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.
Allotheria is an extinct clade of mammals known from the Mesozoic and early Cenozoic. Shared characteristics of the group are the presence of lower molariform teeth equipped with longitudinal rows of cusps and enlarged incisors. Typically, the canine teeth are also lost. Allotheria includes Multituberculata, Gondwanatheria, and probably Haramiyida, although some studies have recovered haramiyidans to be basal mammaliaforms unrelated to multituberculates. Allotherians are often placed as crown group mammals, more closely related to living marsupials and placentals (Theria) than to monotremes or eutriconodonts, though some studies place the entirety of Allotheria outside of crown Mammalia.
Tribosphenida is a group (infralegion) of mammals that includes the ancestor of Hypomylos, Aegialodontia and Theria. It belongs to the group Zatheria. The current definition of Tribosphenida is more or less synonymous with Boreosphenida.
Castorocauda is an extinct, semi-aquatic, superficially otter-like genus of docodont mammaliaforms with one species, C. lutrasimilis. It is part of the Yanliao Biota, found in the Daohugou Beds of Inner Mongolia, China dating to the Middle to Late Jurassic. It was part of an explosive Middle Jurassic radiation of Mammaliaformes moving into diverse habitats and niches. Its discovery in 2006, along with the discovery of other unusual mammaliaforms, disproves the previous hypothesis of Mammaliaformes remaining evolutionarily stagnant until the extinction of the non-avian dinosaurs at the end of the Mesozoic.
Docodonta is an order of extinct Mesozoic mammaliaforms. They were among the most common mammaliaforms of their time, persisting from the Middle Jurassic to the Early Cretaceous across the continent of Laurasia. They are distinguished from other early mammaliaforms by their relatively complex molar teeth. Docodont teeth have been described as "pseudotribosphenic": a cusp on the inner half of the upper molar grinds into a basin on the front half of the lower molar, like a mortar-and-pestle. This is a case of convergent evolution with the tribosphenic teeth of therian mammals. There is much uncertainty for how docodont teeth developed from their simpler ancestors. Their closest relatives may have been certain Triassic "symmetrodonts", namely Woutersia, and Delsatia. The shuotheriids, another group of Jurassic mammaliaforms, also shared some dental characteristics with docodonts. One study has suggested that shuotheriids are closely related to docodonts, though others consider shuotheriids to be true mammals, perhaps related to monotremes.
Tritylodontidae is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, with several mammalian traits including erect limbs, endothermy, and some details of the skeleton. They were the last-known family of the non-mammaliaform synapsids, persisting into the Early Cretaceous.
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.
Haramiyida is a possibly paraphyletic order of mammaliaform cynodonts or mammals of controversial taxonomic affinites. Their teeth, which are by far the most common remains, resemble those of the multituberculates. However, based on Haramiyavia, the jaw is less derived; and at the level of evolution of earlier basal mammals like Morganucodon and Kuehneotherium, with a groove for ear ossicles on the dentary. Some authors have placed them in a clade with Multituberculata dubbed Allotheria within Mammalia. Other studies have disputed this and suggested the Haramiyida were not crown mammals, but were part of an earlier offshoot of mammaliaformes instead. It is also disputed whether the Late Triassic species are closely related to the Jurassic and Cretaceous members belonging to Euharamiyida/Eleutherodontida, as some phylogenetic studies recover the two groups as unrelated, recovering the Triassic haramiyidians as non-mammalian cynodonts, while recovering the Euharamiyida as crown-group mammals closely related to multituberculates.
Shuotherium is a fossil mammaliaform known from Middle-Late Jurassic of the Forest Marble Formation of England, and the Shaximiao Formation of Sichuan, China.
Shuotheriidae is a small family of Jurassic mammaliaforms whose remains are found in China, Great Britain and possibly Russia. They have been proposed to be close relatives of Australosphenida, together forming the clade Yinotheria. However, some studies suggest shuotheres are closer to therians than to monotremes, or that australosphenidans and therians are more closely related to each other than either are to shuotheres, with a 2024 study suggesting that shuotheriids were closely related to Docodonta outside of the Mammalia crown group.
The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period. It is known for its exceptionally preserved fossils, including those of plants, insects and vertebrates. It is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks. Previously, the Tiaojishan Formation was grouped together with the underlying Haifanggou Formation as a single "Lanqi Formation." The Tiaojishan Formation forms a key part of the Yanliao Biota assemblage, alongside the Haifanggou Formation.
