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Devonian Tides chapter 3: First Sharks

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Period: Late Devonian (Late Famennian)

Date: 360,000,000 BC

Location: Northern Euramerican coast





Cladoselache, one of earliest known forms of Shark, has just appeared in the Late Devonian. Up to six feet long and at first glance not so very different from the Sharks of the future, it has wide pectoral fins that flare out from the front of its body, helping it maneuver with pinpoint accuracy. In the final lunge for prey, mainly smaller fish, it is powered by a deep forked tail sweeping from side to side. Its body is topped by two dorsal fins, a bladelike structure positioned in front of each of them, a feature that will not often be seen in Sharks of the distant future. There are other more subtle differences too.
Sharks typically have a tooth factory in their mouths: a system like a conveyor belt in the gums that keeps bringing new sharp teeth to replace blunt or broken ones. In the distant future, some species, like the 11-foot-long Lemon Shark of the Cenozoic, will go through 10,000-30,000 teeth in their lives. Cladoselache does not have such a sophisticated system and its teeth can sometimes be worn down to stubs. Also, its jaws are weak and poorly developed compared to those of future Sharks. The basic Shark design has been pretty good right from the start back in the Late Silurian, but over 400 million years tiny improvements such as more resilient teeth and more effective streamlining shall enhance their ability to hunt and feed in the distant future.
In the Devonian seas, however, there are “off the wall” Sharks and other "off the wall" Cartilaginous Fish, unlike any others coming before or after them. One of the strangest is Stethacanthus, a Holocephalian about 2.3 feet long. The males of this extraordinary genus and other Stethacanthids have a dorsal fin in the shape of an anvil or ironing board adorned with a brush of spike-like enlarged versions of dermal denticles along the flattened top, and the Holocephalian's head as well. This "tooth"-covered "pedestal" is used to impress females during courtship.
Sharks and other Cartilaginous Fish are always mesmerizing. However, a few courting Stethacanthus near the reef right now suddenly skedaddle. Why? Because of a giant that with one snap could slice a small Shark or other basal Cartilaginous Fish in two. A Dunkleosteus has arrived on the scene.

To Be Continued
Chapter 3 of Devonian Tides from the Chased by Sea Monsters: Prehistoric Predators of the Deep companion book.

CBD/SM (c) BBC

Companion Book (c) Nigel Marvin & Jasper James
© 2015 - 2024 WWCB
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