An extinct shark about 2.6 million years agoMegalodon was the largest and most dangerous predatory shark ever to exist on Earth. Today, the largest predatory shark is the white shark, it is a man-eating shark. She has more than 400 attacks on a person, a quarter of which have been fatal. In a recent study, scientists discovered that the two most dangerous predators of the deep sea were actually descended from a small, flat shark that lived near the seabed about 165 million years ago.
The oldest ancestor of the white shark
Megalodons and large whites (along with someother sharks) are members of the herring shark group, also known as the lamniform. One of the features that distinguishes these sharks from others is their teeth.
Shark teeth consist of solid mineralizedenamel shell surrounding the core of the dentin. Dentin, in turn, usually consists of two types of tissue: orthodentin, which is limited to the crown of the tooth, and a greater number of bone osteodentin, which is located in the root and sometimes in the crown of the tooth. When osteodentin is additionally present in the crown, it serves to support orthodentin.
During the new computer researchtomography of herring shark teeth showed that in her case osteodentin spreads from root to crown, completely replacing orthodentin, thus remaining the only type of dentin tissue in the tooth.
Having studied the fossil remains of long-extinct sharks, scientists discovered that the only other shark that had the same teeth found was known as Palaeocarcharias stromeri.
Skeleton of a Fossil Shark Palaeocarcharias stromeri
This shark was no larger than a meter in length, andengaged in hunting for small fish, mainly in shallow water, 165 million years ago. She had a flat body that resembled the body of modern carpet sharks. And although for the rest she had nothing to do with herring sharks, she, nevertheless, is now considered their distant ancestor.
"The presence of orthodentin in the teeth is characteristicpractically for all vertebrates - from fish to mammals, including all species of modern sharks, except for herrings, ”says study author Patrick Jombour of the University of Vienna. “The presence of this unique tissue in the teeth of the fossil shark Palaeocarcharias is a serious proof that we discover the most ancient ancestor of the modern white shark.”
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