Orbit size and estimated eye size in dinosaurs and other archosaurs and their implications for the evolution of visual capabilities

ABSTRACT

Vision is one of the most important senses for animals, allowing them to interact with their environment and with further implications for evolutionary histories. However, relevant soft tissues, such as the eye and associated structures, are not preserved in fossil vertebrates, limiting our knowledge of their visual capabilities. Here, we quantified absolute and relative orbit size for 400 species of dinosaurs and other extinct archosaurs using linear measurements of the preserved skeletal elements as a proxy for visual capabilities. Our results demonstrate that the orbit makes up on average 20% of skull size with a strong and consistent correlation across all sampled groups. This trend is largely independent of temporal distribution, species richness, and phylogeny. In fact, relative orbit size is narrowly constrained and did not surpass 45% of skull size, suggesting physiological and functional controls. Estimated eye size was found to be absolutely larger in herbivores, whereas carnivores tended to have smaller eyes absolutely and compared with skull size. Relatively large eyes only occurred in small-bodied species and vice versa. However, eye size alone was not sufficient to discriminate between different activity patterns or to characterize visual capabilities in detail.

ACKNOWLEDGMENTS

J. Marugan-Lobon is thanked for helpful comments on an earlier version of the manuscript. D. Cerio and K. Chapelle provided constructive reviews which considerably improved the manuscript.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

AUTHOR CONTRIBUTIONS

SL designed the study, supervised undergraduate students, prepared the manuscript and collected additional data. EMD helped with species richness analyses and collected additional data. CMB helped with supervision of undergraduate students and checked data. SL, EMD, and CMB contributed to the creation and writing of the final manuscript. All other authors collected data as part of an undergraduate module at the University of Birmingham.

SUPPLEMENTARY FILE(S)

Supplementary data. Species list_measurements_references.xlsx

Supplementary Table 1: ANCOVA results for major archosaur groups

Supplementary Table 2: ANCOVA results for major dinosaur groups