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Morphological and functional changes in the vertebral column with increasing aquatic adaptation in crocodylomorphs
Julia L Molnar1, Stephanie E Pierce2, Bhart-Anjan S Bhullar3
1Department of Anatomy , Howard University College of Medicine , Washington, DC 20059, USA ; Structure and Motion Lab, Department of Comparative Biomedical Sciences , The Royal Veterinary College , Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK.
Royal Society Open Science
|December 31, 2015
Summary
Evolutionary changes in crocodylomorph axial skeletons influenced trunk flexibility and stiffness. Early terrestrial species showed unexpected movement limitations, likely due to dorsal osteoderms, impacting aquatic adaptation studies.
Area of Science:
- Paleontology
- Evolutionary Biology
- Biomechanics
Background:
- The evolution of Crocodylia over 200+ million years involved significant changes in morphology, ecology, and locomotion.
- The axial skeleton plays a crucial role in vertebrate locomotion, and its modifications likely contributed to functional innovations in crocodylomorphs.
Purpose of the Study:
- To investigate how osteological range of motion (RoM) and intervertebral joint stiffness changed in the thoracic and lumbar vertebrae of crocodylomorphs with increasing aquatic adaptation.
- To compare the axial skeleton mechanics of a modern crocodile (Crocodylus) with extinct crocodylomorphs representing a spectrum of terrestrial to fully aquatic lifestyles.
Main Methods:
- Utilized three-dimensional virtual models and morphometrics to analyze osteological RoM and joint stiffness.
- Compared modern Crocodylus with extinct taxa including Terrestrisuchus, Protosuchus, Pelagosaurus, Steneosaurus, and Metriorhynchus.
- Experimentally measured trunk flexibility in Crocodylus by sequentially removing osteoderms and soft tissues.
Main Results:
- Results for more aquatic species aligned with predictions, but terrestrial early crocodylomorphs showed unexpected movement patterns.
- The rigid dorsal osteoderms in early crocodylomorphs likely explain the discrepancies in predictions for terrestrial forms.
- Different axial structures influenced dorsoventral versus mediolateral bending in Crocodylus, indicating varied effects of osteoderm and rib morphology changes.
Conclusions:
- The evolution of the crocodylomorph axial skeleton, particularly the influence of osteoderms, significantly impacted trunk mobility and stiffness.
- Understanding these axial changes is key to explaining the evolutionary trajectory of locomotion from terrestrial to aquatic environments in crocodylomorphs.
- Morphological changes in osteoderms and ribs over time differentially affected movement capabilities in various planes.
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