| Palaeoxonodon Temporal range: Bathonian ~ | |
|---|---|
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Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | † Amphitheriida |
| Family: | † Amphitheriidae |
| Genus: | † Palaeoxonodon Freeman, 1976 [1] |
| Species: | †P. ooliticus |
| Binomial name | |
| †Palaeoxonodon ooliticus Freeman, 1976 | |
| Synonyms | |
| |
Palaeoxonodon is an extinct genus of cladotherian mammal from the Middle Jurassic of England [1] and Scotland. [2] [3]
The first fossils of Palaeoxonodon ooliticus were found in the Kirtlington cement quarry, Oxfordshire, England. [1] This site was rich in Mesozoic mammal remains from the Bathonian Forest Marble Formation. Later, two more species of Palaeoxonodon were named from the same site, P. leesi and P. freemani. [4] All of these fossils were individual teeth.
However, a recent fossil recovered from the Kilmaluag Formation of Skye, Scotland comprised a lower jaw with five molar teeth, four premolars, a canine and one incisor present. [2] This more complete fossil suggests that the separate species previously named from England were in fact all the same species, P. ooliticus, and only appeared different due to their differing position along the tooth row. This was also the case for Kennetheridium leesi. [4]
Two dentaries have recently been described. [3]
Palaeoxonodon ooliticus, like most mammals in the Mesozoic, was relatively small. The most complete fossil jaw - from Scotland - measures 11.6mm, but does not include the very front or rear portions of the jaw. The living animal was probably around the size of a mouse and would have been insectivorous.
The teeth of Palaeoxondon have an elongate lower molar talonid, with hypoconid placed buccal to the midline of the crown, well-developed upper molar metacone and wing-like parastylar region. [2]
Palaeoxondon belongs in the order Amphitheriida, closely related to Dryolestida. They are among the earliest cladotherian mammals, which have their origins in the Middle Jurassic and consist of the descendants of the last common ancestor of Amphitheriida, Dryolestida, Peramurida and Zatheria (which includes modern Therian mammals). Recent phylogenetic studies indicate that Palaeoxonodon was a sister taxon of Amphitherium itself. [3]
Compared to its closest relatives, Palaeoxonodon has rather slender jaws. [3]
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.
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, Delsatia, and Tikitherium.
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.
Gobiconodon is an extinct genus of carnivorous mammals belonging to the family Gobiconodontidae. Undisputed records of Gobiconodon are restricted to the Early Cretaceous of Asia and North America, but isolated teeth attributed to the genus have also been described from formations in England and Morocco dating as far back as the Middle Jurassic. Species of Gobiconodon varied considerably in size, with G. ostromi, one of the larger species, being around the size of a modern Virginia opossum. Like other gobiconodontids, it possessed several speciations towards carnivory, such as shearing molariform teeth, large canine-like incisors and powerful jaw and forelimb musculature, indicating that it probably fed on vertebrate prey. Unusually among predatory mammals and other eutriconodonts, the lower canines were vestigial, with the first lower incisor pair having become massive and canine-like. Like the larger Repenomamus there might be some evidence of scavenging.
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.
Morganucodonta is an extinct order of basal Mammaliaformes, a group including crown-group mammals (Mammalia) and their close relatives. Their remains have been found in Southern Africa, Western Europe, North America, India and China. The morganucodontans were probably insectivorous and nocturnal, though like eutriconodonts some species attained large sizes and were carnivorous. Nocturnality is believed to have evolved in the earliest mammals in the Triassic as a specialisation that allowed them to exploit a safer, night-time niche, while most larger predators were likely to have been active during the day.
Dryolestidae is an extinct family of Mesozoic mammals, known from the Middle Jurassic to the Early Cretaceous of the North Hemisphere. The oldest known member, Anthracolestes, is known from the Middle Jurassic Itat Formation of Western Siberia, but most other representatives are known from the Late Jurassic of North America and the Late Jurassic and Early Cretaceous of Europe. Most members are only known from isolated teeth and jaw fragments. Like many other groups of early mammals, they are thought to have been insectivores. They are generally classified in Cladotheria, meaning that they are considered to be more closely related to marsupials and placentals than to monotremes. They are placed as part of the broader Dryolestida, which also includes the Paurodontidae, and also sometimes the South American-Antarctic Meridiolestida, which are often considered unrelated cladotherians. Dryolestidae taxon is not based on a phylogenetic definition, but instead on the possession of unequal roots for the molars of the lower jaw. Additionally, the clade is distinguished by hypsodonty in lower molars, and uneven labio-lingual height for the alveolar borders of the dentary.
