“Pachyostosis” in aquatic amniotes: a review

Abstract

During the course of amniote evolution, numerous taxa secondarily adapted to an aquatic life. It appears that many of these taxa primitively display "pachyostosis," an osseous specialization characterized by an increase in bone compactness and/or volume. The term "pachyostosis" is used in morphological and histological descriptions to describe what in fact corresponds to different patterns. The aim of this paper is to present the current state of knowledge relative to this adaptation among aquatic amniotes. All the taxa that have returned to an aquatic environment are listed. Moreover, their degree of adaptation to the marine environment, their life environment, and the nature of their "pachyostotic" pattern, when present, are described. This inventory enables the evaluation of the current quality of the data relative to this specialization and provides an indication of the work that remains to be done. The functional consequences of "pachyostosis," and notably its importance for buoyancy control in the context of hydrostatic regulation of the body trim, are discussed and opposed to the requirement of improved swimming abilities in the case of a hydrodynamic mode of trim regulation. Questions are posed about the signification of the polymorphism displayed by this specialization between different taxa, different specimens of the same taxon and different bones of the same specimen, and the problem of quantification of pachyostosis is discussed.

Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru

“…It appeared in all major tetrapods taxa (see also review in [2]), and affects to different degrees either a delimited region (e.g. rostrum of ziphiid whales [3,4]) or much broader parts of the skeleton [2,5]. It is often, but not always, associated with pachyostosis, a hyperplasy of the cortical part of bone shafts that creates a massive and swollen aspect and can spectacularly increase skeletal volume [6].…”

Mesozoic marine reptile palaeobiogeography in response to drifting plates

“…These clades convergently adapted to an aquatic life and exhibit diverse morphologies (see Houssaye, 2009;Fig. 1).…”

Accuracy of mandibular force profiles for bite force estimation and feeding behavior reconstruction in extant and extinct carnivorans

“…As such, the presence of a thickened mandibular corpus may not be exclusively an adaptation for osteophagy but rather an adaptation to sustain greater stresses associated with powerful bites, be it for durophagy or for subduing large prey. Interestingly, a thickened mandibular corpus evolved independently in some aquatic vertebrates as an adaptation for buoyancy or bottom feeding (Domning and Debuffrenil, 1991;Houssaye, 2009;Jones et al, 2013) and not for delivering powerful bites.…”