Granular substrates ranging from silt to gravel cover much of the Earth’s land area, providing an important habitat for fossorial animals. Many of these animals use their heads to penetrate the substrate. Although there is considerable variation in head shape, how head shape affects fossorial locomotor performance in different granular substrates is poorly understood. Here, head shape variation for 152 species of fossorial lizards was quantified for head diameter, slope and pointiness of the snout. The force needed to penetrate different substrates was measured using 28 physical models spanning this evolved variation was constructed. Ten substrates were considered, ranging in particle size from 0.025 to 4mm in diameter and consisting of spherical or angular particles. Head shape evolved in a weakly correlated manner, with snouts that were gently sloped being blunter. There were also significant clade differences in head shape among fossorial lizards. Experiments with physical models showed that as head diameter increased, absolute penetration force increased but force normalized by cross-sectional area decreased. Penetration force decreased for snouts that tapered more gradually and were pointier. Larger and angular particles required higher penetration forces, although intermediate size spherical particles, consistent with coarse sand, required the lowest force. Particle size and head diameter effect were largest, indicating that fossorial burrowers should evolve narrow heads and bodies, and select relatively fine particles. However, variation in evolved head shapes and recorded penetration forces suggest that kinematics of fossorial movement are likely an important factor in explaining evolved diversity.

Head shape data were collected for 152 species of lizards from 500 preserved museum specimens. We provide these data as well as a pruned, ultrametricized phylogeny from Zhang & Wiens (2016).

Penetration force data were collected for four substrates and one physcial model of a lizard head for a range of container diameters and substrate depths to determine what container size and depth was needed to avoid edge effects.

Penetration force data were collected for five glass bead and four natural rock substrates using 28 physical models that varied in diameter, slope and pointiness, mimicking evolved variation in lizard heads. For each combingation of model and substrate, ten trials were collected.

Please see the methods of the published work for further details.

The datasets described here are provided in three Excel spreadsheets. Each spreadsheet has a readme worksheet explaining each varaible in each dataset. Each spreadsheet contains multiple worksheets providing various aspects of the data.