Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science in Geology

Department

Geological Sciences

First Reader/Committee Chair

Stuart Sumida

Abstract

This study documents the ontogenetic development of the braincase in Parasaurolophus, a lambeosaurine hadrosaurid dinosaur known for its distinctive cranial crest. Whereas the crest has been extensively examined for its roles in communication and display, the braincase remains less understood, despite its structural and functional relationship with the crest. This research compares the braincase morphology of a juvenile specimen (RAM 14000, "Baby Joe"), a subadult specimen (RAM 17000), and an adult P. tubicen (NMMNH P-25100), to investigate how developmental changes influenced sensory systems, neurocranial architecture, and biomechanical adaptations across ontogeny.

Detailed morphological analysis reveals progressive changes from juvenile to adult stages, including elongation of the basisphenoid and parasphenoid processes, expansion and fusion of the exoccipitals, and anterior migration of cranial nerve foramina. RAM 14000 exhibits a bulbous basioccipital and widely spaced neurocranial elements indicative of early stage neurocranial flexibility. In contrast, RAM 17000 shows an intermediate condition, with a notably taller parasphenoid process and a more angular basisphenoid than either RAM 14000 or NMMNH P-25100, suggesting active remodeling during adolescence. P. tubicen presents the most derived morphology, with a reinforced occipital region, smoothed supraoccipital, and extensive neurocranial integration likely adapted to support a fully developed dorsal crest.

These findings support a peramorphic growth model for Parasaurolophus, marked by accelerated development and exaggeration of adult traits. Comparative data suggest that Parasaurolophus braincase development diverged from that of other lambeosaurines by exhibiting earlier and more pronounced neurocranial changes, including a more rapid development of the frontal and parietal regions and elongation of the supracranial crest. By incorporating both ontogenetic and phylogenetic perspectives, this study provides new insights into how developmental timing and structural adaptation contributed to the unique cranial morphology of Parasaurolophus, particularly in its most morphologically specialized member, P. tubicen.

Download

Share

COinS