Original photo by mkurtbas/ iStock
Some species of trees that line city streets predate the dinosaurs by millions of years, but when it comes to the truly ancient, you need to look to the oceans. Sea-dwelling creatures have a many-millions-of-years head start on any terrestrial life-forms. Take, for instance, the shark: This apex predator of the sea has been stalking the world’s oceans for upwards of 450 million years. Meanwhile, the very first forests filled with Earth’s very first trees, in the genera Wattieza and Archaeopteris, likely didn’t sprout on land until the mid-Devonian period some 385 million years ago. However, it’s worth noting that the animals some scientists consider the first “sharks” likely didn’t look like the magnificent predators of today. First appearing in the Late Ordovician, these creatures sported sharklike scales, but likely didn’t yet possess the species’ most memorable trait — a terrifying set of teeth.
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It's a fibSharks are old, but the world’s oceans are home to some truly ancient species. Jellyfish, for example, are thought to be at least 500 million years old, and scientists have found fossils of dendrogramma — a mushroom-like deep-sea animal — that are 560 million years old.
Surviving that long as a species is no easy feat. Only a few million years after the shark’s appearance on the world stage, these proto-sharks (along with the rest of life on Earth) suffered through the Late Ordovician mass extinction. This event was the first of five major extinction events in Earth’s history, and sharks survived them all; not even trees can add such an impressive accolade to their resume. So the next time you cross paths with a shark, whether behind the glass of an aquarium or on screen in the act of devouring the residents of Amity Island, don’t forget to marvel at this amazing animal’s incredible story of survival.
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The ______ geologic period some 359 million years ago is known as the “golden age of sharks.”
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The Carboniferous geologic period some 359 million years ago is known as the “golden age of sharks.”
Marine biologists age sharks in a manner similar to how arborists age trees.
Arborists use a technique called dendrochronology, or counting tree rings, to estimate a tree’s age. Every year, trees put on new growth near their bark, which over time forms predictable concentric circles — a timeline of their lives. In a strange biological plot twist, sharks do much the same thing. Similar to a tree’s trunk, sharks also put down new layers of material on their vertebrae. Unlike the bony bits that form our spine, a shark’s vertebrae are made out of cartilage (in fact, sharks don’t have any bones at all). Although counting the cartilage layers is helpful in getting a snapshot of a particular shark’s life, these layers can be affected by many things, including food shortages and health; plus, older sharks seem to stop putting on new rings entirely. That means counting these vertebrae rings only provides a ballpark estimate of a shark’s timeline. For some species of shark, including the incredibly long-lived Greenland shark, scientists use carbon dating of the proteins embedded in the shark’s eyes from birth to capture a more accurate age.
Darren Orf lives in Portland, has a cat, and writes about all things science and climate. You can find his previous work at Popular Mechanics, Inverse, Gizmodo, and Paste, among others.
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