SHARK EVOLUTION
Before you proceed to continue reading:
please know this is for a school project and know im not a professional I've done my best to research so this may not be 100 percent accurate
Oldest shark ancestor: Acanthodian it lived 541 million years ago
The Acanthodians looked more fish liked and are one of the oldest ancestors of sharks, there were different types that have had different eye shapes. They’ve had bony spines and all wide fins. There was hardly any rough idea on where they’ve lived asides from being underwater and strictly just underwater. Acanthodians were absolute carnivores/secondary consumers; it's suggested they were zooplankton eaters. It's believed Acanthodian are related to sharks is because truthfully they're more of a fossil fish but that doesn't change on how their body shapes are very simmilar to sharks and seemed very sharklike in general. Acanthodian have had shark like scales and sharks from earlier eras have had spines on their FINS which was also the same for Acanthodians.
2nd oldest shark ancestor: Gladbachus adentatus it lived 385 million years ago
Gladbachus adentatus are another early shark ancestor (yipee) these fellas have lived in the Devonian era. Unfortunately the only way to describe the way they seemed to appear looking more like an average fish. Gladbachus adentatus lived underwater, no they never grew legs and walked on land stop asking please. Gladbachus adentatus were believed to also be carnivores/secondary consumers; unfortunately there was no resources that were found to back up their adaptations to the watery environment they've lived in. Gladbachus adentatus are said to be related to sharks because of their found fossils
3rd oldest shark ancestor: Cladoselache it lived 385 million years ago
oh wow Cladoselache seemed to also exist at the same time as the Gladbuchus adentatus huh? the Cladoselaches lived in the Devonian era. Cladoselaches look somewhat like modern today sharks but not completely. Cladoselache have had more broad fins, bony spines going down to both dorsal fins! Were these guys still underwater? yes absoloutely. As always the Cladoselache were found to be carnivores/primary consumers and were believed to be eating mostly small things one being small ray-finned bony fish. It's shown that Cladoselache were one of earlier sharks to actually have some teeth according to their found fossils (more older sharks did NOT have teeth) Their left over fossils have indicated that they were fast moving and have had heavy blunt jaw plated to crush hard shelled invertebrates also in order for them to survive and adapt
4th oldest shark ancestor: Stethacanthus it lived 298.9 million years ago
Stethacanthus are very cool looking actually. And once again these guys have lived in the Devonian era. their little huge wedge, they had little spikes all over their body to help them swim more efficiently but maybe not as fast. These suckers still chose to live underwater but thats ok if thats what they want then sure whatever. Just like before Stethacanthus was proved to be a shark because of the very very similar characteristics they share with modern sharks except their weird looking dorsal fin what the heck, did I mention these things were secondary consumers? What did they eat? considering its small size it did eat small fish and other small animals down in the sea. (some fossils)
5th oldest shark ancestor: Otodus obliquus it lived 66 million years ago
The Otudus is one of the recent ancestors to be found which have lived in the paleocene era. And for the last time they've never found a reason to go on land so underwater they've stayed. I really don't know what to say about their looks besides they look the exact same as today modern sharks which is huge proof on why they're still related to the sharks we know today but we ALSO can't forget they're related to the megaladon sharks themselves which is a well known as an extinct shark we know about today! And because of being related to the megalodon they've been able to eat foods like them such as these
Timeline
Final thoughts?
Have sharks really change overtime? Yes they have, they've changed surely but incredibely slow (I mean look at the whales who've evolved over 8 million years ) It may not seem as if sharks haven't evolved as much when they really did because of not much of known consumers in their way to disturb them and knowing they're the secondary consumers themselves. I'd like to also add on they've had no other reason to adapt in big ways, even when sharks survived five mass extinctions which is pretty sick. Thank you for taking the time to learn about sharks.
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sharks have to swim all the time nonstop to avoid sinking/dying
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sharks do NOT have bones
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there are more than 1,000 species of sharks!
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sharks dont sleep like we do