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20-563: The Thomas Fork Formation is an Early Cretaceous ( Albian ) geologic formation in Wyoming . Fossil dinosaur eggs have been reported from the formation. The following fossils were reported from the formation: Early Cretaceous Proposals for the exact age of the Barremian–Aptian boundary ranged from 126 to 117 Ma until recently (as of 2019), but based on drillholes in Svalbard

40-404: A prehensile tail , the development of a capitular tail on the humerus, the loss of tooth replacement on the second and fifth 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

60-622: 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 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

80-531: 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 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:

100-625: Is by far the largest LIP in Earth's history. The Ontong Java Plateau today covers an area of 1,860,000 km . In the Indian Ocean another LIP began to form at c. 120 Ma, the Kerguelen Plateau – Broken Ridge , together covering 2,300,000 km . Another LIP on the Liaodong Peninsula , China, c.  131–117 Ma, lasted for 10 million years. It was the result of the subduction of

120-633: The Canada Basin in the Arctic Ocean. With the opening of the Labrador Sea , Greenland became a separate tectonic plate and Laurentia became North America . The Proto-Caribbean Sea continued to grow and the Paraná-Etendeka LIP began to break Africa into three pieces. The Falkland Plateau broke off from southern Africa at 132 Ma and Madagascar ceased to move independently c. 120 Ma. In

140-776: The Kula and Pacific plates, which was probably caused by a superplume . During the opening of the South Atlantic the Paraná–Etendeka LIP produced 1.5 million km of basalts and rhyolites , beginning 133 Ma and lasting for a million years. The opening of the Central Atlantic continued as the Mid-Atlantic Ridge spread north to separate the Iberian Peninsula from the banks of Newfoundland and to connect to

160-637: The Late Jurassic continued to persist. Angiosperms (flowering plants) appeared for the first time during the Early Cretaceous; Archaefructaceae , one of the oldest fossil families (124.6 Ma) was found in the Yixian Formation , China. This time also saw the evolution of the first members of the Neornithes (modern birds). Sinodelphys , a 125 Ma-old boreosphenidan mammal found in

180-757: The Panthalassic Ocean the Pacific Plate continued to grow; the Arctic Alaska-Chukotka terrane formed the Bering Strait. Continued rifting opened new basins in the Indian Ocean, separating India, Antarctica, and Australia. By 110 Ma the Mid-Atlantic Ridge reached south into the Proto-Caribbean and South Atlantic, effectively separating South America from Africa, and continued rifting in

200-748: 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

220-705: 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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240-590: The Prudhoe Bay Oil Field has been interpreted as being sourced from the Triassic Shublik Formation shale and carbonate, Lower Cretaceous highly radioactive zone shale, and Lower Jurassic Kingak Shale . [REDACTED] Geology portal [REDACTED] Palaeontology portal Metatheria Metatheria (from Greek μετά- , metá- 'changed' and θηρίον , thēríon 'beast'; lit.   ' changed beasts ' )

260-670: 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

280-782: The Late Cretaceous, including both Deltatheroida and Marsupialiformes, with fossils also known from Europe during this time. During 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

300-564: The Yixian Formation, China, is one of the oldest mammal fossils found. The fossil location indicates early mammals began to diversify from Asia during the Early Cretaceous. Sinodelphys was more closely related to metatherians (marsupials) than eutherians (placentals) and had feet adapted for climbing trees. Steropodon is the oldest monotreme (egg-lying mammal) discovered. It lived in Gondwana (now Australia) at 105 Ma. Oil in

320-464: The defining early Aptian Oceanic Anoxic Event 1a (OAE1a) was carbon isotope dated to 123.1±0.3 Ma, limiting the possible range for the boundary to c. 122–121 Ma. There is a possible link between this anoxic event and a series of Early Cretaceous large igneous provinces (LIP). The Ontong Java - Manihiki - Hikurangi large igneous province, emplaced in the South Pacific at c. 120 Ma,

340-528: 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

360-405: The lower 5th premolar has a "very trenchant" cristid obliqua/ectolophid. The permanent deciduous lower fifth premolars are molar like and were historically identified as 1st molars, with 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 )

380-589: The northern end completed the longitudinal extent of the Atlantic. In Panthalassa the Ontong-Java Mega-LIP resulted in the formation of new tectonic plates and in the Indian Ocean the Kerguelen LIP began to push India northward. During this time many new types of dinosaur appeared or came into prominence, including ceratopsians , spinosaurids , carcharodontosaurids and coelurosaurs , while survivors from

400-417: 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 a closer evolutionary relationship between marsupials and placentals than either has with the monotremes, as does most genetic and molecular evidence. The earliest possible known metatherian

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