Three-dimensional (3D) tongue movements are central to performance of feeding functions by mammals and other tetrapods, but 3D tongue kinematics during feeding are poorly understood. Tongue kinematics were recorded during grape chewing by macaque primates using biplanar videoradiography. Complex shape changes in the tongue during chewing are dominated by a combination of flexion in the tongue’s sagittal planes and roll about its long axis. As hypothesized for humans, in macaques during tongue retraction the middle (molar region) of the tongue rolls to the chewing (working) side simultaneous with sagittal flexion, while the tongue tip flexes to the other (balancing) side. Twisting and flexion reach their maxima early in the fast close phase of chewing cycles, positioning the food bolus between the approaching teeth prior to the power stroke. Although 3D tongue kinematics undoubtedly vary with food type, the mechanical role of this movement—placing the food bolus on the post-canine teeth for breakdown—is likely to be a powerful constraint on tongue kinematics during this phase of the chewing cycle. The muscular drivers of these movements are likely to include a combination of intrinsic and extrinsic tongue muscles.

These data were collected using the University of Chicago XROMM Facility. All procedures were approved by the University of Chicago IACUC. Four adult rhesus macaques (Macaca mulatta) were observed in this study (Table 1). The animals were housed in an AAALAC-accredited animal facility, fed monkey biscuits and given daily enrichment. They were trained to feed while restrained in a radiolucent, acrylic primate chair. Monkeys C and H were trained to feed with their heads restrained, facilitating marker tracking, shortening recording durations, and reducing radiation exposure. The monkeys were fed red grapes (10-20 mm) and biplanar videoradiographic data were collected (technique: 90–100 kVp, 10–16 mA, 200 Hz, and with a 2–4 ms shutter speed). Data were processed using the XROMM workflow and custom R scripts. Analyses were conducted using custom R scripts, included here.

Please see the uploaded Readme.txt file.

Data notes:
Four macaque monkeys were fed red grapes as described in the associated manuscript. Kinematics data were collected using the XROMM workflow, and transformed into mandibular and cranial coordinate systems following Orsbon et al. 2020. Note that while these data include cycles other than chews, the associated code files filter the data to only look at chews on the side of interest for a given individual. Descriptions of the variable names within the data files are given in Feeding_Codebook_for_Dryad.csv.

Code usage:
This code was written in R (version 3.6.3) with dependencies on the following packages:
- circular (v. 0.4-93)
- cowplot (v. 1.0.0)
- tidyverse (v. 1.3.0)

The data must be arranged in a directory structure as follows for the code to run:
Project Directory/
data/ = (contents of Feilich_etal_2021_rawdata.zip)
code/ = (contents of Feilich_etal_2021_code.zip)

To run the analyses and generate figures, use the project directory as the working directory, and run the "FinalFigures.R". This script will source the other scripts in the code/ directory. The outputs of the data processing and analysis are generated as R objects entitled [animal name]_analysis, and [animal name]_summary in the R workspace. Circular statistics for each animal are output as [animal name]_stats.