Data from: Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity

With a single complete mandible and 56 mandibular symphyseal fragments of various sizes, the Late Cretaceous Hungarian azhdarchid material has been considered one of the most extensive monospecific pterosaur assemblages in the world. Representing a broad size range, these elements have been thought to demonstrate a developmental series of Bakonydraco galaczi. As such, they were ideal to test whether absolute size and/or morphology reliably indicate relative ontogenetic stages in this pterosaur. Forty-five specimens were selected for multivariate morphometrics and classified into four size classes. After acquiring the morphometric data set, we thin-sectioned eight symphyses representing all size groups and classified them into relative ontogenetic stages based on qualitative microstructural inspection prior to quantitative histological analyses. Microstructural characters suggestive of developmental state were then quantified for intra- and interindividual uni- and multivariate analyses to test the correspondence among the results of qualitative and quantitative analyses. In contrast to our expectations, histological features identified the smallest specimen as an adult and not an early juvenile. The substantial size difference between this specimen and other adults, along with its distinct microanatomical and histological features, implies the presence of at least two pterosaur taxa in this symphysis assemblage. This hypothesis is further supported by multivariate morphometrics, which separate the smallest symphyses from all other specimens that form one continuous group. Although the latter group also shows considerable size variability in corresponding ontogenetic stages, this suggests developmental plasticity rather than the presence of even more taxa, and indicates that symphysis size and morphology are poor indicators of skeletal maturity in these animals. Hence, bone histology is an important independent test of the assessment of ontogenetic stage using size and morphology.

晚白垩世匈牙利产出的阿兹达奇翼龙类（azhdarchid）标本群包含1件完整下颌骨与56件不同尺寸的下颌联合骨碎片，该标本群被认为是全球范围内保存最为丰富的单种翼龙化石组合之一。这批标本涵盖了广泛的尺寸区间，此前被认为代表了巴科尼翼龙（Bakonydraco galaczi）的个体发育序列，因此非常适合用于验证该翼龙的绝对体型与/或形态是否能够可靠反映其相对个体发育阶段。研究人员选取45件标本开展多变量形态测量学（multivariate morphometrics）分析，并将其划分为4个尺寸等级。在获取形态测量数据集后，我们对代表所有尺寸组的8件下颌联合碎片制作了薄切片，先通过定性显微结构观察将其划分为相对个体发育阶段，随后开展定量组织学分析。此后，对能够反映发育状态的显微结构特征进行量化，开展个体内、个体间的单变量与多变量分析，以验证定性与定量分析结果的一致性。与研究预期相悖的是，组织学特征显示尺寸最小的标本为成年个体，而非早期幼体。该标本与其余成年个体间存在显著体型差异，加之其独特的显微解剖学与组织学特征，表明该下颌联合组合中至少存在2个翼龙类群。这一假说得到了多变量形态测量学结果的进一步支持：最小的下颌联合碎片标本与其余标本被明显区分，其余标本则构成一个连续的类群。尽管该类群内部同样存在可观的体型差异，对应不同的个体发育阶段，但这提示该类群存在发育可塑性，而非存在更多类群；同时也表明，对于这类动物而言，下颌联合的尺寸与形态并不能可靠反映骨骼成熟度。因此，骨骼组织学是验证通过体型与形态评估个体发育阶段的重要独立方法。