The movement of limbless terrestrial animals differs fundamentally from that of limbed animals, yet few scaling studies of their locomotor kinematics and morphology are available. We examined scaling and relations of morphology and locomotion in sidewinder rattlesnakes (Crotalus cerastes). During sidewinding locomotion, a snake lifts sections of its body up and forward while other sections maintain static ground contact. We used high-speed video to quantify whole-animal speed and acceleration; the height to which body sections are lifted; and the frequency, wavelength, amplitude, and skew angle (degree of tilting) of the body wave. Kinematic variables were not sexually dimorphic, and most did not deviate from isometry, except wave amplitude. Larger sidewinders were not faster, contrary to many results from limbed terrestrial animals. Free from the need to maintain dynamic similarity (because their locomotion is dominated by friction rather than inertia), limbless species may have greater freedom to modulate speed independently of body size. Path analysis supported: (1) a hypothesized relationship between body width and wavelength, indicating that stouter sidewinders form looser curves; (2) a strong relationship between cycle frequency and whole-animal speed; and (3) weaker effects of wavelength (positive) and amplitude (negative) on speed. We suggest that sidewinding snakes may face a limit on stride length (to which amplitude and wavelength both contribute), beyond which they sacrifice stability. Thus, increasing frequency may be the best way to increase speed. Finally, frequency and skew angle were correlated, a result that deserves future study from the standpoint of both kinematics and physiology.

Full details on data collection and processing can be found in the Methods section of the published article.

Methods overview:

We measured morphometric and meristic traits for sidewinder rattlesnakes (Crotalus cerastes) captured at the Barry M. Goldwater Range near Yuma, Arizona, USA during June and July 2016. We then used two high-speed video cameras to record locomotor trials for for 66 individuals. We digitized a subset of videos using using the MATLAB programs DLTcal5 and DLTdv5 (Hedrick, 2008), choosing that subset based on trial quality (whether the snake performed multiple sidewinding cycles without stopping and turning), video and calibration quality, and representation of snakes from the entire size range of both sexes. We smoothed the data and extracted kinematic variables using custom MATLAB programs written by co-author BMS. The final sample for kinematic analysis included one representative trial for each of 26 individuals.

The morphology dataset includes 74 individuals, a subset of which are included in the kinematic dataset. It has some missing values for four individuals. File name: Tingle_et_al_2022_1_morphology.csv

The file of kinematic data output from the authors' custom MATLAB programs includes multiple trials per individual. Some of those trials have missing data. We ultimately chose one representative trial for each individual for statistical analayses, based on completeness of data and number of sidewinding cycles completed without stopping or turning. File name: Tingle_et_al_2022_2_kinematics_sand_2.0b.csv

The cleaned up data file of representative trials with their associated morphological measurements includes some outlier values that were removed prior to statistical analyses (see published article for details). File name: Tingle_et_al_2022_3_full_data_representative_trials_1.csv

The DLTdv5 output files include all output for all trials that were digitized, some of which were ultimately discarded (four files per trial; 344 files total). The *_xyzpts.csv files are the ones that were processed in the author's custom MATLAB programs. File names: Tingle_et_al_2022_4_DLTdv5_output_*.csv