Sharks are arguably the oldest family of large animals still alive, with the oldest accepted shark fossil being about 420 million years old, predating the dinosaurs, land animals, and even land plantlife. Sharks as a group have survived four major mass extinctions, each of which had killed at least 70% of all species then living on the planet. Sharks have a great sense of smell, able to detect blood in a concentration of one part per million (for every drop of blood, there are 1 million drops of water), and they have another sense called electroreception, which allows them to detect Earth’s magnetic field…and any movement of nearby prey. Only four shark species (great white, tiger, bull and oceanic whitetip) produce a significant number of fatal shark attacks. Sharks in general, and those four in particular, are the top predators of their environment, and like many other natural hunters, are curious of unfamiliar creatures (read: humans). However, they lack any means to explore the unknown other than their mouth, which can explain some shark attacks considering humans are generally not sufficient prey to warrant feeding as a reason to attack. On average, there is less than one death from a shark attack each year while there are, on average, forty deaths from lightning strike. Finally, the eggs of the grey nurse shark hatch inside the mother and when the first embryo develops, it eats its sibling’s embryos and any unhatched eggs. Talk about sibling rivalry.
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