Exaeretodon

Description

This genus was an herbivore up to 1.8 m long, with a specialized grinding action when feeding.

An analysis of the size of the bones of calves collected in Paleorrota concluded that the mother Exaeretodon had one or two calves, for one pregnancy.

Taxonomy

Exaeretodon is a gomphodontosuchine cynodont.

Despite the differences, a 2007 study concluded that the I. sudamericanus skull represents the same species as E. argentinus. Using allometry, paleontologist Jun Liu found I. sudamericanus to be the largest known example of a growth series in E. argentinus. Thus, Ischignathus is now regarded as a junior synonym of Exaeretodon. As the animal grew, the proportions of bones changed. These differing proportions were initially seen as species-distinguishing characters, but are now regarded as natural ontogenic variation.

Proexaeretodon vince was considered a synonym of Exaeretodon argentinus but was accepted as a valid taxon in 2023.

Phylogeny

Exaeretodon in a cladogram after Kammerer et al. (2012):

Palaeobiology

Dental microwear observed on four postcanine teeth of E. argentinus suggests that E. argentinus masticated by moving its jaws in a palinal motion.

Palaeoecology

Dental microwear evidence suggests that E. argentinus transitioned from utilising primarily crushing-based feeding in its early stages of development to primarily chewing-based feeding upon reaching adulthood. This suggests that juveniles of this species were to some degree faunivorous.

Palaeopathology

A pathological specimen of E. riograndensis has been found containing callouses in the ribs that correspond to a healed transverse fracture that likely occurred after a fall or an episode of intraspecific or interspecific combat. These injuries would have significantly impacted the individual's mobility such that it would have been unable to survive alone, suggesting that the gregariousness of the species helped this individual survive such a debilitating injury.

References

References

1. (May 2018). "U-Pb age constraints on dinosaur rise from south Brazil". Gondwana Research.
2. Liu, J.. (2007). "The taxonomy of the traversodontid cynodonts ''Exaeretodon'' and ''Ischignathus''". Revista Brasileira de Paleontologia.
3. (2023). "Old fossil findings in the Upper Triassic rocks of southern Brazil improve diversity of traversodontid cynodonts (Therapsida, Cynodontia)". The Anatomical Record.
4. (2012). "Ontogeny in the Malagasy Traversodontid Dadadon isaloi and a Reconsideration of its Phylogenetic Relationships". Fieldiana Life and Earth Sciences.
5. (29 November 2017). "Masticatory jaw movement of Exaeretodon argentinus (Therapsida: Cynodontia) inferred from its dental microwear". [[PLOS ONE]].
6. (21 October 2022). "Ontogenetic growth in the crania of Exaeretodon argentinus (Synapsida: Cynodontia) captures a dietary shift". [[PeerJ]].
7. (6 May 2025). "Bony injuries in a Late Triassic forerunner of mammals from Brazil". [[The Science of Nature]].