18-605: Acristatherium yanensis is an extinct basal eutherian from the Early Cretaceous (early Aptian , about 125 million years ago ) Lujiatun Bed of the Yixian Formation . It was described on the basis of a single specimen ( holotype ) from Beipiao , Liaoning , China , by Yaoming Hu, Jin Meng, Chuankui Li, and Yuanqing Wang in 2010. The specimen comprises a partial skull , 25 mm (0.98 in) long. It appears to possess
36-426: A vestige of a septomaxilla, a feature only otherwise seen in nonmammalian therapsids . [REDACTED] [REDACTED] This article about a Cretaceous mammal is a stub . You can help Misplaced Pages by expanding it . Eutheria see text. Eutheria (from Greek εὐ- , eú- 'good, right' and θηρίον , thēríon 'beast'; lit. ' true beasts ' ), also called Pan-Placentalia ,
54-666: A basal eutherian clade as sister to the Atlantogenata. Xenarthra Afrotheria Laurasiatheria Euarchontoglires Phylogeny after Wang & Wang, 2023. Metatheria † Sinodelphys † Ambolestes † Acristatherium † Microtherulum † Cokotherium † Juramaia † Eomaia † Prokennalestes † Murtoilestes † Montanalestes † Daulestes † Ukhaatherium † Asioryctes † Kennalestes † Gypsonictops † Cimolestes † Zalambdalestes † Aspanlestes † Protungulatum † Eoungulatum † Leptictis Placentalia Below
72-547: A capitular tail on the humerus, the loss of tooth replacement on the 2nd and 5th premolars and the retention of decidious teeth on the lower fifth premolars, the lower canines outwardly diverge from each other, the angular process on the dentary is equal to or less than half the length of the ramus , the dentary has a posterior masseteric shelf, and the lower 5th premolar has a "very trenchant" cristid obliqua/ectolophid. The permanent deciduous lower 5th premolars are molar like and were historically identified as 1st molars, with
90-452: A closer evolutionary relationship between marsupials and placental mammals than either has with the monotremes, as does most genetic and molecular evidence. The earliest possible known metatherian is Sinodelphys szalayi , which lived in China during the Early Cretaceous around 125 million years ago (mya). This makes it a contemporary to some early eutherian species that have been found in
108-409: Is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives. It is one of two groups placed in the clade Theria alongside Eutheria , which contains the placentals. Remains of metatherians have been found on all of Earths continents. Distinctive characteristics ( synapomorphies ) of Metatheria include: a prehensile tail , the development of
126-448: Is a phylogeny from Gheerbrant & Teodori (2021): Eomaia Prokennalestes Murtoilestes Bobolestes Montanalestes Paranyctoides Sheikhdheilia Lainodon Alostera Eozhelestes Avitotherium Metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals . First proposed by Thomas Henry Huxley in 1880, it
144-407: 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
162-478: 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 sinensis has been dated at 161 million years ago from the early Late Jurassic ( Oxfordian ) of China. However some authors have considered Juramaia as a stem therian instead, and some sources have doubted
180-748: The Pliocene , as well as the Polydolopimorphia , which likely had a wide range of diets. Metatherians then declined in diversity in South America during the Late Eocene as well as the later Oligocene epoch. The oldest known Australian marsupials are from the early Eocene, and are thought to have arrived in the region after having dispersed via Antarctica from South America. During the Oligocene epoch, Australian metatherians radiated rapidly, which contributed most to
198-705: The Pliocene - Pleistocene as part of the Great American interchange ). Metatherians first arrived in Afro-Arabia during the Paleogene , probably from Europe, including the possible peradectoid Kasserinotherium from the Early Eocene of Tunisia and the herpetotheriid Peratherium africanum from the Early Oligocene of Egypt and Oman. The youngest African metatherian is the possible herpetotheriid Morotodon from
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#1732863190833216-670: The Cenozoic. The two major groups of Cenozoic Laurasian metatherians, the opossum-like herpetotheriids and peradectids persisted into the Miocene before becoming extinct, with the North American herpetotheriid Herpetotherium , the European herpetotheriid Amphiperatherium and the peradectids Siamoperadectes and Sinoperadectes from Asia being the youngest Laurasian non-marsupial metatherians (with marsupials invading North America during
234-646: The Late Cretaceous, metatherians were more diverse than eutherians in North America. Metatherians underwent a severe decline during the Cretaceous–Paleogene extinction event , more severe than that suffered by contemporary eutherians and multituberculates , and were slower to recover diversity. Morphological and species diversity of metatherians in Laurasia remained low in comparison to eutherians throughout
252-531: The abdomen during pregnancy, though epipubic bones are present in many 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
270-743: The dating of the specimen. Distinguishing features are: Eutheria (i.e. Placentalia sensu lato , Pan-Placentalia): Notes: 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
288-528: The late Early Miocene of Uganda . Metatherians arrived in South America from North America during the latest Cretaceous or Paleocene and underwent a major diversificiation, with South American metatherians including both the ancestors of extant marsupials as well as the extinct Sparassodonta , which were major predators in South American ecosystems during most of the Cenozoic , up until their extinction in
306-450: The same area. However, Bi et al. (2018) reinterpreted Sinodelphys as an early member of Eutheria. The oldest uncontested metatherians are now 110 million year old fossils from western North America. Metatherians were widespread in Asia and North America during the Late Cretaceous, including both Deltatheroida and Marsupialiformes, with fossils also known from Europe during this time. During
324-437: The third premolar found in basal therians being lost, leaving 4 premolars in the halves of each jaw. The relationships between the three extant divisions of mammals ( monotremes , marsupials, and placentals ) was long a matter of debate among taxonomists . Most morphological evidence comparing traits, such as the number and arrangement of teeth and the structure of the reproductive and waste elimination systems , favors
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