Phylogeny Of Sphyrna-Hammerhead Sharks

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Phylogeny of Sphyrna- Hammerhead Sharks
INTRODUCTION
I will be investigating the phylogenetic history of Sphyrna, a genus of hammerhead sharks. The eight species that fall under this genus are Sphyrna corona (scalloped bonnethead), Sphyrna gilberti (Carolina hammerhead), Sphyrna lewini (scalloped hammerhead), Sphyrna media (scoophead), Sphyrna mokarran (great hammerhead), Sphyrna tiburo (bonnethead), Sphyrna tudes (smalleye hammerhead), and Sphyrna zygaena (smooth hammerhead). Hammerhead sharks are noted to be one of the most unique looking organisms in the ocean and are easily distinguished by their cephalofoil, or “hammer” shaped head by which they are named (CITE). Sharks in general having a rich evolutionary history because they have been
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These ancestral species ultimately evolved and diverged into the various lineages of sharks we are familiar with today. Hammerhead sharks are actually considered to be a relatively newer species, with fossilized teeth found in deposits that date back to just 35 to 50 million years ago. In fact, Sphyrna gilberti, the Carolina hammerhead, was just recently identified and added to the genus in 2013, so it is possible that new species of hammerhead sharks still remain undiscovered. I have chosen to dive into the phylogeny of Sphyrna because these sharks are beautiful, mysterious, and they represent the destructive relationship humans have with the oceans. In light of the fact that sharks have thrived for millions of years, and survived cataclysmic extinction events, their existence is being jeopardized due to human impact on their populations and habitat. Several of the identified species of Sphyrna are currently listed as vulnerable or endangered, and populations are rapidly declining along with many other species of sharks. Sphryna lewini, scalloped …show more content…
In order to produce an accurate supertree, he applied morphological data regarding the evolution of the cephalofoil and he examined the likely adaptive implication of this unique hammerhead morphology. Cavalcanti discussed that the cephalofoil allows better maneuverability in the water by providing hydrodynamic lift, similar to the aerodynamic lift of an airplane cruising through the troposphere. Another hypothesis of the significance of the cephalofoil is that it potentially enhances the sensory performance of the shark by placing the spacing sensory structures at the lateral aspect of the head. The author suggests that understanding the evolution of the cephalofoil can be achieved by using morphological and molecular data in a comparative approach to generate an extensive phylogenetic analysis of Sphyrna, and ultimately a

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