Dietary habits in extinct species cannot be directly observed; thus, in the absence of extraordinary evidence, they must be reconstructed with a combination of morphological proxies. Such proxies often include information on dental organization and function such as tooth formation time and tooth replacement rate. In extinct organisms, tooth formation times and tooth replacement rate are calculated, in part via extrapolation of the space between incremental lines in dental tissues representing daily growth (von Ebner Line Increment Width; VEIW). However, to date, little work has been conducted testing assumptions about the primary data underpinning these calculations, specifically, the potential impact of differential sampling and data extrapolation protocols. To address this, we tested a variety of intradental, intramandibular, and ontogentic sampling effects on calculations of mean VEIW, tooth formation times, and replacement rates using histological sections and CT reconstructions of a growth series of three specimens of the extant archosaurian Alligator mississippiensis. We find transect position within the tooth and transect orientation with respect to von Ebner lines to have the greatest impact on calculations of mean VEIW—a maximum number of VEIW measurements should be made as near to the central axis (CA) as possible. Measuring in regions away from the central axis can reduce mean VEIW by up to 36%, causing inflated calculations of tooth formation time. We find little demonstrable impact to calculations of mean VEIW from the practice of subsampling along a transect, or from using mean VEIW derived from one portion of the dentition to extrapolate for other regions of the dentition. Subsampling along transects contributes only minor variations in mean VEIW (<12%) that are dwarfed by the standard deviation (SD). Moreover, variation in VEIW with distance from the pulp cavity likely reflects idiosyncratic patterns related to life history, which are difficult to control for; however, we recommend increasing the number of VEIW measured to minimize this effect. Our data reveal only a weak correlation between mean VEIW and body length, suggesting minimal ontogenetic impacts. Finally, we provide a relative SD of mean VEIW for Alligator of 29.94%, which can be used by researchers to create data-driven error bars for tooth formation times and replacement rates in fossil taxa with small sample sizes. We caution that small differences in mean VEIW calculations resulting from non-standardized sampling protocols, especially in a comparative context, will produce inflated error in tooth formation time estimations that intensify with crown height. The same holds true for applications of our relative SD to calculations of tooth formation time in extinct taxa, which produce highly variable maximum and minimum estimates in large-toothed taxa (e.g., 718–1,331 days in Tyrannosaurus).

中文翻译：

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采样影响主龙牙齿生长和更换率的评估：对古生物学研究的影响

无法直接观察已灭绝物种的饮食习惯；因此，在没有特别证据的情况下，它们必须用形态学代理的组合来重建。此类代理通常包括有关牙齿组织和功能的信息，例如牙齿形成时间和牙齿更换率。在已灭绝的生物体中，计算牙齿形成时间和牙齿更换率，部分通过外推牙齿组织中代表每日生长的增量线之间的空间（von Ebner Line Increment Width; VEIW）。然而，迄今为止，几乎没有对支持这些计算的主要数据的假设进行测试，特别是差异采样和数据外推协议的潜在影响。为了解决这个问题，我们测试了各种牙内、下颌内、使用组织学切片和 CT 重建现存的主龙类鳄鱼密西西比鳄鱼的三个标本的生长系列，计算平均 VEIW、牙齿形成时间和更换率的个体发生采样效应。我们发现牙齿内的横断面位置和相对于 von Ebner 线的横断面方向对平均 VEIW 的计算影响最大——应尽可能靠近中心轴 (CA) 进行最大数量的 VEIW 测量。在远离中心轴的区域进行测量可以将平均 VEIW 降低多达 36%，从而导致牙齿形成时间的计算膨胀。我们发现沿样带进行二次抽样的做法对平均 VEIW 的计算几乎没有明显影响，或使用从牙列的一部分导出的平均 VEIW 来推断牙列的其他区域。沿横断面的子采样仅导致平均 VEIW (<12%) 的微小变化，这与标准偏差 (SD) 相形见绌。此外，VEIW 与牙髓腔距离的变化可能反映了与生活史相关的特殊模式，这些模式难以控制；但是，我们建议增加测量的 VEIW 数量以尽量减少这种影响。我们的数据仅显示平均 VEIW 与体长之间的弱相关性，表明对个体发育的影响最小。最后，我们提供了 29.94% 的鳄鱼平均 VEIW 的相对 SD，研究人员可以使用它来为小样本量的化石分类群中的牙齿形成时间和替换率创建数据驱动的误差条。我们警告说，由非标准化采样协议导致的平均 VEIW 计算的微小差异，特别是在比较背景下，会在牙齿形成时间估计中产生夸大的误差，并随着牙冠高度而加剧。将我们的相对标准差应用于已灭绝分类群中牙齿形成时间的计算也是如此，这会在大齿类群中产生高度可变的最大值和最小值估计值（例如，霸王龙的 718-1,331 天）。