• Sharks are one of evolution's most enduring success stories.
• In fact four hundred and fifty million years ago, sharks and humans shared a common ancestor, making sharks our distant cousins. According to recent research, this is evident in our DNA, since at least one shark species possesses several genes that are nearly identical to those in humans.
• About 350 species are now found worldwide from Arctic to Antarctic waters, including ocean depths. The greatest abundance and diversity occurs in tropical and warm temperate regions.
  Created by: Trevina Joseph April 16th 2008
• The ancestry of sharks dates back more than 200 million years before the earliest known dinosaur.
• Due to their characteristic of having a cartilaginous skeleton, ancient sharks have left behind few clues to enable us to figure out what they were like. Teeth, scales, and the occasional skull or vertebrae are the only ways for us to discover what these ocean beasts were like.
• The oldest shark-like scales date back to the late Ordovician Period, about 455 million years ago during the Paleozoic era,( from what is now Colorado).
• These scales do however, differ from those of modern sharks in several important respects, so not all paleontologists agree that they came from true sharks.
• The oldest undisputed shark scales are about 420 million years old!! (from early Silurian deposits in Siberia).
• The snout in ancient sharks was shorter and rounded, the jaws were located at front; but now snouts are more pointed and the jaws are underneath the head
• Upper jaws of ancient sharks were fixed to brain case at both front and back (that is called amphistylic) but recent sharks' jaws are fixed only at the back of the case (which is called hyostylic)
• Ancient sharks' olfactory lobes were smaller so they had a less developed sense
  of smell than the recent shark species
• The teeth of the early sharks were smooth edged and multi-cusped
  but now they are single cusped.
• The pectoral fins were triangular, broad, and rigid (not flexible) but recent sharks have much more flexible, narrow, and more agile pectoral fins
• The backbone had simple vertebrae that did not construct a single column.
  More modified sharks have fewer complex vertebrae but they do make up a spinal column
• The actual length of the megalodon which is the oldest recorded shark was about 43 feet. The jaws were six feet across, Weighed about 48 tons, The largest megalodon based on teeth was about 52’. The largest great white ever recorded was only 23 ½’ and only 2.3 tons. So try to image a shark two times as big as the Great White!
• The extinction of these ancient sharks came about because of environmental changes, shortage of habitat (such as widespread cooling, and shifting of tectonic plates), and a shrinking food supply was also a factor because of the same reasons listed above.

Source of information: Martin, R. Aidan.  2003.  Copyright and Usage Policy.  World Wide Web Publication, www.elasmo-research.org/copyright.htm

Picture Source:Chris Fallows/apexpredators.com