Data from: Paleohistological estimation of bone growth rate in extinct archosaurs

The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.

主龙类（Archosauria）演化支包含两个在物种多样性与形态分异度上差异悬殊的姊妹群：鳄形类（Crurotarsi，即与鳄鱼亲缘关系近于鸟类的类群）与鸟颈类主龙类（Ornithodira，涵盖翼龙与包含鸟类在内的恐龙类群）。就生长模式与代谢速率而言，现生鳄形类类群或是过往生物多样性研究中存在采样偏倚的样本。骨组织学特征可在化石记录中留存数亿年，其潜在蕴含已灭绝脊椎动物的个体死亡年龄、性成熟年龄、骨生长速率以及基础代谢率相关信息。
我们以现生羊膜动物为样本，构建了一款可通过骨组织学特征估算骨生长速率的古生物学模型。交叉验证测试结果证实该模型具备可靠性。随后我们将其应用于包含鳄形类与鸟颈类主龙类在内的已灭绝主龙类样本的骨生长速率估算。
在完成系统发育信号检测后，通过平方变化简约法将股骨生长速率优化映射至羊膜动物时间校准系统发育树的分析结果显示，存在两种截然不同的演化趋势：从鸟颈类主龙类的最近共同祖先至现生鸟类，骨生长速率呈上升态势；而从鳄形类的最近共同祖先至现生鳄鱼，骨生长速率则呈下降趋势。
不过，基于近期关于鳄鱼肺部存在单向气流的研究证据，我们认为鳄鱼或仍保留了高速生长的能力。