Eutheria

Distinguishing features are: • an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones{{cite journal • the joint between the first metatarsal bone 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. ==Taxonomy==

Eutheria (i.e. Placentalia sensu lato, Pan-Placentalia): • incertae sedis: • ?Family †Holoclemensiidae (often considered a basal metatherian) • ?Genus †Hyotheridium • ?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. ==Evolutionary history==

Eutheria contains several extinct genera 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 zhelestids have been considered primitive ungulates. However, more recent studies have suggested these enigmatic taxa represent stem group eutherians, more basal to Placentalia. Many non-placental eutherians are thought to have been insectivores, as is the case with many primitive mammals. However, the zhelestids 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 proboscidean 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. The weakly favoured cladogram favours Boreoeutheria as a basal eutherian clade as sister to the Atlantogenata. Phylogeny after Wang & Wang, 2023. }} }} }}}} }}}}}}}}}}}}}}}}}}}}}}}}|label2=Eutheria}} Below is a phylogeny from Gheerbrant & Teodori (2021): }}}}}} ==References==