Abstract The taxonomy of the South American river dolphins of the genus Inia has been a focus of intense debate. While traditionally it is thought to be composed of a single species with three geographically structured subspecies (Inia geoffrensis geoffrensis, I. g. humboldtiana, and I. g. boliviensis), recent molecular studies have highlighted substantial differentiation, suggesting the existence of two species (I. geoffrensis and I. araguaiaensis). Despite this evidence, the recognition of the specific status of these taxa has been hindered by inconsistent morphological diagnoses. Here, we aim to provide evidence for the morphological differentiation (or lack thereof) between subspecies and putative species. We employ geometrics and traditional morphometrics to measure skull variation to support efforts of integrative taxonomy. Our results show that morphometric diversity within the group is inconsistent with a single taxon. Morphometric evidence supports the traditional differentiation of three distinct morphotypes within the analyzed sample. These morphotypes largely correspond to described subspecies I. g. geoffrensis, I. g. humboldtiana—the latter differing from the former by size—and I. g. boliviensis, which differs from the remaining groups by shape. Furthermore, morphometric data show no differences between I. g. geoffrensis and a newly proposed species, I. araguaiaensis. Given the conservation importance of this genus and the different threats they are subject to, we strongly suggest an urgent integrative taxonomic treatment of the group to better protect these singular cetaceans.

中文翻译：

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Inia 属（鲸目，Iniidae）亚马逊河海豚头骨的形态差异与单个分类单元不一致

摘要 Inia 属南美河豚的分类一直是激烈争论的焦点。虽然传统上它被认为是由具有三个地理结构亚种（Inia geoffrensis geoffrensis、I. g. humboldtiana 和 I. g. boliviensis）的单一物种组成，但最近的分子研究强调了实质性的分化，表明存在两个物种（I. geoffrensis 和 I. araguaiaensis）。尽管有这些证据，但对这些分类群的特定状态的认识受到了不一致的形态学诊断的阻碍。在这里，我们旨在为亚种和假定物种之间的形态分化（或缺乏）提供证据。我们采用几何学和传统形态计量学来测量头骨变异，以支持综合分类学的努力。我们的结果表明，该组内的形态多样性与单个分类单元不一致。形态学证据支持分析样本中三种不同形态类型的传统区分。这些形态类型在很大程度上对应于所描述的亚种 I. g. geoffrensis, I. g. humboldtiana——后者在大小上与前者不同——而 I. g. boliviensis，其形状与其余组不同。此外，形态测量数据显示 I. g. 之间没有差异。geoffrensis 和一个新提出的物种，I. araguaiaensis。鉴于该属的保护重要性以及它们受到的不同威胁，我们强烈建议对该组进行紧急的综合分类学处理，以更好地保护这些奇异的鲸目动物。