Prehistoric Sharks

posted: 04/11/12
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Prehistoric Sharks
Louie Psihoyos/ Science Fiction/Getty Images

Sharks are among Earth's oldest life-forms, having emerged between 455 and 420 million years ago. To grasp how ancient that is, consider that insects, seeds, amphibians, reptiles and flowers were all just a glint in Mother Nature's eye at the time, since they appeared much later. We humans are only around 200,000 years old, meaning that sharks predate us by well over 419 million years. These mighty water dwellers have paid their evolutionary dues, and they more than merit our respect, attention and conservation efforts.

The World's First Sharks

Shark experts theorize that oceans during the later Ordovician period, from 488 to 433 million years ago, must have been teeming with bizarre fish and giant plants that rose from the seafloor. Full skeletons do not exist for the sharks that first swam into this vibrant environment, but tiny fin spines, vertebrae, scales, soft tissue impressions and, most importantly, teeth, provide tantalizing clues as to what these early sharks were like. The first known shark scales come from Elegestolepis. Leonodus was another early shark. It probably lived in shallow bodies of fresh water.

A fast-forward to the Carboniferous period, from 360 to 286 million years ago, leads to an even richer shark fossil record. Many historians refer to this period as the Golden Age of Sharks. During this time, at least 45 different taxonomic families of sharks ruled the world's waters. Among the most memorable was Stethacanthus. Females of this 2- to 3-foot-long species probably resembled today's dogfish sharks, commonly sold today as the "fish" in British fish and chips. Males, however, possessed a dorsal fin with a scaly flat surface that has been variously described as looking like an anvil, an ironing board or a man's hairbrush. The top of the male's head featured another flat surface, covered with small spikes. No one is certain how these features functioned, but they could have been used for defense or in courting the rather dull-looking, but desired, females.

From Buzz Saws to Veils

The vast majority of early sharks were anything but dull, however. The lower jaw of Helicoprion, which lived around 250 million years ago, was covered with saw-like teeth that curled in a spiral underneath the shark's head. Echinochimaera, on the other hand, possessed a yellow and purple Easter bunny-type snout and a back covered with sharp spikes. Orthacanthus, which went extinct just before dinosaurs emerged, had a 10-foot-long body and a head that looked to be all mouth. Double-fanged teeth lined its jaws.

Other ancient oddities included Paleocarcharias, a multi-finned German shark with brown spots all over its body, and the perpetually bug-eyed Symmorium, whose gaping, toothy jaw and bulging eyeballs made it look like it was in a permanent state of horror. Belantsea, on the other hand, possessed veil-like fins that must have swayed gently back and forth as the bright yellow shark moved. Scapanorhynchus, from around 110 million years ago, was a better swimmer than Belantsea, but it too possessed an anatomical oddity. Its enormous snout jutted off the top of its head, leaving beady eyes just over its mouth.

Megaladon— the Mega-Shark

No overview of prehistoric sharks would be complete without Megaladon, believed to have been the largest shark that ever existed. It still holds the record for being the largest known carnivorous fish. On the far left end of its proposed size spectrum, some scientists believe it exceeded 82 feet in length. More conservative theorists stick to around 43 feet. Newer estimates, based on jaw perimeter and tooth size, place it at 60 feet with a body mass of 50 short tons.

Megaladon resembled modern great white sharks, but it was twice as long and carried around 20 times more weight. Its teeth were also three times the size of those found in a great white's mouth. This predator knew how to use them, too. Paleontologists theorize that it hunted like a great white, only with even more aggression. It likely bit directly into a victim's bone with maximum force and then encircled the injured prey, waiting for it to grow weaker and weaker, before making the final kill.

If time travel were possible for all species, an interesting competitive match could have been made between Megaladon, which emerged 16 million years ago before going extinct 1.6 million years ago, and an armor-plated fish known as Dunkleosteus, which came on the scene much earlier, at 415 million years ago, and went extinct around 360 million years ago. Dunkleosteus, a 4-ton death machine, was recently estimated as having a biting force of 11,000 pounds, or more than twice that of a great white. The armored fish supposedly could devour anything unfortunate enough to cross its path; only a monster shark like Megaladon might have challenged its ocean superiority, if the two had shared space on the evolutionary tree of life.

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