Evolution

Sharks are one of the very few species known to have existed 450 million years ago, even before the dinosaurs. They still continue to exist, however because of humans are now an endangered species.

Prehistoric sharks

The oldest existing evidence of pre-historic sharks are "shark like scales", these fossils are predicted to be from 400 million years ago, during the late Ordovician period. Pre-historic sharks are also believed to have looked very similar to how they do today, which makes sense since they are the top of the marine food chain and have had a reason to drastically evolve. During the late Miocene epoch period, sharks started to spread out to different climates and regions, which is why we have different types of sharks currently. Bull Sharks specifically are speculated to have evolved from an extinct shark called Carcharhinus priscus 11 million years ago. They share this common ancestor with the tiger shark, lemon shark and hammerhead.

Bottle neck

The reason why Bull Sharks are able to breath in freshwater, as mentioned earlier in the respiration page, is because they experienced a bottle neck during the ice age. A bottle neck is where a random event kills off a large percent of the population, sometimes leading to a genetic mutation. The event for Bull Sharks is unknown but did cause cause a genetic mutation related to osmoregulation. These genes were favored over others, leading to an increased population of the freshwater breathing bull sharks we know today.

Image from New York Times article of Bull Shark found in golf course pond Australia:

Page updated

Google Sites

Report abuse