Shark
by Dillon R.
Sharks are very powerful and deadly ocean predators. Sharks come in a very wide variety. There is the tiger shark, the sand shark, the nurse shark, the whale shark, and the great white shark, and those are only five of them. The great white shark is probably the most known shark in the modern world. The great white shark has a torpedo-like body, and it has a least 3,000 teeth at one time. This isn’t true for all sharks, but they all have oily livers, a pelvic girdle, they can only swim forward, and their skeletons are made of prismatic endoskeleton calcification instead of bones or cartilage.
First the sharks evolved a backbone and skull, making them vertebrates. Last on the cladogram they evolved a jaw. By evolving a backbone they could gain the ability to swim faster and smoother, and they gained a brain case to protect the brain. Then by evolving the jaw, sharks are able to rip off food easier and get bigger chunks of it.
The shark is most closely related to the animals on the cladogram from Xiphactinus to the Irish Elk. The most advanced trait that they all share is a jaw, because that is the last thing that the shark evolved on our cladogram. The biggest difference is that sharks have prismatic endoskeleton calcification, not cartilage or bones like all the other animals on the cladogram. If you trace all the animals from the Irish Elk to the Xiphactinus down all the branches and nodes, they all meet up at the same node, the same branching point or node where the shark branches off.
The most advanced trait a shark has evolved is a pelvic girdle, but there are more primitive traits before that one. First the prismatic endoskeleton calcification evolved instead of bones or cartilage. Then their rapid tooth replacement was evolved which helped when they lost a tooth; a new one would be replaced the next day. After that their fins evolved to attach to their prismatic endoskeleton calcification. Next they evolved more space between their gills. Those are all the evolutionary traits shown at the AMNH.
Last updated April 7, 2007.