DOI: 10.5061/dryad.9kd51c5x8
title: Dental measures of extant lizards and fossil reptiles

description: Procolophonoids are hypothesized to be some of the first highly
 specialized herbivores to evolve in the aftermath of the end-Permian
 extinction. Hypotheses of procolophonoid diet are based on their unique
 dentitions: bulbous, multicuspid, differentiated teeth, specialized for
 feeding on fibrous plant matter. However, these conclusions are largely
 based on qualitative descriptions, and there has yet to be a broadscale,
 quantitative comparison of this group of fossil reptiles to modern ones.
 In our study, we use relatively simple measures of tooth shape and linear
 discriminant analysis (LDA) to predict dietary ecology from tooth
 dimensions and phylogenetic MANOVA to test for significant differences in
 tooth shape for different diets. We find that procolophonids are largely
 predicted as herbivorous but occupy different ecological niches from
 modern lizards and that simple methods return relatively similar results
 as complex methods. We hypothesize that the different mechanical
 challenges of Triassic-age flora produced a different 'kind' of
 herbivorous tooth from those observed in extant lizards, like those in
 procolophonids. 
description: # Dental measures of extant lizards and fossil reptiles Dataset DOI:
 [10.5061/dryad.9kd51c5x8](https://doi.org/10.5061/dryad.9kd51c5x8) ##
 Description of the data and file structure This dataset contains the data
 and analytical code underlying a comparative study of dental and cranial
 morphology in a group of fossil reptiles (procolophonids and close kin)
 and extant lizards. Our dataset  includes averaged datasets of dental
 measures for fossil procolophonids (`procolophonid_avgs.csv`) and living
 lizards (`extantlizard_avgs.csv`), an ultrametric phylogenetic tree of
 sampled lizard species (`ultrametric_lizardtree.newick`), two annotated R
 scripts implementing linear discriminant analyses and phylogenetic MANOVAs
 (`code_LDA.R`, `code_phylogenetic_MANOVA.R`), and a supplementary figure
 visualizing the relationship between head length and body size
 (`MartinezandJenkins_SuppFigure1.tiff`). We build a predictive model based
 on living lizards to quantitatively predict the diets of procolophonids
 using relatively simple measures of tooth shape and size. In our study, we
 use linear discriminant analysis (LDA) to separate differences in our
 extant data and use that to predict diet in fossils taxa. We also use
 phylogenetic multivariate analysis of variance (MANOVA) to understand the
 extent to which shared evolutionary history guides the differences between
 groups.  For 91 species of extant lizards, we measured and calculated
 species averages for the following dental measures using the last tooth in
 the tooth row: labiolingual width (W), mesiodistal length (L), tooth area
 (A), and length/width ratio (R). A well-known proxy for body size in
 reptiles, snout-vent length (SVL), was also included for extant lizards
 (obtained from the literature). Head length (HL) was also collected
 (obtained from specimens measured). Measures of size (L, W, A, HL, and
 SVL) were log-transformed before being incorporated into analyses. The
 same dental measures were collected for 24 fossil specimens (23
 procolophonoids + 1 nyctiphruretid). Because complete specimens are rare,
 SVL was not feasible to collect for fossil taxa. HL was collected instead
 (obtained from specimens measured or literature). A regression analysis of
 log-transformed HL on log-transformed SVL was performed to ensure that HL
 is a good predictor of overall body size for our sample.  ### Files and
 variables #### File: extantlizard_avgs.csv **Description:** Contains mean
 linear and area-based measurements for extant lizard species. Each row
 represents an individual species average derived from multiple specimens.
 ##### Variables * Species: taxonomic identification (genus and species). *
 Diet: categorical descriptor of predominant dietary type (e.g.,
 carnivorous, omnivorous, herbivorous); (based on Meiri, 2024).  *
 Length: average mesiodistal length of the last tooth in the tooth row
 (millimeters, mm). * Width: average labiolingual width of the last tooth
 in the tooth row (mm). * Ratio: ratio of mean tooth area to head length. *
 Area: calculated average surface area of individual teeth (mm²). *
 SVL: snout–vent length (mm), measured from snout tip to anterior margin of
 the cloaca. * Head_length: total head length measured from snout to
 occiput (mm). #### File: procolophonid_avgs.csv **Description:** Contains
 averaged cranial and dental measurements for fossil* *specimens. Each row
 represents the mean values for a species or individual specimen.
 Measurements include head length, tooth dimensions, and derived ratios.
 ##### Variables * Species: taxonomic identification of the specimen (genus
 and species, when available). * Length: average mesiodistal length of the
 last tooth in the tooth row (millimeters, mm). * Width: average
 labiolingual width of the last tooth in the tooth row (mm). * Ratio: ratio
 of mean tooth area to head length. * Area: calculated average surface area
 of individual teeth (mm²). * Head_length: total head length measured from
 snout to occiput (mm). #### File: ultrametric_lizardtree.newick
 **Description:** Time-calibrated ultrametric phylogenetic tree of extant
 lizard species included in the dataset `extantlizard_avgs.csv`. The tree
 topology is based on Pyron et al. (2013) and has been pruned to include
 only taxa sampled in this study.  **Purpose:** Phylogeny for the
 phylogenetic MANOVA described in the manuscript. **Associated files:** *
 `extantlizard_avgs.csv` — extant lizard morphometric dataset. *
 `code_phylogenetic_MANOVA.R` — R script implementing the phylogenetic
 MANOVA using this tree. #### File: MartinezandJenkins_SuppFigure1.tiff
 **Description:** Scatterplot of log-transformed head length (HL) versus
 snout–vent length (SVL) for extant lizard species, with fitted regression
 line, 95 % confidence intervals, and taxonomic group labels.  **Purpose:**
 To validate head length as a robust predictor of body size (SVL) and
 justify its use in cross-taxonomic comparisons involving fossil taxa. 
 **Associated datasets:** `extantlizard_avgs.csv` and
 `procolophonid_avgs.csv`. **Usage:** This figure serves as a
 methodological reference for interpreting head-length-based scaling
 analyses. It may be cited alongside the associated datasets to illustrate
 the allometric relationship between cranial and body size variables. ####
 File: Supplemental_Table_1_lizard_and_proco_SVLs_headlengthdata.csv
 **Description:** Snout–vent length (SVL) and head length (HL) data for
 both extant lizard species and fossil specimens. Each row represents a
 specimen or species mean, with accompanying identifiers and measurement
 metadata. Data were compiled to assess scaling relationships between head
 length and overall body size across living and extinct reptiles. This
 supplemental table includes the sources for SVL and HL data for each taxon
 included in the dataset.  ## Code/software `code_phylogenetic_MANOVA.R`
 This file conducts the phylogenetic multivariate analysis of variance
 described in the manuscript. This file uses ultrametric_lizardtree.newick
 as the phylogenetic tree in analysis.  *Language and Environment* R
 Environment for Statistical Computing  *Version* 4.4.3 *Dependencies* *
 geiger * ape * phytools * maps `code_LDA.R` This file performs the linear
 discriminant analyses (LDAs) described in the manuscript. This file uses
 extantlizards_avgs.csv and procolophonid_avgs.csv as the datasets for the
 LDAs.  *Language and Environment* R Environment for Statistical Computing 
 *Version* 4.4.3 *Dependencies* * ggplot2 * MASS * cowplot * dplyr