This is one of the most common questions that I am often asked. Here is what my good friend, palaeontologist Dr. Gilles Cuny of the Geological Museum of Copenhagen has to say:
“The first fossil sharks appeared 430 million years ago, and until the end of the Devonian, 375 million years ago, they showed a rather low diversity and success. But at the end of the Devonian, a major mass extinction event in the history of life wiped all the armoured fishes (the placoderms, the ruling fishes at the time) out from Earth’s seas.
All the placoderms disappeared, but not the sharks who, freed from their competitors, diversified themselves to reach a kind of golden age in terms of success and diversity until the end of the Permian, 251 million years ago. At that time, the most dramatic mass extinction event in the history of Earth occurred, with the disappearance of nearly 95% of the known number of animal and vegetal species.
But again, the sharks survived pretty well this terrible event, and several lineages crossed the boundary (Eugeneodontiformes, large sharks with enlarged symphysial tooth rows, freshwater eel-shaped Xenacanthiformes, the rather unspecialized Ctenacanthiformes and Hybodontiformes, and the first modern day sharks, the Neoselachii, which appeared just before this extinction).
At the end of the Triassic, 200 million years ago, time of another mass-extinction, only the Hybodontiformes and the Neselachii, as well as the Chimaeras, were still around, but just after the end-Triassic mass extinction event, the Neoselachii started to diversify again and the first modern looking sharks appeared (bullhead, six and seven gills, and blind sharks).
At the end of the Cretaceous, 65 million years ago, another mass extinction made the dinosaurs and numerous other animals to disappear, including the Hybodontiformes sharks. This was most likely due to the impact of a huge meteorite on Earth. The Neoselachii were severely hit (84 % of the known species at the time disappeared, but only 17% of the families), but they survived, as well as the Chimaeras, (again, this was their third mass extinction events since their appearance on Earth) and diversified to their actual level of diversity.
We know of about 556 different species, only 3 are considered high risk to humans.
Sharks are top predators in the food chain – they help keep our sea balanced and healthy.
80% of the Shark species do not grow over 2 metres.
The largest is the Whale Shark (Rhincodon typus) that grows to about 18 metres.
Sharks take a long time to reproduce
Is this female Bull shark (Carcharhinus leucas) about to become a Mamma
did she just have a good meal?
Sharks can have as many as 15 rows of teeth, all lined up behind each other.
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