Ancient Sharks and Crocodiles’ Nemesis: Man
Since ancient times, people have feared sharks and crocodiles. But how long have these two species actually been on earth and how did they evolve? Crocodiles and sharks have one thing in common: the fact that they have remained completely unchanged for hundreds of millions of years of evolution. It is true, roughly speaking, that if a modern human being could have taken a swim in a river or in the open ocean, 150 million years ago, he would immediately have recognized that animal as a crocodile or as a shark, but there are many substantial differences in their habitat, diet, morphology, size and weight among the various genera which have marked the evolutionary history of these creatures.
Carcharocles megalodon collection from the Gatun Formation (CC BY-SA 2.5)
Sharks Oldest Creatures On The Planet
Sharks are considered among the oldest creatures that have ever lived on this planet. The fossil remains of these animals are about three times older than those of dinosaurs, and almost a hundred times more archaic than the entire evolutionary path followed by the genus Homo itself. The family tree of the Chondrichthyes stands proudly in the long path of natural history for a time span of about 400 million years. Primitive forms of sharks swam sinuously in rivers and early oceans, even before the insects took flight and even long before the plants had actually colonized all the continents.
The origin of sharks is even more obscure than that of most other groups of animals, for they have left very little evidence of their existence. Cartilage does not preserve as fossil as a rule, so most of the evidence of the ancient shark-like fish rests upon their teeth.
Mitsukurina owstoni. A new goblin shark, Scapanorhynchus jordani, from Japan. (Public Domain)
Who Were The Sharks?
The seas of 500 million years ago were certainly different from modern ones, even in their chemistry. In the Silurian period, some 450 million years ago, the first shark-like creatures appeared. This kind of fish were the spiny sharks, they were not true sharks at all. These animals differed from the early jawless fish in having jaws and bone set in the skin of the gill openings and the ‘shoulder’ area. Their skeletons comprise of cartilage (bone has not grown into the cartilage, as in the higher vertebrates).
These early sharks had eyes set well forward on the head and a lateral line system much the same as that of modern sharks. In 1997, in Canada, the scientist Randal Miller and his team discovered a fossil fish about 30 inches (76 centimeters) long, which was dated 409 million years old. The fossil was called Doliodus probelematicus, one of the earliest sharks. The shark was well preserved in its brain case, scales, calcified cartilage, long spines and pectoral fins.
