Sesamoids in tetrapods: The origin of new skeletal morphologies

ABDALA, VIRGINIA; VERA, MIRIAM CORINA; AMADOR, LUCILA; FONTANARROSA, GABRIELA; FRATANI, JESSICA; PONSSA, MARIA LAURA

BIOLOGICAL REVIEWS OF THE CAMBRIDGE PHILOSOPHICAL SOCIETY

CAMBRIDGE UNIV PRESS

Lugar: Cambridge; Año: 2019

0006-3231

Along with supernumerary bones, sesamoids have been frequently considered asenigmatic structures associated to the joints of the skeletal system of vertebrates. Our review of the literature allowed us to propose a dynamic model to account for a considerable part of the skeletal phenotypic diversity: Sesamoids can displace, attach and detach to and from the long bone epiphyses and diaphysis. Epiphyses, apophyses and detached sesamoids are able to transform into each other, contributing to the phenotypic variability of the tetrapod skeleton. This dynamic model is a new paradigm to delineate sesamoids contribution to the skeletal diversity. Herein, we first present a historical approach to the study of sesamoids, discussing the genetic vs. epigenetic theories of their genesis and growth. Second, we explain the dynamic model. Third, we present a state-of-the-art summary of sesamoid literature of the main groups of tetrapods and the veterinary and human clinic contributions, which are the best studied aspects on sesamoids in the last decades. Lastly, we discuss the identity of some structures, which have been usually labelled as sesamoids in spite of the insufficient formal testing on its homology. We also propose a new definition that would help the identification of sesamoids in general. This review is particularly timely, given the recent increasing interest and research activity around the developmental biology and mechanics of sesamoids. With this updated and integrative discussion, we thus hope to pave the way to improve the understanding of sesamoid biology and evolution