Tritylodontidae ("three-knob teeth", named after the shape of their

cheek teeth Cheek teeth or postcanines comprise the molar and premolar teeth in mammals. Cheek teeth are multicuspidate (having many folds or tubercles). Mammals have multicuspidate molars (three in placentals, four in marsupials, in each jaw quadrant) and ...

) is an extinct family of small to medium-sized, highly specialized

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

-like

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s, with several mammalian traits including erect limbs, endothermy, and some details of the skeleton. They were the last-known family of the non-

mammaliaform Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during the Late Triassic. It is defined a ...

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

s, persisting into the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

. Most tritylodontids are thought to have been

herbivorous A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat n ...

, feeding on

vegetation Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...

such as stems,

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

, and

root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...

s, although at least one may have had a more omnivorous diet. Tritylodontid fossils are found in the

Americas The Americas, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

, and

Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...

– they appear to have had an almost global distribution, including

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

Description

The skull of tritylodontids had a high

sagittal crest A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...

. They retained the primitive condition of the joint between the

quadrate bone The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids ( reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms up ...

of the skull and the articular bone of the lower jaw – the retention of the joint is one of the reasons they are technically regarded to not be mammals, but are instead non-mammalian

mammaliamorph Mammaliamorpha is a clade of cynodonts. It contains the clades Tritylodontidae and Mammaliaformes, as well as a few genera that do not belong to either of these groups. The family Tritheledontidae has also been placed in Mammaliamorpha by some ...

s. The back of the skull had huge zygomatic arches for the attachment of its large jaw

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s. They also had a very well-developed

secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves med ...

. The tritylodont dentition differed from that of most other cynodonts: They did not have

canine teeth In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed teeth. In the context of the upper jaw, they are also known as '' fangs''. They can appear more fl ...

, and the front pair of

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s were enlarged and were very similar to those of modern-day rodents. Tritylodontids had a large gap, called a

diastema A diastema (: diastemata, from Greek , 'space') is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition may be referred to ...

, that separated the incisors from their square-shaped cheek teeth. The cheek teeth in the upper jaw had three rows of cusps running along its length, with grooves in between. The lower teeth had two rows of cusps which fitted into the grooves in the upper teeth. The matching of the cusps allowed the teeth to occlude more precisely than in earlier cynodonts. It would grind its food between the teeth in somewhat the same way as a modern rodent, although tritylodontids had a palinal jaw stroke (front-to-back), unlike rodents which have a propalinal jaw stroke (back-to-front). The teeth were well suited for shredding plant matter; however, there is evidence that some tritylodontids had more

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

diets, much in the same vein as modern mammals with "herbivore dentitions" like modern

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include '' Neotoma'' (pack rats), '' Bandicota'' (bandicoo ...

s. Like mammaliaforms, tritylodontids had

epipubic bone Epipubic bones are a pair of bones projecting forward from the pelvic bones of modern marsupials, monotremes and fossil mammals like multituberculates, and even basal eutherians (the ancestors of placentals, who lack them). They first occur i ...

s, a possible

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

between both clades, and this suggests they may also have laid eggs like modern

monotremes Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...

, or produced undeveloped fetus-like young like modern

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

s. A recent ''Kayentatherium'' shows that they indeed produced undeveloped young, but at litter sizes much larger than any monotreme or marsupial, at around 38 perinates. Tritylodonts were active animals that were likely

warm-blooded Warm-blooded is a term referring to animal species whose bodies maintain a temperature higher than that of their environment. In particular, homeothermic species (including birds and mammals) maintain a stable body temperature by regulating ...

and possibly burrowed. The small early tritylodontid '' Oligokyphus'' has been compared to a

weasel Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets, and European mink. Members of this genus are small, active predators, with long and slend ...

mink Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...

, with a long, slim body and tail. In ''

Kayentatherium ''Kayentatherium'' is an extinct genus of tritylodontid cynodonts that lived during the Early Jurassic. It is one of two tritylodonts from the Kayenta Formation of northern Arizona, United States. ''Kayentatherium'' means "Kayenta Beast", and ...

'' the burrowing adaptations seen in the skeleton have been re-interpreted as possibly suggesting a semi-aquatic ecology.

