Cynognathus

Cynognathus is an extinct genus of large-bodied cynodontian therapsids that lived in the Middle Triassic. It is known from a single species, Cynognathus crateronotus. "Cynognathus" was a long predator closely related to mammals and had a southern hemispheric distribution. Fossils have so far been recovered from South Africa, Argentina, Antarctica, and Namibia.
Description.
"Cynognathus" was a heavily built animal, and measured around in snout-to-vent body 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, but the forelimbs sprawled outwards in a more reptilian fashion. This form of double (erect/sprawling) gait is also found in some primitive mammals alive today.
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 "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 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 "Cistecynodon", "Cynidiognathus", "Cynogomphius", "Karoomys", "Lycaenognathus", "Lycochampsa" and "Lycognathus". Opinions vary as to whether all remains belong to the same species. The genera "Karoomys" and "Cistecynodon" are known only from tiny juveniles. Species-level synonyms of "Cynognathus crateronotus" include "Cistecynodon parvus", "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 South Africa/Lesotho, Argentina and Antarctica.
"Cynognathus" lived between the Anisian and the Ladinian (Middle Triassic).
This genus forms a "Cynognathus Assemblage Zone" 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 Cynognathia was named after the genus, within the Eucynodontia.
Paleobiology.
The dentary was equipped with differentiated teeth that show this animal could effectively process its food before swallowing. The presence of a secondary palate in the mouth indicates that "Cynognathus" would have been able to breathe and swallow simultaneously.
The possible lack of belly ribs, in the stomach region, suggests the presence of an efficient diaphragm: an important muscle for mammalian breathing. Pits and canals on the bone of the snout indicate concentrations of nerves and blood vessels. In mammals, such structures allow hairs (whiskers) to be used as sensory organs.