρίον (thēríon) meaning 'beast'.
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Boreoeutherian ancestor
The majority of earliest known fossils belonging to this group date to about 66 million years ago, shortly after the K-Pg extinction event, though molecular data suggest they may have originated earlier, during the Cretaceous period. This is further supported with the earliest dated species of the pan-euungulate genus Protungulatum (P. coombsi about 70.6 to 66.043 Ma., and P. gorgun about 70.6 to 63.8 Ma.), alongside pan-carnivoran species Altacreodus magnus (about 70.6 to 66.043 Ma.), periptychid species Paleoungulatum hooleyi (about 70.6 to 66.043 Ma.), and arctocyonid species Baioconodon nordicus (about 70.6 to 63.8 Ma.).
The common ancestor of Boreoeutheria lived between 107 and 90 million years ago. The concept of a boreoeutherian ancestor was first proposed in 2004 in the journal Genome Research. The paper's authors claimed that the genome sequence of the boreoeutherian ancestor could be computationally predicted with 98% accuracy, but would "take a few years and a lot of money". It is estimated to contain three billion base pairs.