A Morphological and Histological Comparison of Tooth Serrations between Neoselachian Taxa

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Author:
Irwin, Alexander
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Todd Donald Cook, Thesis Supervisor
Michael A Campbell, Thesis Honors Advisor
Keywords:
Galeocerdo
Hemipristis
Squalicorax
Enameloid
Serrations
Neoselachians
Abstract:
Tooth serrations, present along the edge of the tooth crown in many modern sharks (neoselachians), are sharp projections adapted for cutting the flesh of prey. Each serration consists of an inner dentine core and an outer enameloid layer composed of individual or bundles of fluorapatite crystallites that are orientated in different directions. Several ancient sharks have independently evolved serrations; however, much less is known about the morphology and histology of these dental structures from the fossil record. Using acid etching techniques, sectioning, and scanning electron microscopy, this study performs a systematic comparison of the morphology and tissue composition of serrations in Galeocerdo (tiger sharks), Hemipristis (snaggletooth sharks), and Squalicorax (crow sharks). Galeocerdo cuvier (modern tiger shark) was compared with the extinct tiger shark species G. aduncus (Miocene), G. mayumbensis (Miocene), G. clarkensis (Eocene), and G. eaglesomei (Eocene) and with the closely related Hemispristis curvatus (Eocene), and more distantly related S. kaupi (Late Cretaceous) and Squalicorax pristodontus (Late Cretaceous). The results show strong similarities in histological organization between G. cuvier and the recently extinct G. mayumbensis and less similarities between the earlier G. aduncus, G. clarkensis, and G. eaglesomei. Squalicorax kaupi and S. pristodontus convergently evolved a tissue arrangement similar to that of G. eaglesomei. The results of this study will be used to aid in taxonomic identification and phylogenetic analysis.