Wednesday, March 6, 2013

Megalodon: An ancient shark that makes the Great White Shark look small

Written February 4, 2013, published March 2013.  Photos of teeth from a private collection, all photos by Kathleen Sayce.

Many animals that formerly lived on earth have modern analogs, animals living today that look and behave very like those ancient animals, though they might not be direct descendants. It’s as though the giant cats, bears, wolves, and sharks of the world recur again and again, slightly reconfigured each time. One ancient mega-tooth shark, Megalodon (mega for big, odon for tooth) has a small analog in the great white shark. 

Great White Sharks are big as predatory sharks get today, growing to twenty feet long, weighing up to 4,200 pounds (2.1 short tons). [Some older records of much larger Great Whites are based on inferences of size and not direct measurements.] Body shape and weight of these sharks help estimate the size of fossil Megalodon skeletons. Compared to Megalodon, they are in the second tier for size: Megalodon grew to 67 feet long, and a weight of 114 short tons. 

Megalodon lived from the late Oligocene (28 million years ago) into the start of the Pleistocene (2 million years ago), for 26 million years. Great Whites first appeared during the mid Miocene, so both species overlapped for millions of years. Even when young, Megalodon Sharks were so much larger that Great Whites were probably prey. They ate fish and marine mammals when small, but when more than 40 feet long probably had to shift to whales to get enough protein with each meal. Fossil whale bones have been found with Megalodon tooth marks on them. In some cases, the sharks simply bit the whales in half. Megalodon jaws were up to seven feet wide when open, large enough for a tall man to stand inside, so they could easily catch and eat whales.  Today, a Great White Shark can eat a Harbor Seal in two or three bites. The equivalent for an adult Megalodon was eating a Gray Whale in two or three bites. 

Fossil Megalodon teeth have a characteristic wide triangular shape and serrated edge. All were collected near Bakersfield, Cal. and are in a private collection. 

Megalodon teeth were known long before skeletal fossils were found. Sharks grow many teeth over each life, growing, shedding and replacing them continuously, several hundred teeth per shark. Already hard, teeth easily fossilize, and can be found millions of years later. Megalodon teeth are large, up to seven inches from base to tip, and serrated to improve slicing ability. They turn up in rocks, in marine sediments, and in soils all over the world. Initially they were thought to be fossil dragon or snake tongues, and were called glossopetrae, or tongue stones.  During the late Renaissance a Danish naturalist named Nicolaus Steno correctly identified these as fossil shark teeth. 

From these widespread fossils, found all over the world, we know that Megalodon were cosmopolitan, living throughout the world’s oceans. Like all top predators, their presence determined the structure of the marine communities in which they fed. As they grew, they moved from small to large fish, to marine mammals like seals and porpoises, and then to larger and larger whales. 

This Megalodon tooth is almost five inches wide and tall; the largest teeth known for this species are seven inches tall. Next to it, a fossil Mako shark tooth is two inches tall. Great White Sharks have teeth similar in size to Makos, up to two and one half inches tall. 

The first glacial maximum of the Pleistocene, with shrinking oceans, falling sea levels, and expanding ice sheets, also reduced whale populations due to changes in nutrient cycling that affected the entire food web. These changes left large Megalodon adults starved for food, and impacted the warm shallow seas where juvenile Megalodon lived. Many shallow seas simply drained away as more and more water was locked up on land in continental and montane glaciers. Great White Sharks, being much smaller, with less than one third the length and one fiftieth the body mass of Megalodon, adapted to these changes and survived in colder oceans with smaller prey.   

A small tooth (1.5 inches wide) shows the serrated tooth edge that is distinctive to Megalodon, and which gave it good slashing ability. 

The tooth that was photographed for this article came from California, and was found east of Bakersfield by a private collector. At one time the area was a large shallow sea, and it is known for a large variety of marine fossils. So far as I know, Megalodon fossils have not yet been found in Pacific County. If someone has a Megalodon tooth from this area, I would like to know about it, and I promise to keep your name out of the paper. 

However, we can deduce the historic presence of this great mega-tooth shark without local fossils.  For many millions of years this area was under water, first as deep ocean and later as an ever shallower warm sea.  Megalodon Sharks swam over this part of the planet for millions of years. We see modern Great White Sharks as awesome for their size, speed and predatory behavior. Yet Megalodon was a shark that other sharks avoided, including Great Whites, because they too were food for this top predator.