Multituberculata is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, and reached a peak diversity during the Late Cretaceous and Paleocene. They eventually declined from the mid-Paleocene onwards, disappearing from the known fossil record in the late Eocene. They are the most diverse order of Mesozoic mammals with more than 200 species known, ranging from mouse-sized to beaver-sized. These species occupied a diversity of ecological niches, ranging from burrow-dwelling to squirrel-like arborealism to jerboa-like hoppers. Multituberculates are usually placed as crown mammals outside either of the two main groups of living mammals—Theria, including placentals and marsupials, and Monotremata—but usually as closer to Theria than to monotremes. They are considered to be closely related to Euharamiyida and Gondwanatheria as part of Allotheria.
Placental mammals are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished from monotremes and marsupials in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young which are then nurtured for a period inside the mother's pouch. Placentalia represents the only living group within Eutheria, which contains all mammals more closely related to placentals than to marsupials.
Eomaia is a genus of extinct fossil mammals containing the single species Eomaia scansoria, discovered in rocks that were found in the Yixian Formation, Liaoning Province, China, and dated to the Barremian Age of the Lower Cretaceous about 125 million years ago. The single fossil specimen of this species is 10 centimetres (3.9 in) in length and virtually complete. An estimate of the body weight is 20–25 grams (0.71–0.88 oz). It is exceptionally well-preserved for a 125-million-year-old specimen. Although the fossil's skull is squashed flat, its teeth, tiny foot bones, cartilages and even its fur are visible.
Taeniolabis is a genus of extinct multituberculate mammal from the Paleocene of North America.
Eutheria, 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.
Kollikodon is an extinct species of mammal, considered to be an early monotreme. It is known only from an opalised dentary fragment, with one premolar and two molars in situ, as well as a referred maxillary fragment containing the last premolar and all four molars. The fossils were found in the Griman Creek Formation at Lightning Ridge, New South Wales, Australia, as was Steropodon. Kollikodon lived in the Late Cretaceous period, during the Cenomanian age.
Repenomamus is a genus of opossum- to badger-sized gobiconodontid mammal containing two species, Repenomamus robustus and Repenomamus giganticus. Both species are known from fossils found in China that date to the early Cretaceous period, about 125-123.2 million years ago. R. robustus is one of several Mesozoic mammals for which there is good evidence that it fed on vertebrates, including dinosaurs. Though it is not entirely clear whether or not these animals primarily hunted live dinosaurs or scavenged dead ones, evidence for the former is present in fossilized remains showcasing the results of what was most likely a predation attempt by R. robustus directed at a specimen of the dinosaur Psittacosaurus lujiatunensis. R. giganticus is among the largest mammals known from the Mesozoic era, only surpassed by Patagomaia.
Zalambdalestes is an extinct genus of eutherian mammal known from the Upper Cretaceous in Mongolia.
Cimolesta is an extinct order of non-placental eutherian mammals. Cimolestans had a wide variety of body shapes, dentition and lifestyles, though the majority of them were small to medium-sized general mammals that bore superficial resemblances to rodents, lagomorphs, mustelids, and marsupials.
Taeniodonta is an extinct order of eutherian mammals, that lived in North America and Europe from the late Cretaceous (Maastrichtian) to middle Eocene.
The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.
Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack et al. in 1973 as a replacement name for the paraphyletic Triconodonta.
Dryolestida is an extinct order of mammals, known from the Jurassic and Cretaceous. They are considered basal members of the clade Cladotheria, close to the ancestry of therian mammals. It is also believed that they developed a fully mammalian jaw and also had the three middle ear bones. Most members of the group, as with most Mesozoic mammals, are only known from fragmentary tooth and jaw remains.
Leptictida is a possibly paraphyletic extinct order of eutherian mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires, although they are more recently regarded as the first branch to split from basal eutherians. One recent large-scale cladistic analysis of eutherian mammals favored lepictidans as close to the placental crown-clade; and several other recent analyses that included data from Cretaceous non-eutherian mammals found Leptictis to belong to the superorder Afrotheria.
Megaconus is an extinct genus of allotherian mammal from the Middle Jurassic Tiaojishan Formation of Inner Mongolia, China. The type and only species, Megaconus mammaliaformis was first described in the journal Nature in 2013. Megaconus is thought to have been a herbivore that lived on the ground, having a similar posture to modern-day armadillos and rock hyraxes. Megaconus was in its initial description found to be member of a group called Haramiyida. A phylogenetic analysis published along its description suggested that haramiyidans originated before the appearance of true mammals, but in contrast, the later description of the haramiyidan Arboroharamiya in the same issue of Nature indicated that haramyidans were true mammals. If haramiyidans are not mammals, Megaconus would be one of the most basal ("primitive") mammaliaforms to possess fur, and an indicator that fur evolved in the ancestors of mammals and not the mammals themselves. However, later studies cast doubt on the euharamiyidan intrepretation, instead finding it to be a basal allotherian mammal.
Oxlestes is an extinct mammal from the Late Cretaceous of Asia, more specifically from the Cenomanian of Uzbekistan. A carnivorous species of uncertain affinities, it is notable for its relatively large size, being among the largest of all Mesozoic mammals. Due to the limited amount of material, it has been considered a nomen dubium.
Ukhaatherium is a now extinct species of mammal that lived during the upper Cretaceous about 84 to 72 million years ago in today's East Asia. It is known above all from the fossil locality Ukhaa Tolgod, Mongolia. An adult Ukhaatherium has an estimated weight of about 32g and bears several similarities to lipotyphlan insectivorans such as the tenrec.
Zhelestidae is a lineage of extinct eutherian mammals. Occurring in the Late Cretaceous from the Turonian to the Maastrichtian, they were an extremely successful group, with representatives present in Europe, Asia, India, Africa and North America, ostensibly rendering them a cosmopolitan clade. They were specialised towards an herbivorous lifestyle and were in fact initially considered stem-ungulates, but the presence of epipubics and "archaic" dental characters render them as non-placental eutherians.
Zalambdalestidae is a clade of Asian eutherians occurring during the Late Cretaceous. Once classified as Glires, features like epipubic bones and various cranial elements have identified these animals as outside of Placentalia, representing thus a specialised clade of non-placental eutherians without any living descendants, and potentially rather different from modern placentals in at least reproductive anatomy.
Ambolestes is an extinct genus of eutherian mammal from the Early Cretaceous of China. It includes a single species, Ambolestes zhoui, known from a single complete skeleton recovered from the Yixian Formation, part of the fossiliferous Jehol biota. Ambolestes is one of the most basal eutherians, presenting a combination of features from both early eutherians (stem-placentals) and early metatherians (stem-marsupials). This is responsible for the generic name of Ambolestes: "ambo" is Latin for "both", while "-lestes" is a popular suffix for fossil mammals. The species name honors influential Jehol paleontologist Zhou Zhonghe.
