High-precision body mass predictors for small mammals: A case study in the Mesozoic

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 whe..., 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 ..., , # 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.

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