7 Facts about sharks

7 Facts about Sharks

1. Sharks do not have bones.

Sharks use their gills to filter oxygen from the water. They are a special type of fish known "elasmobranch", which translates into fish made of catilaginous tissues—the clear gristly stuff that your ears and nose tip are made of. This category also includes rays, sawfish, and skates. Their cartilaginous skeletons are much lighter than true bone and their large livers are full of low-density oils, both helping them to be buoyant. 

Even though sharks don't have bones, they still can fossilize. As most sharks age, they deposit calcium salts in their skeletal cartilage to strengthen it. The dried jaws of a shark appear and feel heavy and solid; much like bone. These same minerals allow most shark skeletal systems to fossilize quite nicely. The teeth have enamel so they show up in the fossil record too.

2. Most sharks have good eyesight.

Most sharks can see well in dark lighted areas, have fantastic night vision, and can see colors. The back of sharks’ eyeballs have a reflective layer of tissue called a tapetum. This helps sharks see extremely well with little light.

3. Sharks have special electroreceptor organs.

Sharks have small black spots near the nose, eyes, and mouth. These spots are the ampullae of Lorenzini – special electroreceptor organs that allow the shark to sense electromagnetic fields and temperature shifts in the ocean.

4. Shark skin feels similar to sandpaper.

Shark skin feels exactly like sandpaper because it is made up of tiny teeth-like structures called placoid scales, also known as dermal denticles. These scales point towards the tail and help reduce friction from surrounding water when the shark swims.

5. Sharks can go into a trance. 

When you flip a shark upside down they go into a trance like state called tonic immobility. This is the reason why you often see sawfish flipped over when our scientists are working on them in the water.

6. Sharks have been around a very long time.

Based on fossil scales found in Australia and the United States, scientists hypothesize sharks first appeared in the ocean around 455 million years ago.

7. Scientists age sharks by counting the rings on their vertebrae.

Vertebrae contain concentric pairs of opaque and translucent bands. Band pairs are counted like rings on a tree and then scientists assign an age to the shark based on the count. Thus, if the vertebrae has 10 band pairs, it is assumed to be 10 years old. Recent studies, however, have shown that this assumption is not always correct. Researchers must therefore study each species and size class to determine how often the band pairs are deposited because the deposition rate may change over time. Determining the actual rate that the bands are deposited is called "validation".