Discovery

The first tritylodontid named was '' Stereognathus'', from teeth found in the Middle

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

Great Oolite Group The Great Oolite Group is a Middle Jurassic stratigraphic unit that outcrops in southern England. It consists of a complex set of marine deposits primarily mudstone and bioclastic ooidal and fine grained limestone, deposited in nearshore to ...

of England{{cite journal , vauthors = Charlesworth E , year = 1854 , title = {{grey, itle not cited , journal=Rept. Brit. Assoc. Liverpool Abstracts , volume = 80 {{cite journal , vauthors = Panciroli E, Walsh S, Fraser NC, Brusatte SL, Corfe I , year = 2017 , title = A reassessment of the postcanine dentition and systematics of the tritylodontid ''Stereognathus'' (Cynodontia, Tritylodontidae, Mammaliamorpha), from the Middle Jurassic of the United Kingdom , journal =

Journal of Vertebrate Paleontology The ''Journal of Vertebrate Paleontology'' is a bimonthly peer-reviewed scientific journal that was established in 1980 by Jiri Zidek (University of Oklahoma). It covers all aspects of vertebrate paleontology, including vertebrate origins, evolu ...

, volume=37 , issue=5 , page = e1351448 , doi = 10.1080/02724634.2017.1351448 , hdl = 10138/230155 , doi-access = free , bibcode = 2017JVPal..37E1448P , hdl-access = free and the family name was erected by Cope in 1884.{{cite journal , vauthors = Cope ED , year = 1884 , title = The Tertiary Marsupialia , journal =

American Naturalist ''The American Naturalist'' is the monthly peer-reviewed scientific journal of the American Society of Naturalists, whose purpose is "to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance th ...

, volume = 18 , issue = 7 , pages = 686–697 , doi = 10.1086/273711 , doi-access = free Shortly after, another tritylodontid was discovered in the Upper

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

rocks of South Africa.{{cite journal , vauthors = Owen R , author-link = Richard Owen , year = 1884 , title = On the skull and dentition of a Triassic mammal (''Tritylodon longaevus'') from South Africa , journal = Quarterly Journal of the Geological Society of London , volume = 40 , pages = 146–152 , doi = 10.1144/gsl.jgs.1884.40.01-04.07 , hdl = 2027/hvd.32044107348633 , s2cid = 131059991 , hdl-access = free In 2023 skulls and teeth from dozens of tritylodonts were discovered at

Lake Powell Lake Powell is a reservoir on the Colorado River in Utah and Arizona, United States. It is a major vacation destination visited by approximately two million people every year. It holds of water when full, second in the United States to only the ...

on the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

in the United States, with more discoveries expected which may help to understand the history and evolution of mammals.

Evolutionary history

Tritylodontids first appeared during the

Rhaetian The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...

, the last stage of the

, and were abundant during the

, with several records from the

. The records of the group are almost entirely confined to the Northern Hemisphere, with the only records outside this region being in the Early Jurassic of South Africa and Antarctica. '' Xenocretosuchus,'' '' Montirictus'' and '' Fossiomanus'' are the latest known tritylodontids, from the

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 125.77 Ma (million years ago) and 121.4 ± 1.0 Ma (Historically, this stage was placed at 129.4 million to approximately 125 million years ago) It is a ...

Aptian The Aptian is an age (geology), age in the geologic timescale or a stage (stratigraphy), stage in the stratigraphic column. It is a subdivision of the Early Cretaceous, Early or Lower Cretaceous epoch (geology), Epoch or series (stratigraphy), S ...

aged Ilek Formation of Siberia, Kuwajima Formation of Japan, and

Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...

of China respectively. The morphology of ''Fossiomanus'' indictates it had a specialised

fossorial A fossorial animal () is one that is adapted to digging and which lives primarily (but not solely) underground. Examples of fossorial vertebrates are Mole (animal), moles, badgers, naked mole-rats, meerkats, armadillos, wombats, and mole salamand ...

(burrowing) lifestyle.{{cite journal , last1=Mao , first1=Fangyuan, last2=Zhang , first2=Chi , last3=Liu , first3=Cunyu , last4=Meng , first4=Jin , date=April 2021 , title=Fossoriality and evolutionary development in two Cretaceous mammaliamorphs , journal=

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

, volume=592 , issue=7855 , pages=577–582 , doi=10.1038/s41586-021-03433-2 , pmid=33828300 , bibcode=2021Natur.592..577M , s2cid=233183060 , issn=1476-4687 , url=https://www.nature.com/articles/s41586-021-03433-2 , lang=en , url-access=subscription

