**FIGURE 1.** Measurements taken of the m1 used in this study. m1L (total molar length, taken from anterior to posterior cingulum), m1H (molar height, from the enamel/dentine junction to tip of the protoconid), m1CA (cusp angle, from anterior cingulum to tip of protoconid to the labial cingulum posterior to the protoconid).

**FIGURE 2.** *Tapirus polkensis* dentary specimens from the Gray Fossil Site, representing examples of individuals within eruption series 2 through eruption series 7 in lateral view. ETMNH 605, 1. ETMNH 3694, 2. ETMNH 7899, 3. ETMNH 20488, 4. ETMNH 10383, 5. ETMNH 3519, 6. Scale bar equals 1 cm.

**FIGURE 3. ***Tapirus polkensis* dentary specimens from the Gray Fossil Site, representing examples of individuals within eruption series 2 through eruption series 7 in occlusal view. ETMNH 605, 1. ETMNH 3694, 2. ETMNH 7899, 3. ETMNH 20488, 4. ETMNH 10383, 5. ETMNH 3519, 6. Scale bar equals 1 cm.

**FIGURE 4.** Box plot of cusp angles (in degrees) of the m1 protoconid for each eruption series of *Tapirus polkensis* from the Gray Fossil Site. Bars represent mean values, boxes represent interquartile ranges, and whiskers represent maximum and minimum values.

**FIGURE 5.** Boxplot of crown heights of the m1 protoconid for each eruption series of *Tapirus polkensis* from the Gray Fossil Site. Bars represent mean values, boxes represent interquartile ranges, and whiskers represent maximum and minimum values.

**FIGURE 6.** Scatter plot of m1 protoconid cusp angle versus crown height for specimens in each eruption series (ES) of *Tapirus polkensis* from the Gray Fossil Site. The line represents a least squares linear regression of these data, regression equation: m1CA = 20.5 – 13.13(m1H), correlation coefficient, r = 0.932.

**FIGURE 7.** Pie chart representing the sampled population structure of *Tapirus polkensis* at the Gray Fossil Site, indicated by percentage of specimens in each eruption series (ES).