Anhanguera taxonomy revisited: is our understanding of Santana Group pterosaur diversity biased by poor biological and stratigraphic control?
Anhanguera taxonomy revisited: is our understanding of Santana Group pterosaur diversity biased by poor biological and stratigraphic control?
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作者：
Pinheiro FL;Rodrigues T
Anhanguerids是翼龙的一个重要分支，主要是从早白垩世Romualdo地层（巴西东北部）发现的数十个三维保存标本中得知的。它们在这个沉积单元中非常多样化，有8个命名的物种，其中6个属于Anhanguera属。然而，这种多样性可能被高估了，因为这些物种在历史上是根据细微的差异来诊断的，主要是基于颅嵴的形状和位置。尽管如此，最近发现的翼龙分类群代表了大量的个体，包括青少年和成年人，以及假定的男性和女性，有大小和形状的嵴，要么是个体发育可变或性别二型。我们详细描述了头骨的最完整的标本之一，称为Anhanguera，AMNH 22555，并使用它作为一个案例研究，以审查的多样性anhanguerids从Romualdo形成。为了实现这一点，进行了几何形态分析，以评估大小依赖字符相对于前上颌骨嵴在12个最完整的头骨轴承波峰，是指，或相关的，这个分支，几乎所有的人都分析了第一手资料。几何形态回归的形状对质心大小是高度统计学显着的（p = 0.0091），并表明异速生长占25.7%的总形状之间的变化不同的质心大小的头骨。在较大的头骨中，前上颌骨嵴更高，前后更长，这一特征与个体发育相一致。提出了一种新的诊断Anhanguera，包括现在已知的属内广泛分布的性状，以及个体发育变化。AMNH 22555不能被称为“Anhanguera santanae”，事实上，“Anhanguera santanae”，“Anhanguera araripensis”和“Anhanguera robustus”在这里被认为是可疑名称。在历史上，冠形态的微小差异已被用于新的anhanguerid物种的定义。如今，这种做法导致了相当大的困难，指保存完好的头骨到已知的类群。当几个标本进行分析，形态以前被认为是不同的，事实上，分开的连续，因此更好地解释为个人或时间的变化。对Romualdo组的地层控制挖掘显示了关于鱼类群落的动物区系更替的证据。因此，这个单位中的一些翼龙可能不是同时代的，甚至可能代表了再生的形态模式。不幸的是，业余爱好者收集罗穆阿尔多组化石，特别是针对商业，导致缺乏几乎所有翼龙的地层数据，并排除了这些进一步的假设测试。
Anhanguerids comprise an important clade of pterosaurs, mostly known from dozens of three-dimensionally preserved specimens recovered from the Lower Cretaceous Romualdo Formation (northeastern Brazil). They are remarkably diverse in this sedimentary unit, with eight named species, six of them belonging to the genus Anhanguera. However, such diversity is likely overestimated, as these species have been historically diagnosed based on subtle differences, mainly based on the shape and position of the cranial crest. In spite of that, recently discovered pterosaur taxa represented by large numbers of individuals, including juveniles and adults, as well as presumed males and females, have crests of sizes and shapes that are either ontogenetically variable or sexually dimorphic. We describe in detail the skull of one of the most complete specimens referred to Anhanguera, AMNH 22555, and use it as a case study to review the diversity of anhanguerids from the Romualdo Formation. In order to accomplish that, a geometric morphometric analysis was performed to assess size-dependent characters with respect to the premaxillary crest in the 12 most complete skulls bearing crests that are referred in, or related to, this clade, almost all of them analyzed first hand. Geometric morphometric regression of shape on centroid size was highly statistically significant (p = 0.0091) and showed that allometry accounts for 25.7% of total shape variation between skulls of different centroid sizes. Premaxillary crests are both taller and anteroposteriorly longer in larger skulls, a feature consistent with ontogenetic growth. A new diagnosis is proposed for Anhanguera, including traits that are nowadays known to be widespread within the genus, as well as ontogenetic changes. AMNH 22555 cannot be referred to “Anhanguera santanae” and, in fact, “Anhanguera santanae”, “Anhanguera araripensis”, and “Anhanguera robustus” are here considered nomina dubia. Historically, minor differences in crest morphology have been used in the definition of new anhanguerid species. Nowadays, this practice resulted in a considerable difficulty in referring well-preserved skulls into known taxa. When several specimens are analyzed, morphologies previously believed to be disparate are, in fact, separated by a continuum, and are thus better explained as individual or temporal variations. Stratigraphically controlled excavations on the Romualdo Formation have showed evidence for faunal turnover regarding fish communities. It is thus possible that some of the pterosaurs from this unit were not coeval, and might even represent anagenetic morphotypes. Unfortunately, amateur collecting of Romualdo Formation fossils, aimed especially at commerce, resulted in the lack of stratigraphic data of virtually all its pterosaurs and precludes testing of these further hypotheses.