Eutheria
Eutheria | |
---|---|
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.[1] However epipubic bones are present in some primitive eutherians.[2] Eutheria was named in 1872 by Theodore Gill; in 1880, Thomas Henry Huxley defined it to encompass a more broadly defined group than Placentalia.[3]
The oldest-known eutherian species is Juramaia sinensis, dated at 161 million years ago from the early Late Jurassic (Oxfordian) of China.[4] However, this early dating has been questioned, and Juramaia may originate from Early Cretaceous instead, which would make it contemporaneous to several other known eutherians.[5]
Characteristics
Distinguishing features are:
- an enlarged malleolus ("little hammer") at the bottom of the tibia, the larger of the two shin bones[6]
- 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[6]
- various features of jaws and teethtrigonid.[7]
Taxonomy
Eutheria (i.e. Placentalia sensu lato, Pan-Placentalia):[8][9][10][11][12][7][13][14][15][16][17][18][19][20][21][excessive citations]
- incertae sedis:
- ?Family †Holoclemensiidae[22] (often considered a basal metatherian)
- ?Genus †Hyotheridium[23][24]
- ?Genus †Endotherium[25]
- ?Genus †Durlstodon
- ?Genus †Durlstotherium
- Genus †Microtherulum
- Genus †Sinodelphys
- Genus †Cokotherium
- Genus †Ambolestes
- Genus †Montanalestes
- Genus †Indoclemensia[26]
- ?Family †Horolodectidae (might belong somewhere within Placentalia sensu stricto)[27]
- 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 †)
- ?Order †Taeniodonta[28]
- 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 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.[29] However, more recent studies have suggested these enigmatic taxa represent stem group eutherians, more basal to Placentalia.[30][31]
The weakly favoured cladogram favours Boreoeutheria as a basal eutherian clade as sister to the Atlantogenata.[32][33][34]
Phylogeny after Yang & Yang, 2023.[35]
Eutheria | |
Below is a phylogeny from Gheerbrant & Teodori (2021):[36]
Ecology
Many non-placental eutherians are thought to have been insectivores, as is the case with many primitive mammals.[37] However, the zhelestids are thought to have been herbivorous.[36]
References
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- ^ Archibald, J David. Eutheria (Placental Mammals) (PDF). San Diego, California: San Diego State University.
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- ^ "Eutheria". mv.helsinki.fi. 2018-02-27. Retrieved 2023-11-13.
- ^ "Palaeos Vertebrates: Archaic Mammals: Creodonts". Palaeos. Retrieved 2023-11-14.
- ISSN 0272-4634.
- ISBN 978-1-4020-6997-0. Retrieved 2023-11-13.
- ^ KIELAN-JAWOROWSKA, Z. (1975). "Evolution of the therian mammals in the Late Cretaceous of Asia. PART I. DELTATHERIDIIDAE (plates XXVIII-XXXV)" (PDF). Palaeontologia Polonica. 33 (10): 123, 124.
- ^ Wang, Y-Q; Kusuhashi, Nao; Jin, Xun; Chuan-kui, LI; Takeshi, SETOGUCHI; Chun-Ling, GAO; Jin-Yuan, LIU (2018). "Reappraisal of Endotherium niinomii Shikama, 1947, a eutherian mammal from the Lower Cretaceous Fuxin Formation, Fuxin-Jinzhou Basin, Liaoning, China". Vertebrata PalAsiatica.
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- ^ ISSN 1777-571X.
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