Abstract
The estimation of phylogenetic relationships and divergence times among a group of organisms is a fundamental first step toward understanding its biological diversification. The time of the most recent or last common ancestor (LCA) of extant platyrrhines is one of the most controversial among scholars of primate evolution. Here we use two molecular based approaches to date the initial divergence of the platyrrhine clade, Bayesian estimations under a relaxed-clock model and substitution rate plus generation time and body size, employing the fossil record and genome datasets. We also explore the robustness of our estimations with respect to changes in topology, fossil constraints and substitution rate, and discuss the implications of our findings for understanding the platyrrhine radiation. Our results suggest that fossil constraints, topology and substitution rate have an important influence on our divergence time estimates. Bayesian estimates using conservative but realistic fossil constraints suggest that the LCA of extant platyrrhines existed at ca. 29 Ma, with the 95% confidence limit for the node ranging from 27–31 Ma. The LCA of extant platyrrhine monkeys based on substitution rate corrected by generation time and body size was established between 21–29 Ma. The estimates based on the two approaches used in this study recalibrate the ages of the major platyrrhine clades and corroborate the hypothesis that they constitute very old lineages. These results can help reconcile several controversial points concerning the affinities of key early Miocene fossils that have arisen among paleontologists and molecular systematists. However, they cannot resolve the controversy of whether these fossil species truly belong to the extant lineages or to a stem platyrrhine clade. That question can only be resolved by morphology. Finally, we show that the use of different approaches and well supported fossil information gives a more robust divergence time estimate of a clade.
Highlights
The estimation of phylogenetic relationships and divergence times among a group of organisms is a fundamental first step toward understanding its biological diversification [1,2]
Our chronophylogenetic trees based on these mtDNA and nuclear data with their maximum likelihood values are in agreement with other recent molecular trees (Figure 3), which support the division of platyrrhines into three monophyletic families (Atelidae, Cebidae, and Pitheciidae) and suggest a sister-group phylogenetic relationship between Atelidae and Cebidae [11,13,26,69]
Previous studies suggest that this is not problematic for divergence time estimation, our results suggest that the topology has great importance for inferring the divergence time of the main platyrrhine lineages (Table 7)
Summary
The estimation of phylogenetic relationships and divergence times among a group of organisms is a fundamental first step toward understanding its biological diversification [1,2]. Hodgson et al [15] used mtDNA data and fossil calibrations to support the idea that platyrrhine diversification is characterized by two successive, sister-group radiations [16], the most recent of which is crown Platyrrhini, and to contradict the so called long lineages hypothesis of Rosenberger and co-workers [17,18,19,20], which interprets possibly all platyrrhines, living and extinct, as belonging to a single holophyletic group, and stresses the role of morphological stasis as a deep evolutionary phenomenon The latter hypothesis considers the oldest records of platyrrhines (certainly those from the early to middle Miocene of Patagonia and Chile and possibly those from the late Oligocene of Bolivia) as part of the crown Platyrrhini, phylogenetically related to the lineages of anatomically modern forms. These include the most diverse collection of platyrrhine fossils from La Venta, Colombia, deposits of middle Miocene age
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