Data from: Functional morphology and biomechanics of an ontogenetic series of the Triassic cynodont <em>Brasilodon quadrangularis</em> and bite performance in the sister taxon of Mammaliformes

The Santa Maria Supersequence in Brazil has yielded numerous cynodont species from the Late Triassic, including derived probainognathians, which are relevant for the understanding of the cynodont-mammal transition. One of these cynodonts is Brasilodon quadrangularis, considered to be the sister taxon to Mammaliaformes due to a suite of apomorphic features in the skull, dentition, and postcranium. Specimens referred to this species have been described in detail, representing different ontogenetic stages. However, we know little of the functional performance and skull mechanics of this species and how this relates to recent studies of cynodont-mammaliaform skull mechanics. Here, we use beam analysis and finite element analysis (FEA) to assess the function of the skulls of *Brasilodon and compare their functional performance to that of the early mammaliaforms Morganucodon and Kuehneotherium. The ontogenetic series of Brasilodon shows a trend of increasing overall jaw strength and resistance, potentially indicating a change in diet and feeding behaviour through ontogeny. Beam analysis suggests that this taxon is more similar in bite performance to Morganucodon than to Kuehneotherium, regarding jaw strength and torsion resistance. Additionally, one of the studied skulls (UFRGS-PV-1043-T) was chosen for digital restoration and muscular reconstruction to increase understanding of the jaw muscle modifications in the cynodont-mammal transition. The muscular reconstruction revealed that the relative force contributions of the temporalis and masseter muscles of the Brasilodon ontogenetic series are more similar to non-mammaliaform cynodonts, such as Chiniquodon, *than to mammaliaforms. Our results provide further insight into cranial musculoskeletal anatomy and biomechanics in derived non-mammaliaform cynodonts.