Like most cynodonts, there is some evidence that they laid eggs, were warm blooded, as indicated by the detailed structure of the bones, and had a body covered by hair.

[7] The Middle Triassic Probainognathus and Massetognathus are the earliest non-mammalian cynodonts in the fossil record that show the initial steps of several phylogenetic transformations of the quadrate and can be characterized by several features: The rotation of the dorsal plate relative to the trochlea exhibits a progressively greater rotation more closely related to mammals, squamosal contact and medial expansion of the squamosal were crucial factors in the transforming the quadrate and the articulation of the cranium.

It had a higher skull and mandible, slightly dorsally pointed dentary ventral border under the coronoid process, and less post canines compared to the other three species.

[13] In 1967, American paleontologist Alfred Romer named three new species under the genus: Massetognathus pascuali, M. teruggi, and M. major during his expedition in western Argentina.

[9][12] In 1981, Brazilian paleontologist Mário Costa Barberena named the fourth species, Massetognathus ochagaviae on the basis of a specimen from the Santa Maria Formation in Brazil.

However, after collecting multiple skull samples, they clearly sorted into two size groups, rather than showing growth stages of a single species.

[5] Cynognathus Diademodon Trirachodon Cricodon Langbergia Andescynodon Pascualgnathus Arctotraversodon Boreogomphodon Nanogomphodon Massetognathus Dadadon Santacruzodon Gomphodontosuchus Menadon Protuberum Exaeretodon Scalenodontoides There are four upper and three lower triangular incisors of modest size with canines that are relatively less developed.

It has been established that Massetognathus with multi-cuspate post canines adapted to herbivory, moved the lower jaw posteriorly and dorsally during the power stroke of the occlusion.

Considering the abundance of the herbivorous cynodont Massetognathus, it is clear that this taxon represents the main food resource in the Chañares assemblage.

[7] The Chañares Formation, where Romer first discovered Massetognathus crops out in the Ischigualasto-Villa Union Basin, which is formed along the western margin of South America during the breakup of Gondwana.

[9][14] The Chañares Formation represented an extremely thick accumulation of volcanic tuffs that were deposited in wither eolian or lacustrine settings.

Ash-flow sheets potentially were emplaced as mass flows on sub alluvial surfaces and in lakes that occupied the Ischigualasto-Villa Únion Basin.

In the mass mortality event, there is a clear bias towards preservation of individuals representing smaller-sized to mid-sized taxa such as Massetognathus.

The mass mortality assemblage, with a large quantity of complete or partially articulated skeletons, shows some post-mortem sorting, followed by rapid burial that prevent the carcasses from being scavenged, crushed by species or exposed to weathering.