Comparative Dental Morphology and Histology Between Squalicorax Species

open_access
Open Access
Author:
Olevnik, Lauren
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:
Squalicorax
etching
SEM
serrations
Turonian
Abstract:
Squalicorax is an extinct group of medium to large scavenging sharks. Their vast paleogeographical range covers Europe, Africa, Asia, Australia, and North America spanning from Albian to Maastrichtian of the Cretaceous period, approximately 100 to 66 Ma. The serration pattern and morphology of three Squalicorax species: Squalicorax sp. A, Squalicorax mutabilis, and Squalicorax pristodontus is described. The teeth of Squalicorax sp. A and Squalicorax mutabilis were both recovered from the Turonian Kaskapau Formation in Alberta, Canada. Squalicorax pristodontus teeth were recovered from Maastrichtian phosphate beds of Khouribga, Morocco. Distinct serration and morphological differences are more easily observed for S. mutabilis, and S. pristodontus, particularly from the blade, kerf, and pitch patterns of the teeth. The serrations of the aforementioned species are composed of a triple-layered enameloid microstructure containing an outermost single crystallite enameloid (SCE) layer made of individual hydroxyfluorapatite crystallites. The underlying layer is a bundled crystallite enameloid (BCE) which contains a thicker, parallel-bundled enameloid (PBE) layer made of parallel crystallite bundles and an innermost tangled-bundled enameloid (TBE) which consists of randomly oriented crystallite bundles. Surface etching acid treatments of various durations were used to produce scanning electron micrographs to be able to better examine the histological structures to determine if the internal tissue composition of the serrations varied between the four species. These analyses were comparatively viewed alongside both documented and undocumented species to see if any were conspecific seeing that they originated from the same time period.