Amphitheriidae is a family of Mesozoic mammals restricted to the Middle Jurassic of Britain, with indeterminate members also possibly known from the equivalently aged Itat Formation in Siberia and the Anoual Formation of Morocco. They were members of Cladotheria, more derived than members of Dryolestida, and forming a close relationship with Peramuridae. Amphitheriidae is the only family of the order Amphitheriida.
Shuotherium is a fossil mammaliaform known from Middle-Late Jurassic of the Forest Marble Formation of England, and the Shaximiao Formation of Sichuan, China.
Cladotheria is a clade of mammals. It contains modern therian mammals and several extinct groups, such as the "dryolestoids", amphitheriids and peramurids. The clade was named in 1975 by Malcolm McKenna. In 2002, it was defined as a node-based taxon containing "the common ancestor of dryolestids and living therians, plus all its descendants". A different, stem-based definition was given in 2013, in which Cladotheria contains all taxa that are closer to Mus musculus than to the "symmetrodont" Spalacotherium tricuspidens.
Amphilestes is a genus of extinct eutriconodont mammal from the Middle Jurassic of the United Kingdom. It was one of the first Mesozoic mammals discovered and described.
Donodontidae is an extinct family of cladotherian mammals known from the Late Jurassic and Early Cretaceous of North Africa. When originally named in 1991, Donodontidae was a monotypic family containing a single species: Donodon perscriptoris. In 2022, four more species were designated and placed within the family: Donodon minor, Stylodens amerrukensis, Anoualestes incidens, and Amazighodon orbis. All five species are endemic to the Ksar Metlili Formation of Morocco, which is dated to the Tithonian and Berriasian. Donodontid fossils are restricted to postcanine teeth and associated jaw fragments.
The Kilmaluag Formation is a Middle Jurassic geologic formation in Scotland. It was formerly known as the Ostracod Limestone for preserving an abundance of fossil freshwater/low salinity ostracods. Gastropods, bivalves, trace fossil burrows, and vertebrate fossil remains have also been recorded from the formation. Vertebrate fossils include fish, crocodylomorphs, mammals, small reptiles, amphibians, theropod and sauropod dinosaurs and pterosaurs.
Amphitherium is an extinct genus of stem cladotherian mammal that lived during the Middle Jurassic of England. It was one of the first Mesozoic mammals ever described. A recent phylogenetic study found it to be the sister taxon of Palaeoxonodon. It is found in the Forest Marble Formation and the Taynton Limestone Formation.
Triconodon is a genus of extinct mammal from the Early Cretaceous of England and France with two known species: T. mordax and T. averianovi. First described in 1859 by Richard Owen, it is the type genus for the order Triconodonta, a group of mammals characterised by their three-cusped (triconodont) molar teeth. Since then, this "simplistic" type of dentition has been understood to be either ancestral for mammals or else to have evolved multiple times, rendering "triconodonts" a paraphyletic or polyphyletic assemblage respectively, but several lineages of "triconodont" mammals do form a natural, monophyletic group, known as Eutriconodonta, of which Triconodon is indeed part of.
Borealestes is a genus of docodontan from the Middle Jurassic of Britain, first discovered on the Isle of Skye near the village of Elgol. It was the earliest mammaliaform from the Mesozoic found and named in Scotland. A second species and was later found in other Middle Jurassic sites in England, but is now shown to be a different genus. A new species, B. cuillinensis was named in 2021, also from Skye.
Wareolestes rex is a mammaliaform from the Middle Jurassic (Bathonian) rocks of England and Scotland. It was originally known from isolated teeth from England, before a more complete jaw with teeth was found in the Kilmaluag Formation of Skye, Scotland.
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.
Peramus is an extinct genus of cladotherian mammal. It lived in the Late Jurassic and Early Cretaceous of Europe and North Africa.
Dobunnodon its an extinct genus of docodont from the Middle Jurassic (Bathonian) Forest Marble Formation of England, first discovered in Oxfordshire near the village of Kirtlington. The type species, D. mussettae, was originally named as a species of Borealestes in 2003.
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