A critical survey of vestigial structures in the postcranial skeletons of extant mammals.

Phil Senter,John G Moch

doi:10.7717/peerj.1439

Abstract

In the Mammalia, vestigial skeletal structures abound but have not previously been the focus of study, with a few exceptions (e.g., whale pelves). Here we use a phylogenetic bracketing approach to identify vestigial structures in mammalian postcranial skeletons and present a descriptive survey of such structures in the Mammalia. We also correct previous misidentifications, including the previous misidentification of vestigial caviid metatarsals as sesamoids. We also examine the phylogenetic distribution of vestigiality and loss. This distribution indicates multiple vestigialization and loss events in mammalian skeletal structures, especially in the hand and foot, and reveals no correlation in such events between mammalian fore and hind limbs.

Highlights

A vestigial structure is a biological structure that has lost a major ancestral function and is usually drastically reduced in size
Specimen examination We examined 578 mammalian skeletal specimens and skins from 293 species (Table 1) representing 98 (70%) of the 139 extant mammal families listed by Nowak (1999)
The first criterion for vestigiality is that in comparison to its state in the sister groups the structure exhibits extreme reduction. We considered this criterion met if the structure was reduced to one-third its size relative to adjacent skeletal structures, in comparison with its state in the sister groups

Summary

Introduction

A vestigial structure is a biological structure that has lost a major ancestral function and is usually drastically reduced in size. As early as the eighteenth century, Erasmus Darwin (1791) recognized vestigial structures as evidence for biological evolution, and such recognition continues among today’s biologists and paleontologists (e.g., Prothero, 2007; Hall & Hallgrimsson, 2008; Senter et al, 2015). For such structures Lamarck (1809) used the French words rudiments and vestiges. Charles Darwin (1859) used the term “rudimentary organs.”. Wiedersheim (1895) popularized the use of the term “vestigial” for such structures, and such use continues today Charles Darwin (1859) used the term “rudimentary organs.” Wiedersheim (1895) popularized the use of the term “vestigial” for such structures, and such use continues today

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Conclusion