Dental measurements do not diagnose modern artiodactyl species: Implications for the systematics of Merycoidodontoidea

Abstract

Though dental measurements are frequently used to diagnose the fossil species of Merycoidodontoidea and other extinct artiodactyls, the effective diagnosis of modern artiodactyl taxa via dental measurements has not been extensively tested. Our study finds that variation in artiodactyl dentition is generally higher than in primates, carnivores, rodents and even elephants, with molar coefficients of variation ranging up to 18% (Camelus bactrianus), and that dental measurements poorly diagnose modern artiodactyls via discriminant function analysis, adjusted t-tests on coefficients of variation, or finite mixture analysis. The higher-than-expected coefficients of variation for artiodactyls imply that some fossil taxa may be over-split, but the low utility of dental measurements in separating sympatric species of duikers also suggests that dental measurements are not effective for fully diagnosing certain artiodactyl groups. We advocate a systematic revision of Merycoidodontoidea and many other fossil artiodactyl groups with lower emphasis on dental measurements and better accounting for the ways selenodont dentition varies.

A new early occurrence of Cervidae in North America from the Miocene-Pliocene Ellensburg Formation in Washington, USA

“…The p2 of UWBM VP 117138 is within two standard deviations of the lengths and widths of Bretzia, Capreolus, and Odocoileus hemionus, but exceeds two standard deviations of the average width of Eocoileus and is nearly half the length of Odocoileus lucasi (Table 1). The CV of p2 widths of Eocoileus reported by Vislobokova (1995) was 9.6 %, which is similar to the measured variation in Odocoileus in this study and is closer to what is expected for a mid-sized artiodactyl (Emery-Wetherell and Davis, 2018), and therefore the difference in size between our specimen and Eocoileus is likely biologically meaningful. Odocoileus lucasi is considerably larger, with a p2 length approximately twice as long as any of the other species we considered -on par with the size of Cervus elaphus.…”

“…In all other measurements UWBM VP 117138 is indistinguishable from nearly all considered species, except Odocoileus lucasi. Though the lengths of m2 and m3 are smaller than two standard deviations of Bretzia, the population of Bretzia measured by Gustafson (2015) is far less variable than is typical in mid-sized artiodactyls (Emery-Wetherell and Davis, 2018). The maximum lengths of artiodactyl teeth are often smaller in older adults with worn teeth (Emery-Wetherell and Davis, 2018), and given that UWBM VP 117138 is very worn, it is possible it is simply older and therefore smaller than the measured specimens of Bretzia reported by Gustafson (2015), or that the size difference may arise only from being found at different localities.…”

“…Molar widths of UWBM VP 117138 are within two standard deviations of the measurements taken on the molars of Bretzia, but are smaller than two standard deviations of the lengths reported by Gustafson (2015). Artiodactyl teeth do decrease in length as they are worn (Emery-Wetherell and Davis, 2018), and the significantly worn molars of UWBM VP 117138 may be the cause of their smaller size. It is also worth noting that the Coefficients of Variation (CV) provided by Gustafson (2015) for m2 and m3 lengths of Bretzia (m2: CV = 6.06 %; m3: CV = 4.67 %) are smaller than those we measured for Odocoileus (m2: CV = 7.81 %; m3: CV = 18.27 %), and are much smaller than is typical for artiodactyl teeth (Emery-Wetherell and Davis, 2018).…”

“…Artiodactyl teeth do decrease in length as they are worn (Emery-Wetherell and Davis, 2018), and the significantly worn molars of UWBM VP 117138 may be the cause of their smaller size. It is also worth noting that the Coefficients of Variation (CV) provided by Gustafson (2015) for m2 and m3 lengths of Bretzia (m2: CV = 6.06 %; m3: CV = 4.67 %) are smaller than those we measured for Odocoileus (m2: CV = 7.81 %; m3: CV = 18.27 %), and are much smaller than is typical for artiodactyl teeth (Emery-Wetherell and Davis, 2018). Given that, it is possible that the averages and standard deviation reported by Gustafson (2015) are conservative, and that measurements taken on UWBM VP 117138 are within two standard deviations of all dental measurements of both species.…”

Species Diversity in the Hypertragulid (Mammalia: Artiodactyla) Population of the John Day Basin, Oregon

“…For groups with a sample size smaller than n = 5, I used a small-sample correction (Sokal & Braumann, 1980) shown in Equation 2 . = * 100 (1) = * (1 + 1 4 * ) * 100 (2) I compared measurements of upper molars of the fossil hypertragulids to the modern southern red muntjac, Muntiacus muntjak, using data from Emery-Wetherell & Davis (2018). I compared the lower molars to modern M. muntjak, Muntjack.…”