Skull dimension measurements from two museum collections
We included detailed data on skull dimensions and body mass of S. araneus from two populations: Žofín, in the Novohradské hory mountain range (Czech Republic; 48.671838, 14.690402; new data) from the dry collection deposited at the Department of Zoology at the Charles University in Prague, which were collected from 1971 to 1977; and Białowieża National Park (Poland; 52.700000, 23.866667; Dechmann et al. 2017) at the Mammal Research Institute Polish Academy of Sciences. These specimens were collected in Białowieża National Park in 1946-1947, and also preserved dry. We used digital calipers (±0.01 mm) to obtain braincase height, from the tympanic rings to the dorsal surface of the braincase, skull length, from the anteriormost projection of incisor 1 to the occipital condyle, maximum braincase width, and lower mandible length, from the alveolus dentalis of the incisor to the coronoid process. We focused our analyses on braincase height as we had previously found it to show the greatest change in response to Dehnel’s Phenomenon (Lázaro et al. , 2017, 2018a).