Brain drain: exceptional pattern of calvarial venation in pangolins and its phylogenetic significance for Ferae

Abstract

The repeated failure of morphological phylogenetics to recover topologies congruent with molecular data in the interordinal diversification of placental mammals has become an iconic example of the challenges inherent in deep-time evolutionary reconstruction. This situation impedes the reliable placement of extinct taxa and stems, in part, from the underutilization of potentially informative morphological features. Diploic veins are a key example of such neglected structures, in that their diversity remains largely unexplored. Using microcomputed tomography scans and histology, this study investigates the phylogenetic signal of the diploic venous system across a broad spectrum of extant and extinct placental species. Our analysis reveals an exceptionally dense network of diploic venous channels in pangolins, contrasting sharply with the sparse development observed in most other placentals. Notably, a pattern similar to pangolins, albeit less pronounced, is present in many carnivorans and their extinct relatives. These discoveries could establish diploic veins as a powerful phylogenetic marker, unveiling a distinctive signature for Pholidota and suggesting a previously elusive synapomorphy for the Ferae clade. Comparisons with human cases of sinus hypoplasia further suggest that diploic veins play a major role in pangolin cerebral drainage and highlight a likely compensating mechanism involving these vessels and the superior sagittal sinus.