''Cynognathus'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of large-bodied cynodontian therapsids that lived in the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

. It is known from a single species, ''Cynognathus crateronotus''. ''Cynognathus'' was a

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

closely related to mammals and had a southern hemispheric distribution.

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s have so far been recovered from

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, and

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Description

''Cynognathus'' was a heavily built animal, and measured around in snout-to-vent body length and up to in total length. It had a particularly large head, up to in length, with wide jaws and sharp teeth. Its hindlimbs were placed directly beneath the body. There has been controversy about whether the forelimbs were also held upright or sprawled outwards in a reptilian fashion, but recent studies suggest

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

typically held their front legs in a posture between these two extremes. A study of living mammals concluded that "upright posture" in mammals is a myth based on the posture of mammal species specialized for fast running, such as dogs, hares, and antelopes; modern mammals that are not specialized for running often hold their forelimbs in a semi-sprawled posture. Possible autapomorphies of ''C. crateronotus'' include an extremely elongated postorbital bar and sectorial postcanine teeth with two serrated cusps distal to a recurved apex.

Discovery and naming

During 1888 and 1889, the British paleontologist Harry Govier Seeley visited southern Africa. In 1889, near Lady Frere, at a location where earlier Alfred Brown had discovered a tooth, Seeley excavated a skull and partial postcranial skeleton of a cynodontian. In 1894, Seeley named the genus ''Cynognathus'' with as

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''Cynognathus crateronotus''. Simultaneously, he named three other species in the genus: ''Cynognathus berryi'', honouring James Berry who had assisted in the excavations, ''Cynognathus platyceps'', the "flat jaw", and ''Cynognathus leptorhinus'', the "slender nose". The generic name ''Cynognathus'' is derived from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

''kyon'' and ''gnathos'', meaning "dog jaw". In 1895, Seeley published a more comprehensive description of these finds. Fossil material probably belonging to the genus has been given several different names over the years. Generic synonyms include ''Cynidiognathus'', ''Cynogomphius'', ''Karoomys'', ''Lycaenognathus'', ''Lycochampsa'' and ''Lycognathus''. Opinions vary as to whether all remains belong to the same species. The genus ''Karoomys'' is known only from a tiny juvenile. Species-level synonyms of ''Cynognathus crateronotus'' include ''Cynidiognathus broomi'', ''Cynidiognathus longiceps'', ''Cynidiognathus merenskyi'', ''Cynognathus berryi'', ''Cynognathus minor'', ''Cynognathus platyceps'', ''Cynogomphius berryi'', ''Karoomys browni'', ''Lycaenognathus platyceps'', ''Lycochampsa ferox'', ''Lycognathus ferox'', and ''Nythosaurus browni''.

Distribution

Fossils have been found in the Karoo, the Puesto Viejo Formation, Fremouw Formation, in

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and

. ''Cynognathus'' lived between the

Anisian In the geologic timescale, the Anisian is the lower stage (stratigraphy), stage or earliest geologic age, age of the Middle Triassic series (stratigraphy), series or geologic epoch, epoch and lasted from million years ago until million years ag ...

and the Ladinian (Middle Triassic). This genus forms a ''

Cynognathus Assemblage Zone The ''Cynognathus'' Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest Lithostratigraphy, lithostratigraphic Geological formation, formation in the Beauf ...

'' in the Beaufort Group of the Karoo Supergroup.

Classification

Seeley in 1894/1895 placed ''Cynognathus'' in a separate family Cynognathidae, within the Cynodontia. ''Cynognathus'' is presently the only recognized member of the family Cynognathidae. Later a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Cynognathia was named after the genus, within the Eucynodontia. ''Cynognathus crateronotus'' in 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 ...

after Stefanello ''et al''. (2023):

Paleobiology

In the Karoo Basin in what is now South Africa, ''Cynognathus'' lived in open environments with warm, dry summers and cool, wet winters, similar to today's Western Cape region but more arid. Individuals grew rapidly and continuously. Their hunting habits were largely unaffected by the changing seasons. 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 ...

was equipped with differentiated teeth, with fangs in the front for seizing prey and wider teeth in the rear of the jaw suitable for cutting meat; these show this animal could effectively process its food before swallowing. The presence of a

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 ...

in the mouth indicates that ''Cynognathus'' would have been able to breathe and swallow simultaneously. All these adaptations are consistent with maintaining a regular, high basal metabolic rate ("

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 ...

"), as in modern mammals. The possible lack of belly ribs, in the stomach region, suggests the presence of an efficient diaphragm, an important muscle that allows mammals to breathe equally well when they are walking, running, or holding still. Pits and canals on the bone of the snout indicate concentrations of

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s and blood vessels. In mammals, these structures support special sensory hairs ( whiskers), so it is likely ''Cynognathus'' had whiskers as well.

Description

Discovery and naming

Distribution

Classification

Paleobiology

See also

References

Further reading