Probainognathus meaning “progressive jaw” is an extinct genus of cynodonts that lived around 235 to 221.5 million years ago, during the Late Triassic in what is now Argentina.

The first specimens of Probainognathus jenseni were discovered in the Chañares Formation in La Rioja Province, Argentina, by a group headed by the Harvard collector James A. Jensen.

The specimens were collected 3 kilometres (1.9 mi) north of the terminus of the Rio Chañares at the Campo de Talampaya.

[1] The skull was broad in proportion to its length, the face was short and narrow, but its zygomatic region was relatively large, seemingly for jaw muscle attachment.

Likewise, the parietals had more depth, the occipital crest was higher, and the orbits were proportionately larger relative to the rest of its head.

Romer (1970) interpreted this socket as articulating with the dentary bone of the lower jaw, as seen in modern mammals and early mammaliaforms like Morganucodon.

[2] Phylogenetic analyses have generally found probainognathids to be early-diverging members of the clade Probainognathia, being closer to mammals than to the traversodontids and other cynognathians.

[16] When Probainognathus inhabited this area, it is thought to have been a lacustrine region within a rift basin that got a large influx of sedimentary debris and volcanic ash.

[16] Fossils of both young and adult specimens were found at this locale, and these are not limited to Probainognathus, but rather represent many taxa that fell victim to the event.

It has, subsequently, been suggested that this unusual distribution of specimens could be due to the death event leaving these animals stranded with no other place to go, perhaps along a waterfront of some kind.

Suggested events include a large outpouring of ash, lethal gas surges, or, more likely, volcanism-induced flooding.

Volcanic activity may have caused damming or other water diversion, which led to major widespread flooding in the area, and the death of Probainognathus and other tetrapods.

[16] Unfortunately, however, it remains uncertain whether volcanism was the direct cause of this major death event, or if it just aided in preservation after the fact.