Quantification of the position and depth of the<i>flexor hallucis longus</i>groove in euarchontans, with implications for the evolution of primate positional behavior

Daubechies

et al. 2017

The Anatomical Record

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Automated geometric morphometric methods are promising tools for shape analysis in comparative biology, improving researchers' abilities to quantify variation extensively (by permitting more specimens to be analyzed) and intensively (by characterizing shapes with greater fidelity). Although use of these methods has increased, published automated methods have some notable limitations: pairwise correspondences are frequently inaccurate and pairwise mappings are not globally consistent (i.e., they lack transitivity across the full sample). Here, we reassess the accuracy of published automated methods-cPDist (Boyer et al. Proc Nat Acad Sci 108 () 18221-18226) and auto3Dgm (Boyer et al.: Anat Rec 298 () 249-276)-and evaluate several modifications to these methods. We show that a substantial percentage of alignments and pairwise maps between specimens of dissimilar geometries were inaccurate in the study of Boyer et al. (Proc Nat Acad Sci 108 () 18221-18226), despite a taxonomically partitioned variance structure of continuous Procrustes distances. We show these inaccuracies are remedied using a globally informed methodology within a collection of shapes, rather than relying on pairwise comparisons (c.f. Boyer et al.: Anat Rec 298 () 249-276). Unfortunately, while global information generally enhances maps between dissimilar objects, it can degrade the quality of correspondences between similar objects due to the accumulation of numerical error. We explore a number of approaches to mitigate this degradation, quantify their performance, and compare the generated pairwise maps (and the shape space characterized by these maps) to a "ground truth" obtained from landmarks manually collected by geometric morphometricians. Novel methods both improve the quality of the pairwise correspondences relative to cPDist and achieve a taxonomic distinctiveness comparable to auto3Dgm. Anat Rec, 301:636-658, 2018. © 2017 Wiley Periodicals, Inc.

Section: Discussionsupporting

confidence: 86%

Development and Assessment of Fully Automated and Globally Transitive Geometric Morphometric Methods, With Application to a Biological Comparative Dataset With High Interspecific Variation

Gao

Daubechies

et al. 2017

The Anatomical Record

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“…It is consistent with the perspective that Eosimiidae may be positioned more basally than stem Anthropoidea (contra [57–59]), and questions purported similarities between Eosimiidae and Tarsiidae. Furthermore, the recovered dental affinities are consistent with recent results from analyses of Eosimiidae ankle bones [31,67,68] that suggest eosimiid ankle morphology is similar to that inferred for the common ancestor of primates of modern aspect. In our opinion, these findings point to the need for continued examination of eosimiid relationships, anthropoid relationships, and certain patterns of early primate evolution.…”

Section: Discussionsupporting

confidence: 86%

Development and assessment of fully automated and globally transitive geometric morphometric methods, with application to a biological comparative dataset with high interspecific variation

Gao

Daubechies

et al. 2016

Preprint

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Automated geometric morphometric methods are promising tools for shape analysis in comparative biology: they improve researchers’ abilities to quantify biological variation extensively (by permitting more specimens to be analyzed) and intensively (by characterizing shapes with greater fidelity). Although use of these methods has increased, automated methods have some notable limitations: pairwise correspondences are frequently inaccurate or lack transitivity (i.e., they are not defined with reference to the full sample). In this study, we reassess the accuracy of two previously published automated methods, cPDist [1] and auto3Dgm [2], and evaluate several modifications to these methods. We show that a substantial fraction of alignments and pairwise maps between specimens of highly dissimilar geometries were inaccurate in the study of Boyer et al. [1], despite a taxonomically sensitive variance structure of continuous Procrustes distances. We also show these inaccuracies can be remedied by utilizing a globally informed methodology within a collection of shapes, instead of only comparing shapes in a pairwise manner (c.f. [2]). Unfortunately, while global information generally enhances maps between dissimilar objects, it can degrade the quality of correspondences between similar objects due to the accumulation of numerical error. We explore a number of approaches to mitigate this degradation, quantify the performance of these approaches, and compare the generated pairwise maps (as well as the shape space characterized by these maps) to a “ground truth” obtained from landmarks manually collected by geometric morphometricians. Novel methods both improve the quality of the pairwise correspondences relative to cPDist, and achieve a taxonomic distinctiveness comparable to auto3Dgm.

“…Overall, our results align well with scenarios of crown primate origins that emphasize vertical supports 14,50 or lemuriform-like positional behaviors 51 that rely on strong hallucal grasps. Vertical support use in the ancestral crown primate is supported by other quantitative analyses of euarchontan tali 48,52,53 and potentially the extremely elongated manual digits of early crown primates 54 . The prevalence of vertical postures among other euarchontans 19–21 strongly suggests these postures were an inherited component of the ancestral crown primate’s positional behavior.…”

Section: Discussionmentioning

confidence: 74%

“…Dynamic modeling could potentially change expression of the cam mechanism. Additionally, dorsiflexion of the primate foot involves a degree of medial rotation of the talus 8,9 , so that a lateral position for the flexor fibularis groove 47,48 or “twisting” of the PTS 35 could enhance the cam effect. These additional factors could be incorporated into future studies.…”

Section: Discussionmentioning

confidence: 99%

Vertical support use and primate origins

Feng

Dunn

et al. 2019

Sci Rep

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Adaptive scenarios of crown primate origins remain contentious due to uncertain order of acquisition and functional significance of the clade’s diagnostic traits. A feature of the talus bone in the ankle, known as the posterior trochlear shelf (PTS), is well-regarded as a derived crown primate trait, but its adaptive significance has been obscured by poorly understood function. Here we propose a novel biomechanical function for the PTS and model the talus as a cam mechanism. By surveying a large sample of primates and their closest relatives, we demonstrate that the PTS is most strongly developed in extant taxa that habitually grasp vertical supports with strongly dorsiflexed feet. Tali of the earliest fossils likely to represent crown primates exhibit more strongly developed PTS cam mechanisms than extant primates. As a cam, the PTS may increase grasping efficiency in dorsiflexed foot postures by increasing the path length of the flexor fibularis tendon, and thus improve the muscle’s ability to maintain flexed digits without increasing energetic demands. Comparisons are made to other passive digital flexion mechanisms suggested to exist in other vertebrates. These results provide robust anatomical evidence that the habitual vertical support use exerted a strong selective pressure during crown primate origins.