Eutheria

 ( Mammal Taxonomy ) 

Eutheria (from Ancient Greek εὐ- ( eú-), meaning "true, well", and θηρίον ( thēríon), meaning "beast", and thus, "true beasts"), also called Pan-Placentalia, is the clade consisting of Placentalia and all mammals that are more closely related to placentals than to .

Eutherians are distinguished from non-eutherians by various of the feet, ankles, jaws and teeth. All extant eutherians lack , which are present in all other living mammals (marsupials and ). This allows for expansion of the abdomen during pregnancy, though epipubic bones are present in a number of primitive eutherians. Eutheria was named in 1872 by Theodore Gill; in 1880, Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia.

The earliest unambiguous eutherians are known from the Early Cretaceous Yixian Formation of China, dating around 120 million years ago. Two tribosphenic mammals, Durlstodon and Durlstotherium from the Berriasian age (~145–140 million years ago) of the Early Cretaceous in southern England have also been suggested to represent early eutherians. Another possible eutherian species Juramaia has been dated at from the early Late Jurassic (Oxfordian) of China. However some authors have considered Juramaia as a stem instead, and some sources have doubted the dating of the specimen.

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Characteristics Distinguishing features are:

• an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones
• the joint between the first Metatarsal bones and the entocuneiform bone (the innermost of the three cuneiform bones) in the foot is offset farther back than the joint between the second metatarsal and middle cuneiform bones—in metatherians these joints are level with each other
• various features of jaws and teeth including: having three molars in the halves of each jaw, each upper canine having two roots, the paraconid on the last lower premolar is pronounced, the talonid region of the lower molars is narrower than the trigonid.

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Taxonomy Eutheria (i.e. Placentalia sensu lato, Pan-Placentalia):

(2026). 9783110341553, De Gruyter. ISBN 9783110341553

Michael J. Benton (2014). 9781118407554, John Wiley & Sons. ISBN 9781118407554

(2026). 9788020032157, Academia. ISBN 9788020032157

Kenneth D. Rose (2006). 9780801884726, JHU Press. ISBN 9780801884726

• incertae sedis:
• ?Family †Holoclemensiidae (often considered a basal )
• ?Genus † Hyotheridium
  (2026). 9781402069970, Springer Netherlands. . ISBN 9781402069970
• ?Genus † Endotherium
• Genus † Durlstodon
• Genus † Durlstotherium
• Genus † Microtherulum
• Genus † Sinodelphys
• Genus † Cokotherium
• Genus † Ambolestes
• Genus † Montanalestes
• Genus † Indoclemensia
• ?Family †Horolodectidae (might belong somewhere within Placentalia sensu stricto)
• ?Genus † Juramaia
• Genus † Eomaia
• Genus † Acristatherium
• Clade †Tamirtheria ? (monophyly disputed)
• Genus † Prokennalestes
• ?Genus † Hovurlestes
• Genus † Murtoilestes
• Genus † Bobolestes (inclusive of the former genus Otlestes)
• Family †Adapisoriculidae (inclusive of the genus † Sahnitherium)
• Genus † Paranyctoides
• Family †Zhelestidae (inclusive of the genus Eozhelestes)
• Family †Cimolestidae (inclusive of the genera † Maelestes and † Batodon)
• Order †Asioryctitheria
• Family †Zalambdalestidae
• Order †Leptictida
• ?Order †Taeniodonta
• ?Family †Didymoconidae
• ?Genus † Purgatorius
• ?Genus † Protungulatum
• ?Genus † Oxyprimus
• Infraclass Placentalia sensu stricto

Notes:

• Some older systems contained an order called Cimolesta ( sensu lato), which contains the above taxa Cimolestidae, Taeniodonta and Didymoconidae, but also (some or all of) the taxa †Ptolemaiidae, †Palaeoryctidae, †Wyolestidae, †Pantolesta, †Tillodontia, †Apatotheria, †Pantodonta, Pholidota and †Palaeanodonta. Those additional taxa (which are usually considered members of Placentalia sensu stricto) were thus also placed next to Cimolestidae, now classified as basal Eutheria. Creodonta and Dinocerata have also been suggested as basal eutherians.
• Some authors classify the taxa placed at the end of the above system as part of Placentalia sensu stricto. Depending on the author, this applies to taxa placed from (and inclusive of) Leptictida or Asioryctitheria or Adapisoriculidae down to (and inclusive of) Oxyprimus. Specifically, some older authors associated Cimolestidae with Ferae, Zalambdalestidae with Glires, Zhelestidae with Ungulata, and Leptictida and Adapisoriculidae with Lipotyphla or Archonta. All of these are now considered basal Eutheria.

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Evolutionary history Eutheria contains several extinction genus as well as larger groups, many with complicated taxonomic histories still not fully understood. Members of the Adapisoriculidae, Cimolesta and Leptictida have been previously placed within the outdated placental group Insectivora, while Zhelestidae have been considered primitive .

Kenneth D. Rose (2026). 9780801892219, Johns Hopkins University Press. ISBN 9780801892219

However, more recent studies have suggested these enigmatic taxa represent crown group eutherians, more basal to Placentalia. Many non-placental eutherians are thought to have been , as is the case with many primitive mammals. However, the Zhelestidae are thought to have been herbivorous. Prior to the Cretaceous–Paleogene (K-Pg) extinction event, most eutherians were small and exhibited low anatomical and ecological diversity. Fossil evidence shows that the K-Pg extinction event led to a widespread increase in mammalian size and morphological diversity, with many small and medium-sized species going extinct and the surviving lineages evolving to have larger body sizes. Studies suggest that this overall increase in eutherian body size happened within a few hundred thousand years of the extinction. The extinction event also proved to be selective, as mammals with more generalized diets were more likely to survive than species with more specialized diets. In the early Paleocene, eutherians experienced an increase in taxonomic diversification, another result of the extinction event, leading to the evolution of the stem-primate Purgatorius, stem carnivorans Pristinictis and Ravenictis, and stem Proboscidea Eritherium. During this period, eutherians also expanded into new ecological roles, including specialized herbivores and carnivores. The Paleocene–Eocene Thermal Maximum further impacted eutherian morphological diversity, although the extent of its impacts is less studied.Emmerson, R. M. (2022). Changes in morphological disparity in eutherian mammals across the K–Pg boundary and Palaeocene–Eocene Thermal Maximum using discrete morphofunctional characters (MSc by Research thesis, University of Salford, UK). University of Salford Repository. https://salford-repository.worktribe.com/output/1330684/changes-in-morphological-disparity-in-eutherian-mammals-across-the-k-pg-boundary-and-palaeocene-eocene-thermal-maximum-using-discrete-morphofunctional-characters

The weakly favoured cladogram favours Boreoeutheria as a basal eutherian clade as sister to the Atlantogenata.

Phylogeny after Wang & Wang, 2023.

Below is a phylogeny from Gheerbrant & Teodori (2021):

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