Extinction risk varies across species and is influenced by key ecological parameters, such as diet specialization. For predictive conservation science to be effective, we need to understand extinction risk factors that may have implicated recent species extinctions. Diet and feeding behaviour of the large extinct marsupial carnivore Thylacinus cynocephalus or thylacine have long been debated. Improved understanding of the skull's biomechanical performance and its limitations in a comparative context may yield important insights. Here, we use three-dimensional (3D) finite element analysis to assess aspects of biomechanical performance in the skull of T. cynocephalus relative to those of two extant marsupial carnivores with known diets that occurred sympatrically with T. cynocephalus: the Tasmanian devil, Sarcophilus harrisii, and spotted-tailed quoll, Dasyurus maculatus. Together, these three species comprised the large mammalian carnivore guild in Tasmania at the time of European settlement. The bone-cracking S. harrisii produced high bite forces for its size as expected, but the stresses induced were surprisingly high. A higher proportion of cancellous bone in the skull of this osteophage may act to absorb shock but decrease rigidity and hence raise stress. A relatively high bite force and rigid skull characterized D. maculatus, which may allow them to target prey of variable sizes. Compared with S. harrisii and D. maculatus, we found that the skull of T. cynocephalus was least well adapted to withstand forces driven solely by its jaw-closing musculature, as well as to simulations of struggling prey. Our findings suggest that T. cynocephalus likely consumed smaller prey relative to its size, which may have had implications for their survival.