Data from: Morphometric variation of extant platyrrhine molars: taxonomic implications for fossil platyrrhines

The phylogenetic position of many fossil platyrrhines with respect to extant ones is not yet clear. Two main hypotheses have been proposed: the layered or successive radiations hypothesis suggests that Patagonian fossils are Middle Miocene stem platyrrhines lacking modern descendants, whereas the long lineage hypothesis argues for an evolutionary continuity of all fossil platyrrhines with the extant ones. Our geometric morphometric analysis of a 15 landmark-based configuration of platyrrhines’ first and second lower molars suggest that morphological stasis may explain the reduced molar shape variation observed. Platyrrhine lower molar shape might be a primitive retention of the ancestral state affected by strong ecological constraints throughout the radiation of the main platyrrhine families. The Patagonian fossil specimens showed two distinct morphological patterns of lower molars, Callicebus—like and Saguinus—like, which might be the precursors of the extant forms, whereas the Middle Miocene specimens, though showing morphological resemblances with the Patagonian fossils, also displayed new, derived molar patterns, Alouatta—like and Pitheciinae—like, thereby suggesting that despite the overall morphological stasis of molars, phenotypic diversification of molar shape was already settled during the Middle Miocene.

许多化石阔鼻猴类（Platyrrhines）相对于现生类群的系统发育位置目前尚未明确。目前已提出两种主流假说：分层（或连续）辐射假说认为，巴塔哥尼亚化石类群属于中新世中期的干群阔鼻猴类，且无现生后代；而长谱系假说则主张所有化石阔鼻猴类均与现生类群存在演化连续性。
我们针对阔鼻猴类第一、第二下臼齿的15个解剖标志点构型开展几何形态测量学分析，结果显示，形态停滞或许可以解释观测到的臼齿形态变异程度降低的现象。
阔鼻猴类的下臼齿形态，或许是在主要阔鼻猴类科的辐射演化过程中，受强烈生态约束作用所保留下来的祖征状态。
巴塔哥尼亚化石标本展现出两种截然不同的下臼齿形态模式——类似伶猴属（Callicebus）的形态与类似柽柳猴属（Saguinus）的形态，这两类形态或许是现生类群的祖先类型；而中新世中期的标本尽管与巴塔哥尼亚化石类群存在形态相似性，却也呈现出两种全新的衍生臼齿形态模式：类似吼猴属（Alouatta）的形态与类似僧面猴亚科（Pitheciinae）的形态。由此表明，尽管臼齿整体呈现形态停滞特征，但臼齿形态的表型分化其实在中新世中期就已经发生。