The evolution of the platyrrhine talus: A comparative analysis of the phenetic affinities of the Miocene platyrrhines with their modern relatives

Abstract

Platyrrhines are a diverse group of primates that presently occupy a broad range of tropical-equatorial environments in the Americas. However, most of the fossil platyrrhine species of the early Miocene have been found at middle and high latitudes. Although the fossil record of New World monkeys has improved considerably over the past several years, it is still difficult to trace the origin of major modern clades. One of the most commonly preserved anatomical structures of early platyrrhines is the talus. This work provides an analysis of the phenetic affinities of extant platyrrhine tali and their Miocene counterparts through geometric morphometrics and a series of phylogenetic comparative analyses. Geometric morphometrics was used to quantify talar shape affinities, while locomotor mode percentages (LMPs) were used to test if talar shape is associated with locomotion. Comparative analyses were used to test if there was convergence in talar morphology, as well as different models that could explain the evolution of talar shape and size in platyrrhines. Body mass predictions for the fossil sample were also computed using the available articular surfaces. The results showed that most analyzed fossils exhibit a generalized morphology that is similar to some ‘generalist’ modern species. It was found that talar shape covaries with LMPs, thus allowing the inference of locomotion from talar morphology. The results further suggest that talar shape diversification can be explained by invoking a model of shifts in adaptive peak to three optima representing a phylogenetic hypothesis in which each platyrrhine family occupied a separate adaptive peak. The analyses indicate that platyrrhine talar centroid size diversification was characterized by an early differentiation related to a multidimensional niche model. Finally, the ancestral platyrrhine condition was reconstructed as a medium-sized, generalized, arboreal, quadruped.

Inferring locomotor behaviours in Miocene New World monkeys using finite element analysis, geometric morphometrics and machine-learning classification techniques applied to talar morphology

“… a Body mass estimates from Püschel et al [ 6 ]. b Specimens that have not been taxonomically assigned.…”

“…Extant body mass data were obtained from Smith & Jungers [ 27 ], while the fossil body mass predictions were obtained from Püschel et al [ 6 ]. Among living platyrrhine species, male and female body mass are highly correlated [ 29 ]; therefore, average body mass was used in the subsequent analyses (tables 1 and 2 ).…”

“…After teeth, the talus is probably the most commonly preserved anatomical element in the platyrrhine fossil record [ 3 ], with several Miocene taxa possessing at least one conserved talus [ 6 ]. Importantly, talar morphology can provide insights about postural adaptations due to its interconnection with other foot bones [ 7 , 8 ].…”

“…There is a strong and significant association between talar shape and locomotor behaviour [ 6 ], and evidence shows that bone is functionally adapted to the mechanical demands that are imposed during life [ 11 ]. Therefore, it is logical to hypothesize that talar mechanical strength associated with biomechanical performance could also be used to distinguish and infer locomotor behaviours.…”

Cranial and endocranial diversity in extant and fossil atelids (Platyrrhini: Atelidae): A geometric morphometric study

“…The results of this study show the importance of considering both extant and fossil species when exploring diversification in complex traits, such as endocranial and cranial shape variation. Several recent studies analyzed cranial and mandibular shape variation in extant and fossil species of primates and other mammalian clades (e.g., Álvarez, Perez, & Verzi, ; Fleagle et al, ; Gunz et al, ; Püschel, Gladman, Bobe, & Sellers, ; Rocatti et al, ), and they also show the importance of fossil variation for understanding clade evolution. In particular, the joint use of data from fossil and extant species allows us to consider variation from periods predating or concomitant with events of mass extinction.…”