Boreoeutheria (synonymous with Boreotheria) (from Greek Βορέας, Boreas "the greek god of north wind", εὐ-, eu- "good, right" and θηρίον, thēríon "beast" hence "northern true beasts") is a clade (magnorder) of placental mammals which is composed of the sister taxa Laurasiatheria (most hoofed mammals, most pawed carnivores, and several other groups) and Euarchontoglires (Supraprimates). It is now well supported by DNA sequence analyses, as well as retrotransposon presence or absence data. Placental mammals outside of this clade are the clades Xenarthra (sloths and their close relatives) and Afrotheria (elephants and their close relatives).
The earliest known fossils belonging to this group date to about 65 million years ago, shortly after the K-Pg extinction event, though molecular data suggest they may have originated earlier, during the Cretaceous period. With a few exceptions[a] male animals in the clade have a scrotum. The sub-clade Scrotifera was named after this feature.
The common ancestor of Boreoeutheria lived between 100 and 80 million years ago. The boreoeutherian ancestor gave rise to species as diverse as giraffes, dogs, mice, bats, whales, and humans. 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. Other studies have placed the common ancestor at closer to 65 million years ago.
- Magnorder Boreoeutheria
- Superorder Euarchontoglires (Supraprimates)
- Grandorder Euarchonta
- Grandorder Glires
- Superorder Laurasiatheria
- Order Eulipotyphla
- Order Cetartiodactyla: even-toed ungulates, including pigs, hippopotamus, camels, giraffe, deer, antelope, cattle, whales, dolphins, porpoises, etc.
- Suborder Tylopoda: camels and extinct relatives
- Suborder Suina: pigs, peccaries, and extinct relatives
- Suborder Ruminantia: cattle, sheep, goats, deer, antelope, etc.
- Suborder Whippomorpha: whales, dolphins, porpoises, and hippopotamuses
- Order Chiroptera: bats (cosmopolitan)
- Order Perissodactyla: odd-toed ungulates, including horses, donkeys, zebras, tapirs, rhinoceroses, and Chalicotheres (cosmopolitan)
- Clade Ferae
- Superorder Euarchontoglires (Supraprimates)
- Exceptional clades whose males lack the usual boreoeutherian scrotum are moles, hedgehogs, pangolins, some seals and walruses, rhinoceroses, tapirs, hippopotamuses, and cetaceans.
- While it is agreed that the cetaceans evolved within even-toed ungulates (Artiodactyla), much of the branching order within Laurasiatheria is not yet well resolved. In particular, the most difficult order to place definitively has been and still is Perissodactyla: Their proper place within or beside the Artiodactyls is controversial.
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- Drew, Liam (8 July 2013). "Why are testicles kept in a vulnerable dangling sac?". slate.com.
Between these branches, however, is where it gets interesting, for there are numerous groups, our descended but a-scrotal cousins, whose testes drop down away from the kidneys but don't exit the abdomen. Almost certainly, these animals evolved from ancestors whose testes were external, which means at some point they backtracked ... , evolving anew gonads inside the abdomen. They are a ragtag bunch including hedgehogs, moles, rhinos and tapirs, hippopotamuses, dolphins and whales, some seals and walruses, and scaly anteaters.
- Waddell; et al. (1999). "Using novel phylogenetic methods to evaluate mammalian mtDNA, including amino acid-invariant sites-LogDet plus site stripping, to detect internal conflicts in the data, with special reference to the positions of hedgehog, armadillo, and elephant". Systematic Biology. 48 (1): 31–53. doi:10.1080/106351599260427. PMID 12078643.
The name comes from the word scrotum, a pouch in which the testes permanently reside in the adult male. All members of the group have a postpenile scrotum, often prominently displayed, except for some aquatic forms and pangolins (which have the testes just below the skin). It appears to be an ancestral character for this group, yet other orders generally lack this as an ancestral feature, with the probable exception of Primates.
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