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（morphological disparity，亦称形态多样性）是进化生物学家在研究地质时间尺度下各演化支的宏观演化历史时，常进行量化的指标。形态差异度的量化通常采用形态学替代指标，例如形态测量数据、离散解剖学性状或几何形态测量法（geometric morphometrics）。若不同替代指标得到的结果存在分歧，则地质深时（deep time）中形态差异度的精准量化可能存在难度。尽管如此，目前鲜有研究尝试采用多种形态学替代指标，对单一演化支的形态差异度展开分析。为此，本研究以此问题为切入点，以中生代飞行爬行动物演化支翼龙目（Pterosauria）为案例展开分析。翼龙类是一类被广泛深入研究的类群，在其长达1.45亿年以上的演化历程中，演化出了丰富的形态、生态与分类学多样性。本研究首次采用基于地标点的几何形态测量法，刻画翼龙类的颅骨形态差异度宏观格局，并与基于其他度量方式的翼龙形态差异度计算结果进行对比。基于地标点的形态差异度计算结果显示，单窗孔类翼龙（Monofenestrata）的颅骨多样性高于基干非单窗孔类翼龙（至少在排除形态怪异的无尾翼龙科（Anurognathidae）类群后），且颅骨形态差异度的峰值可能出现在白垩纪早期——这一时期相对翼龙的整体演化历程而言偏晚。值得注意的是，本研究得到的颅骨形态差异度结果，与基于全身骨骼离散性状及肢体比例数据集得到的结果大体一致，这表明这些不同的分析方法均揭示了翼龙形态演化的一致模式。因此，翼龙类可为该问题提供一个典范案例：用于量化形态的不同替代指标可得到一致的形态差异度信号，这一结论令人备受鼓舞——因为在以化石为研究对象的灭绝演化支中，通常仅能获取一种此类替代指标。此外，将系统发育关系投射至颅骨形态空间的分析结果表明，翼龙的颅骨形态与系统发育关系显著相关，且可能受到系统发育关系的约束。