Megalodon is thought to be related to mako sharks, porbeagle sharks and other lamniformes (sharks with two dorsal fins, five gill slits and a mouth that extends back beyond the eyes), including the great white.
Since the skeleton of a shark is primarily made up of cartilage, which disintegrates over time, the only megalodon remains we've discovered are serrated teeth and vertebraelike centra. This has left experts with the arduous task of reconstructing megalodon's anatomy based on limited knowledge. But, just as human dental records can be examined postmortem to identify remains, shark teeth can also tell experts enough to identify the species and its size, possible prey, and prey size. Hundreds of megalodon tooth fossils have been found, and they average 6 inches (15 centimeters) in length -- about the size of a human hand. By comparison, great white sharks' teeth average around 2 inches (5 centimeters) long.
Using fossilized teeth, scientists have reconstructed the jaws of the megalodon and discovered that this shark's mouth was a staggering 7 feet (2 meters) in diameter. Based on this reconstruction and additional research, experts believe that this ancient shark had a broad, domed head with a short snout and massive jaws. If the latest reconstruction is accurate, paleontologists believe megalodon was wider than the great white with larger pectoral fins, and could have grown up to 45 to 60 feet (13.7 to 18.2 meters) in length -- about the size of a Greyhound bus.
In addition to the knowledge gained from megalodon teeth, the centra tell their own story. Because sharks are cold-blooded, each year they get growth rings on their vertebrae with the changing of the seasons, just as a living tree does. Experts can easily determine a megalodon's age at death by examining the centra and counting how many rings appear. The color and width of the rings also help determine growth rate; wide, light rings indicate a faster growth than narrow, dark rings. By studying megalodon's tendencies in growth rate and age at death, scientists are able to understand more about sharks' evolution and how to conserve today's shark populations, too.