Comparative brain anatomy of lamniform sharks (Elasmobranchii: Lamniformes) and its implications to function, behavioral ecology, and evolution
Date of Award
Master of Science (MS)
Eric Norstrom, PhD
Jason Bystriansky, PhD
Kenshu Shimada, PhD
Understanding the diversity of brain morphology is important to understand the evolution of cognitive ability and how ecology and phylogeny have influenced the variation in brain complexity. I examined the morphological variation of the brain in the shark order Lamniformes based on museum specimens and literature. Where I illustrate a wide range of morphological diversity in lamniform brains, my study shows that there is a strong positive correlation between brain size and body size that sharks with a larger brain tend to have a more foliated cerebellum, but that the body weight over brain weight did not correlate with cerebellar complexity. In addition, the brain size is found to be affected by ontogeny where younger individuals tend to have larger brains than older conspecific individuals. I also demonstrate that different sizes of different parts of the brain with different functions reflect different lifestyles. Some ecological specializations are reflected in the brain anatomy of certain lamniforms, such as adaptations to deep-water (Mitsukurina), filter feeding (Megachasma), tail-based prey hunting (Alopias), and thunniform swimming (Lamnidae). My study also shows that more derived lamniform taxa (e.g., Alopiidae, Cetorhinidae, and Lamnidae) have highly foliated cerebellum, where limited foliation is regarded as plesiomorphic. Lamnids have relatively small brain, whereas alopiids have a large brain, where a mid-sized brain can be interpreted as plesiomorphic. My study represents the first investigation into the morphological variation and diversity of the brain focusing on lamniforms and demonstrates how ecological factors such as habitat, diet, and behavior drive brain evolution.
Guzzo, Francesco, "Comparative brain anatomy of lamniform sharks (Elasmobranchii: Lamniformes) and its implications to function, behavioral ecology, and evolution" (2019). College of Science and Health Theses and Dissertations. 335.