DOI: 10.5061/dryad.tmpg4f550
title: High-precision body mass predictors for small mammals: A case study in the Mesozoic

description: Body mass is a pivotal quantity in palaeobiology but must be estimated
 from an imperfect fossil record. We analyse the precision of skeletal
 predictors of mammalian body mass as a mean to inform the Mesozoic mammal
 record, including a new eutriconodont from North America. We focus on the
 critical small end of the size spectrum – critical because the earliest
 mammals were small, because small size persisted onto the stems of the
 major extant radiations, and because small mammals compose a large
 proportion of crown diversity. Linear regressions based on extant small
 mammals indicate a universal correlation of body mass with observed
 measurements, but with clear differences in precision. Postcranial
 predictors outperform jaw and dental metrics, with certain femoral joint
 dimensions providing surprisingly precise estimations. Overall, our data
 indicate small-mammal evolution during the Mesozoic unfolded in patterns
 of underappreciated complexity. Studying these dynamics is only possible
 when estimating body mass within a strict, highly focused phylogenetic
 context. The heuristic value of the estimators we provide here are not
 limited to the Mesozoic but are phylogenetically justified for any
 small-bodied mammal regardless of age.
description: For extant samples,
 craniodental measurements were taken using Paleo-Tech Dental Caliper with
 a Mitutoyo 0-150 mm digital scale to the nearest 0.01mm. Limb measurements
 and measurements of the specimens from KUNHM were taken with a SPI Dial
 Caliper Model 31-415-3 to the nearest 0.05 mm. If specimens
 had both left and right sides, we used measurements from the more complete
 side and supplemented from the contralateral side if
 necessary. For fossil
 specimens, we recorded measurements from literature. For specimens lacking
 published measurements of preserved predictors, we used published figures
 and ImageJ to add measurements where possible. This approach included
 calibrating the line tool with the published scale bar and then using this
 tool for measurement. Where possible, we also compared our figure-based
 measurements with published values to ensure accuracy. Because we could
 not verify the angle of the limb elements in specimens preserved in slabs,
 we measured the midshaft diameter of the femur and humerus and included
 these measures as both anteroposterior and mediolateral diameters for
 analysis. We acquired measurements of Gobiconodon ostromi from quality
 casts of MCZ 19965 and MCZ 19860 housed the Center for Functional Anatomy
 and Evolution at Johns Hopkins University. From these specimens, we added
 or amended a limited number of postcranial
 measurements.
description: # Data from: High-precision body mass predictors for small mammals: a case
 study in the Mesozoic One
 collection of extant therian dentoskeletal measurments, one collection of
 Eutriconodonta dentoskeletal measurments, and one collection of
 Eutriconodonta body mass predictions. ## Description of the data and file
 structure 'data.csv' is the csv file containing measurements of
 extant therians, 'eutridata.csv' is the csv file containing
 measurements of Eutriconodonta and 'allmass.csv' is the file for
 plotting the figure of fossil mass prediction. 'pgls.tre' and
 'pglstime.tre' are tree files in Newick format required to run
 the below R markdown file. For data.csv, NA represents missing values due
 to either the absence or immeasurability of the structure. For
 eutridata.csv, the associated specimen for a measurement is either next to
 the measurement in the 'name' column, or the first one above in
 that column; the same is true for the associated publication in the
 'Publication' column. For allmass.csv, the different number of
 rows for the columns is due to differences in number of predictors
 avaiable for each species. ## Code/Software The R markdown file was last
 run with RStudio version 2023.06.1+524 and R version 4.3.1. Required
 packages include gt, gridExtra, tidyverse, glue, data.table, kableExtra,
 knitr, ape, maps, phytools, geiger, nlme, caret, schoolmath.