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Meet the Sharks
It’s quite hard to imagine a shark without conjuring up images of a scary predator swimming through the murky ocean hunting for its next prey. While some of these awe-inspiring creatures, like the great white, are known to be at the top of the food chain, most sharks take up space at different levels of the food chain.
Closely related to the sting ray and the chimaera, sharks turn up in various sizes. Sharks are really a kind of fish, but instead of bones, their skeleton is made up of cartilage!
Maybe the most surprising fact about sharks is how long they’ve lived on planet Earth!
How long have sharks been around?
The group of families we know as sharks include some of the oldest families on Earth. While some families, like the velvet worms, outdate them, you’d be surprised to know that sharks are not only older than dinosaurs, but even trees!
Since sharks are cartilaginous, the only hard part of their body is their teeth. These teeth sink to the ocean floor as sharks grow out of them and remain as fossils that help to understand the history of these animals. Turns out, the oldest fossilised teeth are over 410 million years old!
These teeth belonged to the species Doliodus problematicus. Of course, the oldest sharks don’t look very “shark-like” by today’s standards—while they did have the cartilaginous skeleton and a shark-like jaw and skull, they also had diamond -shaped scales and spines near their fins.
The first group that we might recognise as sharks, the Cladoselache, evolved 380 million years ago. They had the iconic body shape, the dorsal fins, and the forked tail that we attribute to sharks! Then, around 195 million years ago, sharks evolved their strong flexible protruding jaws.
You may have pieced together that the sharks had their origin nearly 450 million years ago! What that means is that these creatures have lived through four out five of the big mass extinction events. These mass extinction events played a huge role in shaping the climate of the planet and who lived on it. Despite it all, some lineages of sharks have managed to persist.
One such extinction event that took place around 359 million years ago led to the “golden age” of sharks. When nearly 75% of marine life got wiped out during the mass extinction event, several small lineages of sharks managed to survive and reproduce faster, which not only helped them persist but also led to a boom in the diversity of sharks! Talk about resilience!
Cartilage: a strong, flexible connective tissue that protects your joints and bones.
Mass extinction event: a widespread and rapid decrease in the biodiversity on Earth
Lineage: a continuous line of descent from ancestors
Dorsal fin: a fin on the back
Flesch Kincaid Grade Level: 8.4
Flesch Kincaid Reading Ease: 70.6
A Golden Age of Sharks. (n.d.). Retrieved December 28, 2022, from http://www.elasmo-research.org/education/evolution/golden_age.htm
Puiu, T. (2017, January 20). Mindblowing fact of the day: Sharks are older than trees. ZME Science. https://www.zmescience.com/ecology/animals-ecology/sharks-older-trees/
Shark evolution: A 450 million year timeline. (n.d.). Retrieved December 28, 2022, from https://www.nhm.ac.uk/discover/shark-evolution-a-450-million-year-timeline.html
Feehly, Conor. (2022, July 25). Sharks are older than the dinosaurs. What’s the secret to their success? Livescience.com. https://www.livescience.com/secret-to-sharks-success-evolution