This sequence preserves a faunal association known as the Dinodontosaurus Assemblage Zone, which contains numerous other species of cynodonts, dicynodonts and reptiles.
They were both discovered in the 1940s by the Brazilian palaeontologist Llewellyn Ivor Price in two separate rocky outcrops (sangas) in the Pinheiros region, around 12 kilometres (7.5 mi) south of the town of Candelária, Rio Grande do Sul.
[1] The rocks belong to the Pinheiros-Chiniquá Sequence of the Santa Maria Supersequence, which has been dated to the Ladinian to early Carnian ages.
The first part of the generic name Bonacynodon is derived from the surname of José Bonaparte, an Argentine palaeontologist who specialised in the Mesozoic vertebrates of South America.
The specific epithet schultzi honours Cesar L. Schultz, a Brazilian palaeontologist and professor at the Federal University of Rio Grande do Sul.
As in the closely related Probainognathus, the palate ended in front of the last postcanine; this is somewhat shorter than what is seen in the more basal (early-diverging) chiniquodontids and the more derived (late-diverging) prozostrodonts.
A large basin called the masseteric fossa stretched from near the last postcanine to the tip of the coronoid process.
The canines had strongly serrated (saw-like) back edges, which is an autapomorphy (unique derived feature) of the taxon.
[1] When describing Bonacynodon, Martinelli and colleagues performed a phylogenetic analysis to find out its relationships to other cynodonts.
[4][5][6][7] Below is a cladogram following the analysis of Martinelli et al. (2016):[1] Ecteninion Chiniquodon Bonacynodon Probainognathus Protheriodon Prozostrodon Therioherpeton Tritheledontidae Tritylodontidae Botucaraitherium Brasilitherium Brasilodon Adelobasileus Sinoconodon Mammaliaformes Early-diverging probainognathians like the ecteniniids and Chiniquodon had postcanine teeth with strongly recurved (and in the case of the ecteniniids, even serrated) cusps, which would have been well-suited for a carnivorous diet.
The straight, unserrated postcanine cusps of probainognathids like Bonacynodon were more similar to those of basal prozostrodonts; this is thought to be an adaptation towards insectivory.
[1] Bonacynodon belongs to the Dinodontosaurus Assemblage Zone, the lowermost of the four biostratigraphic units of the Santa Maria Supersequence of the Paraná Basin.
[1] The Pinheiros-Chiniquá and Santa Cruz Sequences appear to have been deposited during a dry period, in which the landscape was dominated by loessic plains.
In addition to Bonacynodon, these include the probainognathians Aleodon, Candelariodon, Chiniquodon and Protheriodon, and the traversodontids Luangwa, Massetognathus, Protuberum, Scalenodon and Traversodon.
Other vertebrates from this Assemblage Zone include the dicynodonts Dinodontosaurus and Stahleckeria, the parareptile Candelaria, the rhynchosaur Brasinorhynchus, the enigmatic archosauriform Barberenasuchus, several species of pseudosuchians (the group that contains modern-day crocodilians and their extinct relatives), and the aphanosaur (primitive stem-bird) Spondylosoma.