Abstract
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.
Highlights
The ‘‘long lineages’’ hypothesis argues that the oldest known Patagonian fossils (16– 20 Ma) are to be included within the extant Platyrrhines (Rosenberger, 1979; Rosenberger, 1980; Rosenberger, 1981; Rosenberger, 1984; Rosenberger et al, 2009; Tejedor, 2013), whereas the ‘‘layered or successive radiations’’ hypothesis suggests that these fossils constitute a geographically isolated stem group, phylogenetically unrelated to the crown platyrrhines, How to cite this article Nova Delgado et al (2016), Morphometric variation of extant platyrrhine molars: taxonomic implications for fossil platyrrhines
The aim of the present study is to use two-dimensional (2D) geometric morphometrics (GM) to quantify and analyze occulsal shape variation of lower molars (M1 and M2) of extant Platyrrhini primates to asesses the affinities of the Patagonian, Colombian, and Antillanean fossil taxa with the extant forms and to estimating the efficiency of molar shape for discriminating fossil specimens
This study develops a dental model based on molar shapes of M1 and M2 to explore phenotypic variation in extinct and extanct platyrrhines
Summary
Tejedor (2013) has suggested that Chilecebus (20 Ma), a fossil specimen (Tejedor, 2003) from the western Andean cordillera, south of Santiago de Chile, indicates that the Andean mountains did not constitute a biogeographic barrier. Hodgson et al (2009) have dated their origin between 16.8 and 23.4 Ma, suggesting an unlikely relationship of the early Miocene fossils with the crown platyrrhine clade (but see different temporal models in Goodman et al, 1998; Opazo et al, 2006; Chatterjee et al, 2009; Perelman et al, 2011; Wilkinson et al, 2011; Jameson Kiesling et al, 2014)
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