Ecology

The tooth morphology suggests that tritylodonts were primarily herbivorous, tooth microwear analysis indicates that tritylodonts ate food with low to moderate abrasiveness, and may have also consumed invertebrates.{{cite journal , vauthors = Kalthoff DC, Schulz-Kornas E, Corfe I, Martin T, McLoughlin S, Schultz JA , date = 25 July 2019 , title = Complementary approaches to tooth wear analysis in Tritylodontidae (Synapsida, Mammaliamorpha) reveal a generalist diet , journal = PLoS One , volume = 14 , issue = 7 , page = e0220188 , pmid = 31344085 , pmc = 6658083 , doi = 10.1371/journal.pone.0220188 , doi-access = free , bibcode = 2019PLoSO..1420188K

Phylogeny

Because of their mammal-like appearance, tritylodontids were originally placed within Mammalia. Starting with the work of British paleontologist D.M.S. Watson in 1942, a close relationship was favored between tritylodontids and cynodonts. Watson and other paleontologists noted that tritylodontids lacked the

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

and

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

jaw articulation that was characteristic of early mammals. {{harvp, Haughton, Brink, 1954 were the first to classify tritylodontids within Cynodontia. Later studies identified close similarities between the teeth of tritylodontids and

traversodontids Traversodontidae is an extinct family (biology), family of herbivore, herbivorous cynodonts. Traversodonts were primarily Gondwanan, with many species known from Africa and South America. Recently, traversodonts have also been found from Europe a ...

, and tritylodontids were eventually thought to be descendants of traversodontids. Under this classification, which was widely accepted in the following decades, Tritylodontidae was previous considered to be part of Gomphodontia, a larger group within

Cynognathia Cynognathia ("dog jaw") is one of two major clades of cynodonts, the other being Probainognathia. Cynognathians included the large carnivorous genus '' Cynognathus'' and the herbivorous or omnivorous gomphodonts such as traversodontids. Cynogn ...

. The name Tritylodontoidea was previously used for the group, which traditionally included the families Diademodontidae, Trirachodontidae, Traversodontidae, and Tritylodontidae. More recently, tritylodontids have been reinterpreted as close relatives of mammals. Beginning with {{harvp, Kemp, 1983, Tritylodontidae has been proposed by numerous studies as a member of

Probainognathia Probainognathia is one of the two major subgroups of the clade Eucynodontia, the other being Cynognathia. The earliest forms were carnivorous and insectivorous, though some groups eventually also evolved herbivorous diets. The earliest and most b ...

, the cynodont group containing mammals and related taxa. Gomphodontia is still used for the cynognathian group containing traversodontids and is preferred over Tritylodontoidea now that tritylodontids are not part of it. A

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis performed by {{harvp, Liu, Olsen, 2010 places Tritylodontidae very closely to Mammalia, as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of the clade formed by

Brasilodontidae ''Brasilodon'' ("tooth from Brazil") is an extinct genus of small, mammal-like cynodonts that lived in what is now Brazil during the Norian age of the Late Triassic epoch, about 225.42 million years ago. While no complete skeletons have been foun ...

and Mammalia.{{cite journal , vauthors = Liu J, Olsen P , year = 2010 , title = The phylogenetic relationships of Eucynodontia (Amniota: Synapsida) , journal = Journal of Mammalian Evolution , volume = 17 , issue = 3 , pages = 151–176 , s2cid = 40871206 , doi = 10.1007/s10914-010-9136-8 {{harvp, Ruta, Botha-Brink, Mitchell, Benton, 2013's phylogenetic analysis which is partially based on {{harvp, Liu, Olsen, 2010 places Tritylodontidae in a more derived position than Brasilodontidae. Below is a

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

from this analysis.{{cite journal , vauthors = Ruta M, Botha-Brink J, Mitchell SA, Benton MJ , date = October 2013 , title = The radiation of cynodonts and the ground plan of mammalian morphological diversity , journal = Proceedings of the Royal Society B: Biological Sciences , volume = 280 , issue = 1769 , pages = 20131865 , pmid = 23986112 , pmc = 3768321 , doi = 10.1098/rspb.2013.1865 The exact position of Tritylodontidae in relation to Mammalia is still debated, but most researchers agree they are closely related, usually considering Tritylodontidae to be non-mammaliaform mammaliamorphs. {{clade, style=font-size:85%;line-height:85% , label1=

, 1={{clade , 1=''

Lumkuia ''Lumkuia'' is an extinct genus of cynodont, fossils of which have been found in the Cynognathus Assemblage Zone of the Beaufort Group in the South African Karoo Basin that date back to the early Middle Triassic. It contains a single species, ' ...

