Data from: Do different disparity proxies converge on a common signal? Insights from the cranial morphometrics and evolutionary history of Pterosauria (Diapsida: Archosauria)

Disparity, or morphological diversity, is often quantified by evolutionary biologists investigating the macroevolutionary history of clades over geological timescales. Disparity is typically quantified using proxies for morphology, such as measurements, discrete anatomical characters, or geometric morphometrics. If different proxies produce differing results, then the accurate quantification of disparity in deep time may be problematic. However, despite this, few studies have attempted to examine disparity of a single clade using multiple morphological proxies. Here, as a case study for this question, we examine the disparity of the volant Mesozoic fossil reptile clade Pterosauria, an intensively studied group that achieved substantial morphological, ecological, and taxonomic diversity during their 145+ million year evolutionary history. We characterise broadscale patterns of cranial morphological disparity for pterosaurs for the first time using landmark-based geometric morphometrics, and make comparisons to calculations of pterosaur disparity based on alternative metrics. Landmark-based disparity calculations suggest that monofenestratan pterosaurs were more diverse cranially than basal non-monofenestratan pterosaurs (at least when the aberrant anurognathids are excluded), and that peak cranial disparity may have occurred in the Early Cretaceous, relatively late in pterosaur evolution. Significantly, our cranial disparity results are broadly congruent with those based on whole skeleton discrete character and limb proportion datasets, indicating that these divergent approaches document a consistent pattern of pterosaur morphological evolution. Therefore, pterosaurs provide an exemplar case demonstrating that different proxies for morphological form can converge on the same disparity signal, which is encouraging because often only one such proxy is available for extinct clades represented by fossils. Furthermore, mapping phylogeny into cranial morphospace demonstrates that pterosaur cranial morphology is significantly correlated with, and potentially constrained by, phylogenetic relationships.

形态差异度（disparity），或称形态多样性（morphological diversity），常被进化生物学家用于量化地质时间尺度下演化支（clade）的宏观进化历史。形态差异度通常通过形态替代指标进行量化，例如测量数据、离散解剖学特征或几何形态测量学（geometric morphometrics）。若不同替代指标所得结果存在差异，则深时尺度下形态差异度的精准量化可能存在难题。尽管如此，鲜有研究尝试采用多种形态替代指标对单一演化支的形态差异度展开分析。作为该问题的案例研究，我们针对中生代会飞的化石爬行类演化支翼龙目（Pterosauria）的形态差异度展开分析——这一类群被广泛研究，在其长达1.45亿余年的演化历程中形成了丰富的形态、生态与分类多样性。我们首次采用基于地标点的几何形态测量学，刻画翼龙颅部形态差异度的宏观格局，并与基于其他替代度量指标的翼龙形态差异度计算结果进行对比。基于地标点的差异度计算结果显示，单窗孔翼龙类的颅部多样性高于基底非单窗孔翼龙类（至少在排除异常的无尾翼龙科（anurognathids）的情况下），且颅部形态差异度的峰值可能出现在翼龙演化历程相对较晚的早白垩世。值得注意的是，我们的颅部形态差异度分析结果与基于全骨架离散特征数据集及肢体比例数据集的分析结果大体一致，表明这些不同的研究方法能够揭示翼龙形态进化的一致模式。因此，翼龙可为一项范例案例：不同的形态替代指标可收敛得到相同的差异度信号，这一点令人备受鼓舞，因为对于以化石为代表的已灭绝演化支而言，往往仅能获取一种此类替代指标。此外，将系统发育关系映射至颅部形态空间的分析表明，翼龙的颅部形态与系统发育关系显著相关，且可能受系统发育关系所约束。