"Pachyostosis" in aquatic amniotes: a review

Area of Science:

• Paleontology
• Comparative Anatomy
• Evolutionary Biology

Background:

• Numerous amniote lineages have independently evolved secondary aquatic lifestyles.
• Pachyostosis, characterized by increased bone density or volume, is a common adaptation in these aquatic taxa.
• The term 'pachyostosis' encompasses diverse morphological and histological patterns across different species.

Purpose of the Study:

• To provide a comprehensive overview of pachyostosis in aquatic amniotes.
• To catalog taxa that have returned to aquatic environments and describe their pachyostotic patterns.
• To assess the current state of knowledge and identify research gaps regarding this specialization.

Main Methods:

• Inventory of aquatic amniote taxa.
• Description of their degree of marine adaptation and life environment.
• Analysis of the nature and patterns of pachyostosis when present.

Main Results:

• A comprehensive list of aquatic amniotes and their associated pachyostotic features is presented.
• The study highlights variations in pachyostosis across different taxa, specimens, and even bones within a single specimen.
• The functional implications of pachyostosis for buoyancy control versus hydrodynamic swimming are discussed.

Conclusions:

• Pachyostosis is a significant adaptation for buoyancy regulation in aquatic amniotes.
• The polymorphism of pachyostosis suggests complex evolutionary and functional drivers.
• Further research is needed to quantify pachyostosis and understand its diverse manifestations.