Graduation Year

2023

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Biology

Reader 1

Lars Schmitz

Reader 2

Donald McFarlane

Abstract

Ichthyosaurs are an extinct clade of secondarily aquatic reptiles that lived from 250 to 65 million years ago. Prior research has suggested that ichthyosaurs evolved larger than average scleral rings as an adaptation to prevent damage to the eyes that can occur during fast swimming. To test this assertion, we compared the internal (INT) and external (EXT) scleral ring diameter to the orbit length in 589 species from the 7 following clades: Archosauria, Aves, Dinosauria, Ichthyosauria, Pterosauria, Squamata, and Synapsida. New data points were collected both in person and digitally using a combination of CT scan rendering software in Amira and image measurement tools in Adobe Illustrator. Residual plots showed that ichthyosaurs have larger EXT values and smaller INT values, meaning that they have scleral rings that cover more of the eye than other clades. However, many land-dwelling diurnal squamates also exhibited this same pattern which indicates that the extensive ossification of scleral rings in ichthyosaurs may not be an adaptation to aquatic life. More research is needed to define a potential phylogenetic relationship between squamates and ichthyosaurs.

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This thesis is restricted to the Claremont Colleges current faculty, students, and staff.

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