Origin of the unique ventilatory apparatus of turtles

Department of Earth Sciences, Denver Museum of Nature and Science, Denver, CO, USA
Department of Veterinary Clinical Sciences, Louisiana State University, Baton Rouge, LA, USA
Karoo Paleontology, National Museum, Bloemfontein, South Africa
University of Zurich, Zurich, Switzerland
Institut für Zoologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY, USA
Evolutionary Studies Institute, University of Witwatersrand, Johannesburg, South Africa
Department of Vertebrate Zoology, Smithsonian Institution, Washington, DC, USA
DOI
10.7287/peerj.preprints.1128v1
Subject Areas
Evolutionary Studies, Paleontology, Zoology
Keywords
turtle, lung ventilation, turtle shell
Copyright
© 2015 Lyson et al.
Licence
This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ PrePrints) and either DOI or URL of the article must be cited.
Cite this article
Lyson T, Schachner ER, Botha-Brink J, Scheyer T, Lambertz M, Bever G, Rubidge B, de Queiroz K. 2015. Origin of the unique ventilatory apparatus of turtles. PeerJ PrePrints 3:e1128v1

Abstract

Background. The turtle body plan differs markedly from that of other vertebrates and serves as a model system for studying structural and developmental evolution. Incorporation of the ribs into the iconic turtle shell negates the rib movements that effect lung ventilation in the majority of air-breathing amniotes (the clade encompassing mammals, lizards, turtles, birds, and crocodilians). Instead, turtles have a novel abdominal-muscle-based ventilatory apparatus whose evolutionary origin remains a mystery. Methods. Here we show through broadly comparative anatomical and histological analyses that the earliest stem-group turtle form the middle Permian (260 mya), Eunotosaurus africanus, has several turtle-specific lung ventilation characters: rigid ribcage, inferred loss of intercostal muscles which drive costal ventilation in all other amniotes, and histological correlates for the primary muscle, M. transverses, used in exhalation. Results. Our results place the origin of the unique lung ventilatory apparatus of extant turtles shortly after the divergence of turtles from other reptiles and approximately 50 million years before the oldest known fully developed shell. Discussion. These data indicate that it was an easing of structural constraints through division of function (divergent specialization) between the ribs and abdominal musculature that facilitated the evolution of both the novel turtle lung ventilation mechanism and the turtle shell.

Author Comment

This is an abstract that has been accepted in Nature Communications (DOI: 10.1038/ncomms6211) and for the 5th Turtle Evolution Symposium.