The Modern Day Shark

What makes it?

Morphology

The modern day shark is different from its ancestors and has adapted to their environment in many ways. Sharks live in a marine habatit in which they are submursed in water their whole lives. (27) An example of adaptation is; the shark has evolved from their ancestor the Plesiosaurs because they have grown gills and can breath under water. (22) Also, because of what sharks eat, their teeth have become sharp over time. (18) Many sharks live primarily on meat from other fish like dolphins (for the larger ones) or just large fish (for the smaller ones). (24) Humans are the only preditor to the shark becides other sharks. Another change is the size of the sharks. Sharks have gotten much smaller as compared to their ancestor Megalodons which were 50 feet long. (26) Overall, evolution has modified shark morphology very little except to improve their feeding and swimming mechanisms. Shark teeth are highly diagnostic of species, both fossil and modern. (30) This shows that sharks look increadably different from their ancestors. This is because of how they have adapted to the environment and their habatat.
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Ancestors

Evolution of sharks video (39)

Evolution of Sharks: The World's Deadliest Fish

Fossil Reccord

Because sharks are not made up of bone, (like most animals) and are made up of cartalidge, there is not really a fossil record. However their teeth do make excelent fossils and because of teeth fossils we can predict how large or small sharks used to be, and what they ate. (32) This shows that sharks have devoloped over time based on what they eat and have become smaller as time goes on.
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DNA Analysis

"We investigated the genetic structure of blacktip shark (Carcharhinus limbatus) continental nurseries in the northwestern Atlantic Ocean, Gulf of Mexico, and Caribbean Sea using mitochondrial DNA control region sequences and eight nuclear microsatellite loci scored in neonate and young-of-the-year sharks. Significant structure was detected with both markers among nine nurseries (mitochondrial PhiST = 0.350, P < 0.001; nuclear PhiST = 0.007, P < 0.001) and sharks from the northwestern Atlantic, eastern Gulf of Mexico, western Gulf of Mexico, northern Yucatan, and Belize possessed significantly different mitochondrial DNA haplotype frequencies. Microsatellite differentiation was limited to comparisons involving northern Yucatan and Belize sharks with nuclear genetic homogeneity throughout the eastern Gulf of Mexico, western Gulf of Mexico, and northwestern Atlantic. Differences in the magnitude of maternal vs. biparental genetic differentiation support female philopatry to northwestern Atlantic, Gulf of Mexico, and Caribbean Sea natal nursery regions with higher levels of male-mediated gene flow. Philopatry has produced multiple reproductive stocks of this commercially important shark species throughout the range of this study." (34) This shows that based on where sharks live their DNA is altered. This may be because of the ammount of salt in the water or the size of their prey. Their size would change because they are isolated form other sharks and what they ate was either smaller or bigger. Over time only the smaller or bigger sharks lived because they got enough food; this led to an over all size change in the isolated species. This also applys to the amount of salt in the water. Only the sharks that could live in the slatier water lived on; this led to all the sharks in the isolated species being able to survive in saltier water.

Related Species

For this I am going to zero in on a specific species of sharks. Due to the figures found on http://www.sharks.org/species.html (35) the "Whale Shark" will be the species. Whale sharks live in tropical zones close to the surface and is a member of the Orectolobiforme order. (38) The Stingray is commonly found in the shallow coastal waters of temperate seas. (37) The stingray is related to the Whale Shark because they both do not have eyes on the front of their heads. Also they both live underwater and are flat. The animals also have a similar texture to their skin. (35/37) Because of these things the stingray is related to the whale shark. Another species related to the whale shark is the carpet shark. Carpet sharks live mostly bottom dwelling in shallow to moderately deep warm waters in temperate to tropical zones. They are related to the whale shark because they are mostly flat and their eyes are on the side of their heads. Also they are in the same order as the whale shark (Orectolobiforme). (38) This is why the whale shark and carpet shark are related. Almost all of the whale shark's related species live in temperate or tropical waters like the whale shark itself. These include the Indian, Pacific and Atlantic oceans. (38)