Biology:Eutheria

Short description: Clade of mammals in the subclass Theria

Further information: Biology:Evolution of mammals

Eutheria Temporal range: Late Jurassic–Holocene, 161–0 Ma PreЄ Є O S D C P T J K Pg N
Skeleton of Microtherulum, a basal eutherian from the Early Cretaceous of China
Northern treeshrew (Tupaia belangeri), a placental eutherian from Southeast Asia
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Theria
Clade:	Eutheria Gill, 1872
Subgroups
see text.

Eutheria (from Greek εὐ-, eú- 'good, right' and θηρίον, thēríon 'beast'; lit. true beasts), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials.

Eutherians are distinguished from noneutherians by various phenotypic traits of the feet, ankles, jaws and teeth. All extant eutherians lack epipubic bones, which are present in all other living mammals (marsupials and monotremes). This allows for expansion of the abdomen during pregnancy. However epipubic bones are present in some primitive eutherians.

The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the early Late Jurassic (Oxfordian) of China. However, this early dating has been questioned, and Juramaia may originate from Early Cretaceeous instead, which would make it contemporaneous to several other known 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.

Characteristics

The entocuneiform bone

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 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

Taxonomy

Eutheria [=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
  • 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 a †Batodon)
  • ?Order †Taeniodonta
  • Order †Asioryctitheria
  • Family †Zalambdalestidae
  • Order †Leptictida
  • ?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 (all or some of) the taxa †Ptolemaiidae, †Palaeoryctidae, †Wyolestidae, †Pantolesta (probably inclusive of the family †Horolodectidae), †Tillodontia, †Apatotheria, †Pantodonta, Pholidota and †Palaeanodonta. Those additional taxa (all of which are usually considered members of Placentalia sensu stricto today) were thus also placed among basal Eutheria in such older systems and were placed next to Cimolestidae.

-Some systems also included the †Creodonta and/or †Dinocerata as basal Eutherians.

-Some authors classify the taxa, which are at the end of the above system of basal Eutheria, as part of Placentalia sensu stricto. More specifically, depending on the author, this applies to the taxa of the above system that are placed from (and inclusive of) Leptictida or Asioryctitheria or Adapisoriculidae down to (and inclusive of) Oxyprimus.

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.

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

Eutheria	Atlantogenata   Xenarthra     Afrotheria     Boreoeutheria   Laurasiatheria     Euarchontoglires

Phylogeny after Yang & Yang, 2023.

	Metatheria
Eutheria	†Sinodelphys     †Ambolestes       †Acristatherium     †Microtherulum     †Cokotherium       †Juramaia       †Eomaia       †Prokennalestes       †Murtoilestes       †Montanalestes       †Daulestes         †Ukhaatherium       †Asioryctes     †Kennalestes             †Gypsonictops     †Cimolestes         †Zalambdalestes         †Aspanlestes       †Protungulatum     †Eoungulatum           †Leptictis     Placentalia

Ecology

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.

References

Wikidata ☰ Q17092469 entry