Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2.
BMC Biol. 2012 Jul 10;10:60. doi: 10.1186/1741-7007-10-60.
Body size is intimately related to the physiology and ecology of an organism. Therefore, accurate and consistent body mass estimates are essential for inferring numerous aspects of paleobiology in extinct taxa, and investigating large-scale evolutionary and ecological patterns in the history of life. Scaling relationships between skeletal measurements and body mass in birds and mammals are commonly used to predict body mass in extinct members of these crown clades, but the applicability of these models for predicting mass in more distantly related stem taxa, such as non-avian dinosaurs and non-mammalian synapsids, has been criticized on biomechanical grounds. Here we test the major criticisms of scaling methods for estimating body mass using an extensive dataset of mammalian and non-avian reptilian species derived from individual skeletons with live weights.
Significant differences in the limb scaling of mammals and reptiles are noted in comparisons of limb proportions and limb length to body mass. Remarkably, however, the relationship between proximal (stylopodial) limb bone circumference and body mass is highly conserved in extant terrestrial mammals and reptiles, in spite of their disparate limb postures, gaits, and phylogenetic histories. As a result, we are able to conclusively reject the main criticisms of scaling methods that question the applicability of a universal scaling equation for estimating body mass in distantly related taxa.
The conserved nature of the relationship between stylopodial circumference and body mass suggests that the minimum diaphyseal circumference of the major weight-bearing bones is only weakly influenced by the varied forces exerted on the limbs (that is, compression or torsion) and most strongly related to the mass of the animal. Our results, therefore, provide a much-needed, robust, phylogenetically corrected framework for accurate and consistent estimation of body mass in extinct terrestrial quadrupeds, which is important for a wide range of paleobiological studies (including growth rates, metabolism, and energetics) and meta-analyses of body size evolution.
体型与生物体的生理学和生态学密切相关。因此，准确一致的体重估计对于推断已灭绝类群的许多古生物学方面以及研究生命历史中大规模的进化和生态模式至关重要。鸟类和哺乳动物骨骼测量值与体重之间的比例关系通常用于预测这些冠群中已灭绝成员的体重，但这些模型对于预测更为遥远的谱系分类群（如非鸟类恐龙和非哺乳动物合弓类动物）的体重的适用性，从生物力学角度受到了批评。在这里，我们使用来自具有活体重量的单个骨骼的哺乳动物和非鸟类爬行动物物种的大量数据集来测试用于估计体重的比例关系方法的主要批评。
在比较肢体比例和肢体长度与体重时，注意到哺乳动物和爬行动物的肢体比例存在显著差异。然而，令人惊讶的是，尽管现存的陆地哺乳动物和爬行动物的肢体姿势、步态和系统发育历史不同，但近端（肢带）肢体骨骼周长与体重之间的关系高度保守。因此，我们能够明确拒绝质疑普遍比例关系方程适用于估计远缘分类群体重的主要批评。
肢带周长与体重之间关系的保守性表明，主要承重骨骼的最小骨干周长受作用于肢体的各种力（即压缩或扭转）的影响较弱，而与动物的质量关系最强。因此，我们的结果为准确一致地估计已灭绝的陆地四足动物的体重提供了急需的、稳健的、系统发育校正框架，这对于广泛的古生物学研究（包括生长速度、新陈代谢和能量学）和对身体大小进化的荟萃分析都很重要。
