The text is a detailed exploration of the diverse and fascinating world of sharks, particularly focusing on their deep-sea adaptations. It begins by noting that sharks have dominated the oceans for 450 million years, during which they've evolved into a wide array of species.
Sharks near the ocean's surface, such as blue sharks, makos, and great whites, exhibit similar features, including streamlined bodies and a bluish-grey color for blending into their environment. However, the deep-sea sharks are more peculiar and otherworldly.
The text delves into the evolutionary history of sharks, tracing it back to the late Ordovician period, 450 million years ago. It mentions that primitive sharks evolved in various ways, with one group diverging to become the alien-like chimera relatives of true sharks. By the Early Jurassic period, 195 million years ago, the oldest known order of modern sharks, the hexanshiforms or six-gill sharks, had emerged.
These sharks evolved slender, fast-moving bodies and flexible protruding jaws, allowing them to eat prey larger than themselves. Many sharks today have changed immensely since the Jurassic period, but the few that remain unchanged, like the frilled shark and the bluntnose sixgill shark, appear peculiar in comparison.
The text then discusses the adaptations of deep-sea sharks, explaining that in the depths, there is less dissolved oxygen present in the water. This suggests that for six-gill and seven-gill sharks, it is advantageous to have more gill slits so they can absorb the oxygen they need more efficiently.
The text also highlights that the deeper dwelling sharks tend to be far larger, a phenomenon known as deep-sea gigantism. This is because being larger means they lose less energy as heat in the nutrient-poor depths.
The feeding habits of deep-sea sharks are also different from shallower species. While makos and great whites rely on speed and agility to hunt down fast-moving prey, deep-sea sharks must be opportunistic and depend largely on carrion.
The text concludes by stating that deep-sea sharks are unique in the lightless, high-pressure, and nutrient-poor depths. They adopt more ancient adaptations such as more gill slits, flabbier bodies, and larger sizes. This underpins a distinct difference between these deeper species and sharks of the shallows, which have evolved differently to become smaller and faster.
1. Sharks have dominated the oceans for 450 million years, providing them with ample time to adapt and diversify into various species.
2. Many sharks have adapted to life as apex predators at the top of the food chain in the open ocean.
3. Some shark species, such as the great white shark, have adapted to life in the open ocean.
4. Sharks are highly specialized predators, demonstrating an array of adaptations to survive various ocean habitats.
5. Pelagic sharks like blue sharks, makos, and great whites exhibit similar features, such as streamlined bodies and bluish-grey coloring to blend in with their environment.
6. Sharks of the depths are often more peculiar and otherworldly than their surface-dwelling counterparts.
7. The evolutionary history of sharks possibly dates back to the late Ordovician period, 450 million years ago.
8. A group of cartilaginous fish diverged 420 million years ago to become the alien-like chimera relatives of true sharks.
9. By the early Jurassic period, 195 million years ago, the oldest known order of modern sharks, the hexanshiforms or six skill sharks, had emerged.
10. These sharks evolved slender, fast-moving bodies and flexible protruding jaws, allowing them to eat prey larger than themselves.
11. Many sharks found in our oceans today have changed immensely since the Jurassic period, with a few remaining unchanged as living fossils.
12. These living fossils have six or seven gill slits instead of the usual five found on most sharks.
13. The frilled shark is an example of a shark with six or seven gill slits.
14. Many of these more ancient sharks, including both the hexanshi forms and the squaloforms, now seem to inhabit the deeper regions of our oceans.
15. In the depths, there is less dissolved oxygen present in the water, suggesting that for six skill thrilled and seven kill sharks, it is advantageous to have more gill slits.
16. The large eyes of six skills is also an advantage, allowing them to take in as much light as possible.
17. The deeper dwelling sharks tend to be far larger, such as the Greenland shark, which grows to 24 feet or 7.3 meters long.
18. The Greenland shark has evolved to live its life in slow motion, with a highly slowed metabolism that allows it to go for very long periods without eating.
19. The feeding habits of deep sea sharks are quite different from shallower species. While makos and great whites rely on speed and agility to hunt down fast-moving prey, deep sea sharks must be opportunistic and depend largely on carrion.
20. The megamouth shark is one of the largest shark species on the planet and is a filter feeder preying on zooplankton at the surface during the night and returning to the depths during the day.
21. The deep sea is a different world to the surface waters where food is plentiful and survival is less of a challenge for a predator.