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Prozostrodonts Temporal range: Late Triassic (Carnian), 233.23–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skull of Kayentatherium wellesi
Gaur
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Therapsida
Clade:	Cynodontia
Clade:	Probainognathia
Clade:	Prozostrodontia Liu and Olsen, 2010
Subgroups
†Agudotherium? †Alemoatherium †Santacruzgnathus †Therioherpeton †Prozostrodontidae †Prozostrodon †Pseudotherium †Dromatheriidae †Tritheledontidae Mammaliamorpha

Prozostrodontia is a clade of cynodonts including mammaliaforms and their closest relatives such as Tritheledontidae and Tritylodontidae. It was erected as a node-based taxon by Liu and Olsen (2010) and defined as the least inclusive clade containing Prozostrodon brasiliensis, Tritylodon langaevus, Pachygenelus monus, and Mus musculus (the house mouse). Prozostrodontia is diagnosed by several characters, including:

• Reduced prefrontal and postorbital bones, with the disappearance of a strut of bone called the postorbital bar separating the eye socket from the temporal region
• Unfused symphysis between the dentary bones in the lower jaw
• The presence of a small hole within the eye socket called the sphenopalatine foramen
• A long sagittal crest extending to the rearmost part of the lambdoidal crest at the back of the skull
• Neural spines of the dorsal vertebrae angled backward
• A convex-shaped iliac crest and a reduced posterior iliac spine on the hip
• An acetabular notch on the ischium (a groove in the hip socket)
• The position of a small projection called the lesser trochanter close to the head of the femur

Prozostrodontia includes tritylodontids, which have traditionally been placed within the more primitive cynodont group Cynognathia as distant mammal relatives. It also includes Tritheledontidae, which has long been placed close to mammals. Most previous studies considered Tritheledontidae a valid monophyletic grouping, meaning it was a true clade including all the descendants of a single common ancestor, but Liu and Olsen (2010) found Tritheledontidae to be a paraphyletic series of basal prozostrodontians. Below is a cladogram from Liu and Olsen (2010) showing the phylogenetic position of Prozostrodontia:

References

1. Martinelli, A. G.; Eltink, E.; Da-Rosa, Á. A. S.; Langer, M. C. (2017). "A new cynodont from the Santa Maria formation, south Brazil, improves Late Triassic probainognathian diversity". Papers in Palaeontology. 3 (3): 401–423. Bibcode:2017PPal....3..401M. doi:10.1002/spp2.1081.
2. Stefanello, M.; Martinelli, A. G.; Müller, R. T.; Dias-da-Silva, S.; Kerber, L. (2023). "A complete skull of a stem mammal from the Late Triassic of Brazil illuminates the early evolution of prozostrodontian cynodonts". Journal of Mammalian Evolution. 30 (2): 299–317. doi:10.1007/s10914-022-09648-y.
3. ^ Liu, J.; Olsen, P. (2010). "The Phylogenetic Relationships of Eucynodontia (Amniota: Synapsida)". Journal of Mammalian Evolution. 17 (3): 151. doi:10.1007/s10914-010-9136-8.

v t e Cynodontia
Kingdom: Animalia Phylum: Chordata Clade: Synapsida Clade: Therapsida Clade: Eutheriodontia Synapsida see Synapsida Cynodontia see below↓
Cynodontia Cynodontia †Dvinia †Nanocynodon †Madysaurus †Uralocynodon †Charassognathidae Abdalodon Charassognathus Nshimbodon †Procynosuchidae Procynosuchus Sludica Epicynodontia †Bolotridon †Cynosaurus †Nanictosaurus †Nythosaurus †Platycraniellus †Thrinaxodon †Vetusodon †Galesauridae Galesaurus Progalesaurus Eucynodontia †Kataigidodon †Cynognathia see Cynognathia Probainognathia see below↓
Probainognathia Probainognathia †Agudotherium †Candelariodon †Charruodon †Lumkuia †Protheriodon †Tessellatia †Chiniquodontidae Aleodon Chiniquodon Cromptodon? Riojanodon †Probainognathidae Bonacynodon Probainognathus †Ecteniniidae Diegocanis Ecteninion Trucidocynodon Prozostrodontia †Alemoatherium †Deccanodon †Dromatherium †Inditherium †Microconodon †Polonodon †Pseudotriconodon †Rewaconodon †Santacruzgnathus †Therioherpeton †Tricuspes †Prozostrodontidae Prozostrodon Pseudotherium †Tritheledontidae Chaliminia Diarthrognathus Elliotherium Irajatherium Pachygenelus Riograndia? Tritheledon Mammaliamorpha †Adelobasileus †Botucaraitherium †Brasilodon †Sinoconodon †Tikiodon †Tritylodontidae Bienotherium Bienotheroides Bocatherium Dianzhongia Dinnebitodon Fossiomanus Kayentatherium Lufengia Montirictus Nuurtherium Oligokyphus Polistodon Shartegodon Stereognathus Tritylodon Xenocretosuchus Yuanotherium Yunnanodon Mammaliaformes see below↓
Mammaliaformes Mammaliaformes †Bocaconodon †Brachyzostrodon †Bridetherium †Cherwellia †Cifellilestes †Delsatia †Dianoconodon †Dinnetherium †Dyskritodon †Eozostrodon †Erythrotherium †Gondwanadon †Hadrocodium †Hallautherium †Helvetiodon †Indotherium †Indozostrodon †Megazostrodon †Morganucodon †Paceyodon †Paikasigudodon †Purbeckodon †Rosierodon †Sinoconodon? †Storchodon †Stylidens †Wareolestes †Woutersia †Kuehneotheriidae Fluctuodon Kotatherium Kuehneon Kuehneotherium †Shuotheriidae Feredocodon Itatodon? Paritatodon? Pseudotribos Shuotherium †Docodonta Agilodocodon Borealestes Castorocauda Cyrtlatherium Dobunnodon Docodon Docofossor Dsungarodon Ergetiis Gondtherium? Haldanodon Hutegotherium Itatodon? Khorotherium Krusatodon Microdocodon Paritatodon? Peraiocynodon Sibirotherium Simpsonodon Tashkumyrodon Tegotherium †Haramiyida Avashishta? Hypsiprymnopsis? Haramiyavia Kalaallitkigun Kollikodon? Mojo? Theroteinus Thomasia Euharamiyida Allostaffia? Arboroharamiya Baidabatyr? Butlerodon Cryoharamiya Kermackodon? Maiopatagium Megaconus? Qishou Sharypovoia Shenshou Sineleutherus Vilevolodon Woodeatonia Xianshou Gondwanatheria? Hahnodontidae? Cifelliodon Denisodon Hahnodon Crown-Mammalia see Mammalia
See also Incertae sedis †Cistecynodon †Eoraetia †Gaumia †"Hahnia" †Kunminia †Lepagia †Meurthodon †Mitredon †Panchetocynodon †Redondagnathus †Saurodesmus? Paraphyletic / Polyphyletic groups Dromatheriidae Morganucodonta Symmetrodonta Triconodonta
Category

• Prozostrodontia
• Carnian first appearances
• Extant Late Triassic first appearances