Sharks, the fierce and enigmatic predators of our oceans, have a remarkable history spanning half a billion years. Their lineage has produced iconic creatures like the mighty Megalodon, the bizarre Helicoprion with its buzz-saw jaw, and the fearsome Great White shark. How have these creatures managed to endure such an incredibly long time?
John Long, a paleontology professor at Flinders University in Australia, has devoted over 40 years to studying ancient sharks and other fossilized fish. His latest book, ‘The Secret History of Sharks,’ unveils the captivating story of their evolution. Long explains that their success lies in their adaptability and resourcefulness. They are the only group of jawed vertebrates to have survived all five major mass extinction events that have reshaped Earth’s history.
Long highlights that sharks’ survival is not about pre-planning. Instead, their remarkable diversity ensured that some lineages would always be able to weather the storm of extinction. By the Devonian period (419 million to 359 million years ago), sharks had developed a streamlined body plan similar to what we see today. This improved design allowed them to diversify rapidly, making them less vulnerable to future extinction events.
During the Devonian, sharks further diversified, evolving a range of tooth types, including crushing plates, sharp piercing teeth, and even filter-feeding mechanisms before any other vertebrates. This adaptability in their dental development, akin to a ‘Swiss Army knife’ of teeth, allowed them to thrive on whatever food sources were available.
Through his meticulous research, Long has uncovered new insights into the evolution of sharks, many of which were previously unknown. He interviewed leading experts in the field, gathering information about recent discoveries, including exciting new information about the enigmatic Megalodon.
Recent studies using clumped isotope paleothermometry revealed that Megalodon was a warm-blooded creature. This discovery sheds new light on its capabilities, as it allowed Megalodon to venture into colder waters and expand its range significantly. Evidence of Megalodon teeth has been found across the globe, except for Antarctica. This absence has led Long to theorize that whales may have migrated to Antarctica as a refuge from this massive predator, only returning to warmer waters to give birth.
Despite the wealth of knowledge gathered, there are still significant gaps in the shark fossil record. One of the biggest mysteries revolves around the relationship between sharks and placoderms – armored fishes that dominated the Silurian and Devonian periods. A recent discovery in China – a shark-like fish called Shenacanthus – with armor plates and shark-like spines, offers intriguing clues about the evolutionary links between these two groups.
However, the question remains: Did placoderms evolve into sharks by losing their armor, or did sharks evolve armor to become placoderms? This is a question that continues to puzzle paleontologists.
In the book, Long addresses a sobering reality: sharks are facing a new threat – humanity. Current estimates suggest that humans kill between 70 and 100 million sharks annually through the shark finning industry, a cruel practice that involves severing the fins and discarding the living shark back into the ocean to die a slow and agonizing death.
Long urges greater public awareness and education about this devastating practice and emphasizes the need for international collaboration to implement stricter legislation. He advocates for the banning of shark finning and the import of shark fin products, as seen in countries like the UK, to prevent the decimation of these magnificent creatures.
Long’s ‘Secret History of Sharks’ provides a compelling and comprehensive look at the incredible journey of these ancient predators. It not only delves into their evolutionary history but also highlights the dire threat they face in the modern era. By understanding their fascinating past and appreciating their vital role in the marine ecosystem, we can better protect them for future generations.
