RESEARCH ARTICLE
Orbital soft tissues, bones, and allometry: Implications for the size and position of crocodylian eyes
Donald Greene Cerio,
Lawrence M. Witmer,
Corresponding Author
Donald Greene Cerio
Department of Biological Sciences, Ohio University, Athens, Ohio, USA
Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, Ohio, USA
Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, USA
Correspondence
Donald Greene Cerio, Center for Functional Anatomy & Evolution, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Email: [email protected]
Contribution: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Software, Visualization, Writing - original draft, Writing - review & editing
Search for more papers by this authorLawrence M. Witmer
Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, Ohio, USA
Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, USA
Contribution: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Visualization, Writing - review & editing
Search for more papers by this author
Donald Greene Cerio,
Lawrence M. Witmer,
Corresponding Author
Donald Greene Cerio
Department of Biological Sciences, Ohio University, Athens, Ohio, USA
Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, Ohio, USA
Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, USA
Correspondence
Donald Greene Cerio, Center for Functional Anatomy & Evolution, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
Email: [email protected]
Contribution: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Software, Visualization, Writing - original draft, Writing - review & editing
Search for more papers by this authorLawrence M. Witmer
Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, Athens, Ohio, USA
Ohio Center for Ecology and Evolutionary Studies, Ohio University, Athens, Ohio, USA
Contribution: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Visualization, Writing - review & editing
Search for more papers by this authorAbstract
Although the visual system of crocodylians has attracted interest regarding optical parameters and retinal anatomy, fundamental questions remain about the allometry of the eyeball and whether such scaling is the same across all crown groups of crocodylians. In addition, anatomy and identities of adnexal soft tissues that interact with the visual system are not well understood in many cases. We used contrast-enhancing iodine stain and high-resolution micro-computed tomography to assess the anatomy of orbital soft tissues, including extraocular muscles and glands, in crocodylians. We also used regression analysis to estimate the allometric relationship between the bony orbit and eyeball across Alligator mississippiensis and Crocodylus niloticus for the first time. Results revealed tight, negatively allometric relationships between the bony orbit and eyeball. Notably, the eyes of C. niloticus were larger for a given orbit size than the eyes of A. mississippiensis, although the slope of the relationship was no different between these two crown crocodylian groups. Among the findings from our anatomical study, new details were uncovered about the homologies of muscles of the abducens complex. In particular, M. rectus lateralis of crocodylians is revealed to have a more complex form than previously appreciated, being adhered to the tendon of the nictitating membrane, which may be apomorphic for Crocodylia. Our calculation of the orbit-eyeball allometric relationship and study of the adnexal soft tissues of the crocodylian visual system, in combination with previous work by other teams in other crown saurian clades, is a critical, formerly missing, piece in the Extant Phylogenetic Bracket for restoring the visual apparatus of extinct crocodyliforms and other archosauriform groups.
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