Fig. 3: Convergent evolution of the thylacine cranium.

a, Cranial phylomorphospace of 113 metatherian and eutherian taxa as estimated by principal component (PC) analysis, with the phylogeny in Supplementary Fig. 10 projected into shape space using squared-change parsimony. More than half of the total variance was contained in the first two components: PC1 describes shortening or lengthening of the face and jaws and relative height of the sagittal crest, while PC2 describes variation in skull width and snout shape (tubular versus blunt). The thylacine (blue star) displays striking cranial convergence with eutherian canids, falling closer in shape space to the red fox (Vulpes vulpes; shown) and grey wolf (Canis lupus) than to its own closest relatives. Using the pairwise distance measure C₁ ²³ on the full phenotypic dataset (PC1-31; 99% of the total shape variance), we estimate that approximately 34% of the ancestral phenotypic space between the thylacine and red fox has been closed by convergent evolution and 40% has been closed between the thylacine and grey wolf. These values are significantly greater than would be expected by chance (convratsig C₁, P < 0.05, n = 113). In contrast, the thylacine did not exhibit cranial convergence with other carnivorous marsupials or eutherian felids (Supplementary Table 7). b, Locations of 30 homologous landmarks used to compare cranial shapes shown in black (dorsal and lateral) and grey (ventral; expanded in Supplementary Fig. 5).