The White Limestone Formation is a Bathonian geologic formation in the United Kingdom, dating to the Middle Jurassic, 168.3 to 166.1 million years ago. Fossil sauropod tracks have been reported from the formation. It is the lateral equivalent of the Blisworth Limestone. It predominantly consists of grey-yellow limestone, typically wackestone and packstone with subordinate ooidal grainstone. The Woodeaton Quarry locality has yielded microvertebrates.
Arboroharamiya is an extinct genus of early mammal from the Middle Jurassic Tiaojishan Formation of Inner Mongolia, China. Arboroharamiya belongs to a group of mammaliaforms called Haramiyida. The type species Arboroharamiya jenkinsi was described in the journal Nature in 2013 alongside a description of the closely related haramiyidan Megaconus. Unlike Megaconus, which is thought to have been ground-dwelling, Arboroharamiya was arboreal. It has a long tail that might have been prehensile, and very long fingers. Based on the shape of its teeth, Arboroharamiya might have been an omnivore or a seed eater. Recent interpretations of its specimen suggest that it possessed patagia and was a glider.
Euharamiyida also known as Eleutherodontida, is clade of early mammals or mammal-like cynodonts from the Middle Jurassic to Early Cretaceous of Eurasia and possibly North America. The group is sometimes considered a sister group to Multituberculata, or part of an earlier divergence within the synapsid line. It is disputed whether or not they are related to the Haramiyids from the Late Triassic, such as Haramiyavia. The morphology of their teeth indicates that they were herbivorous or omnivorous. Some members of the group are known to be arboreal, including gliding forms similar to modern flying squirrels or colugos.
Agilodocodon was a genus of shrew-sized docodont from the Middle Jurassic, believed to be the earliest known tree-climbing mammaliaform. It contains one species, A. scansorius.
Theriimorpha is a clade of mammals defined as including all mammals more closely related to therians than to monotremes. Eutriconodonta is usually considered among the most basal members of this group, with other members more closely related to therians like Allotherians placed in the subclade Theriiformes, though Eutriconodonta has also been recovered as less closely related to therians than monotremes are in some analyses, placing them outside the crown group of Mammalia. The unusual Late Jurassic digging mammal Fruitafossor has also been suggested to be a basal theriimorph in some studies. The position of Allotheria within Theriimorpha is controversial. While many studies recover Allotheria within crown Mammalia as more closely related to therians than to monotreme as a member of the clade Theriiformes, some studies recover the group as outside of crown Mammalia.
Vilevolodon is an extinct, monotypic genus of volant, arboreal euharamiyids from the Oxfordian age of the Late Jurassic of China. The type species is Vilevolodon diplomylos. The genus name Vilevolodon references its gliding capabilities, Vilevol, while don is a common suffix for mammalian taxon titles. The species name diplomylos refers to the dual mortar-and-pestle occlusion of upper and lower molars observed in the holotype; diplo, mylos.
Maiopatagium is an extinct genus of gliding euharamiyids which existed in Asia during the Jurassic period. It possessed a patagium between its limbs and presumably had similar lifestyle to living flying squirrels and colugos. The type species is Maiopatagium furculiferum, which was described from the Tiaojishan Formation by Zhe-Xi Luo in 2017; it lived in what is now the Liaoning region of China during the late Jurassic .Maiopatagium and Vilevolodon, described concurrently, offer clues to the ways various synapsids have taken to the skies over evolutionary time scales. A second species, M. sibiricum, was described from the Bathonian aged Itat Formation in western Siberia, Russia in 2019
Fossiomanus is an extinct genus of tritylodontid mammaliamorphs from the Early Cretaceous of China. It includes one species, F. sinensis, which is known from a single nearly complete skeleton from the Aptian Jiufotang Formation. Features of its limbs and vertebrae indicate that Fossiomanus was adapted towards a fossorial lifestyle.
Kermackodon is a genus of extinct allotherian mammaliform, known from the Middle Jurassic of England. It combines features of multituberculates with those of euharamyidans. The remains of type species, K. multicuspis were collected from Kirtlington Quarry in Oxford, England, by a team lead from UCL led by Professor Kenneth Kermack after whom the taxon is named, from sediments of the Forest Marble Formation, dating to the Bathonian stage of the Middle Jurassic. The genus and species were named by Percy M. Butler and Jerry Hooker in 2005. The remains comprise a left upper molar (M2), a lower last premolar, initially considered a left but later considered more likely to be right (p4), and an incomplete non-last upper premolar. A second species, K. oxfordensis, from Kirtlington and also sediments of the White Limestone Formation at Woodeaton Quarry was assigned to the genus in 2022, originally placed in the separate genus Eleutherodon. A 2020 study considered it to be more closely related to mutlituberculates than to euharamiyidans, while the 2022 study considered it to be a member of Euharamiyida.