'' , 2={{clade , 1='' Ecteninion'' , 2={{clade , 1={{clade , 1=''

Aleodon ''Aleodon'' is an extinct genus of cynodonts that lived from the Middle to Late Triassic. Relatively few analyses have been conducted to identify the phylogenetic placement of ''Aleodon'', although some have placed it as a sister taxon to '' Chin ...

'' , 2='' Chiniquodon'' , 2={{clade , 1='' Probainognathus'' , 2={{clade , 1=''

Trucidocynodon ''Trucidocynodon'' is an extinct genus of ecteniniid cynodonts from the Upper Triassic (Carnian) of Brazil. It contains a single species, ''Trucidocynodon riograndensis''. Fossils of ''Trucidocynodon'' were discovered in outcrops of the Upper Sa ...

'' , 2={{clade , 1='' Therioherpeton'' , 2={{clade , label1=

Tritheledontidae Tritheledontidae, the tritheledontids or ictidosaurs, is an extinct family of small to medium-sized (about 10 to 20 cm long) cynodonts. They were highly mammal-like, specialized cynodonts, although they still retained a few reptile-like ...

, 1={{clade , 1=''

Riograndia ''Riograndia'' is an extinct genus of prozostrodontian cynodonts from the Late Triassic of Brazil. The type species, type and only species is ''Riograndia guaibensis'', named after the State of Rio Grande do Sul and Guaíba Basin, where it was di ...

'' , 2={{clade , 1={{clade , 1=''

Chaliminia ''Chaliminia'' is an extinct genus of tritheledontid cynodont from the Triassic Period of what is now Argentina. The type and only species is ''C. musteloides''. See also *List of therapsids This list of therapsids is an attempt to create a com ...

'' , 2=''

Elliotherium ''Elliotherium'' is an extinct genus of cynodonts which existed in South Africa during the upper Triassic period. The type species is ''Elliotherium kersteni'', named after the Elliot Formation The Elliot Formation is a geological formation a ...

'' , 2={{clade , 1=''

Diarthrognathus ''Diarthrognathus'' ("Two joint jaw") is an extinct genus of tritheledontid cynodonts, known from fossil evidence found in South Africa and first described in 1958 by A.W. Crompton.Rieppel, Olivier. Evolutionary Theory and the Creation Controver ...

'' , 2=''

Pachygenelus ''Pachygenelus'' is a genus of extinct cynodont. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic. The genus was named in 1913 on the basis of a partial lower jaw found from South Africa, with the ...

'' , 2={{clade , label1=

, 1={{clade , 1='' Brasilitherium'' , 2='' Brasilodon'' , 2={{clade , label1=Tritylodontidae , 1={{clade , 1='' Oligokyphus'' , 2={{clade , 1=''

'' , 2={{clade , 1='' Tritylodon'' , 2='' Bienotherium'' , label2=

Mammaliaformes Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during the Late Triassic. It is defined as ...

, 2={{clade , 1=''

Sinoconodon ''Sinoconodon'' is an extinct genus of mammaliamorphs that appears in the fossil record of the Lufeng Formation of China in the Sinemurian stage of the Early Jurassic period, about 193 million years ago. While sharing many plesiomorphic traits w ...

'' , 2=''

Morganucodon ''Morganucodon'' ("Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represent ...

Genera

*'' Bienotherium'' *'' Bienotheroides'' *'' Bocatherium'' *'' Dianzhongia'' *'' Dinnebitodon'' *'' Fossiomanus'' *''

'' *'' Lufengia'' *'' Montirictus'' *'' Nuurtherium'' *'' Oligokyphus'' *'' Polistodon'' *'' Saurodesmus''?{{cite journal , last1=Szczygielski , first1=T. , last2=van den Brandt , first2=M. J. , last3=Gaetano , first3=L. , last4=Dróżdż , first4=D. , year=2024 , title=''Saurodesmus robertsoni'' Seeley 1891—The oldest Scottish cynodont , journal= PLoS One , volume=19 , issue=5 , page=e0303973 , doi=10.1371/journal.pone.0303973 , doi-access=free , pmid=38809839 , pmc=11135747 *'' Shartegodon'' *'' Stereognathus'' *'' Tritylodon'' *'' Xenocretosuchus'' *'' Yuanotherium'' *'' Yunnanodon''

References

{{reflist, 25em {{Cynodontia, P. {{Taxonbar, from=Q134746 Prehistoric therapsid families Late Triassic first appearances Early Cretaceous extinctions Taxa named by Edward Drinker Cope