Thursday, August 17, 2017  

Fossil Shark Teeth of Eastern Virginia

Below the Robert O. Norris Jr. Bridge near White Stone, the Rappahannock River has nearly completed its journey to the Chesapeake Bay. At low tide the river’s shores are mere strands of sand and pebbles that succumb to the rising tide. This twice daily inundation is a beachcomber’s dream, strewing the swash with detritus, some of it eons old. For this is fossil country and while the views up and down the river are  stunning, a fossil hunter’s eyes are cast downward as the ebbing tide reveals the river’s treasures.

Our region’s tributaries are part of the ancient Yorktown Formation that includes the Potomac, Rappahannock, York, James and Piankatank Rivers. Eons ago saltwater seas extended far inland, and sand, silt and clay erosion washing down from the Appalachians provided ideal conditions for fossil preservation.

As sea levels repeatedly rose and fell, fossils were deposited at various layers. The prominent bluffs of the Potomac, stretches of the Piankatank just below Twiggs Bridge separating Mathews and Middlesex Counties, and the shores of the lower Rappahannock are just some of the rich outcroppings containing fossil deposits: extinct shark teeth, whalebones, bivalves and crustaceans.

With each storm or heavy downpour the land releases its deposits into the rivers. Windy days are best, providing enough wave action to uncover and send ashore a variety of fossils. Even a vigorous boat wake may send a fossil shark tooth tumbling ashore.

My introduction to the world of fossil shark teeth began on a quiet sunny morning in early summer. Strolling along a beach with a friend whose own fossil shark tooth collection numbered in the hundreds, Mary’s daily walks along the river rarely failed to uncover a tooth or two. With her eyes calibrated for finding even the tiniest teeth, I resigned myself to being a spectator as she pocketed one after the other. Periodically she would stoop and pick up a promising shape in the shallows, only to discover a twig or stone mimicking the shape of a shark tooth. A ‘tsk” of disgust and she would toss the wayward find back into the river.

Ecstatic over the fragment of 18th century black glass I had just found, I nearly overlooked the large shark’s tooth lying at the high tide line, a gift from a passing boat. Two inches long, pale blue with a gray cusp, I later learned it came from the lower jaw of an extinct Mako shark. Compared to most fossil teeth found in the area, this tooth was a large one and well preserved.

Fossil records suggest sharks have been around for at least 400 million years. Little changed from their ancient ancestors, sharks are a never-ending source of teeth. A shark can have hundreds of teeth in its mouth at any one time, its jaw a veritable conveyor belt that pushes old and damaged teeth out, replacing them with new ones.

“Most of the big sharks can live thirty years or more,” explains Dr. John Musick, Professor of Marine Science at the Virginia Institute of Marine Science. “Sharks shed teeth every two to three weeks over their life span and since they are continuously replaced, one shark can produce thousands of teeth. That’s a great adaptation trait for a predator.” The vast majority of the fossil shark teeth hunters find are shed teeth.

A tooth becomes a fossil when it is buried in sediment soon after being lost from a shark’s mouth. Sediment prevents oxygen and harmful bacteria from reaching the tooth and destroying it. Encapsulated for thousands upon thousands of years, the soft tissue of the tooth dies and the tooth enamel absorbs the color of whatever impurities are in the sedimentary material in which it lies. Unlike a new tooth that is pure white, ancient fossil teeth are dark blue, gray, brown or black, depending on the minerals present during fossilization. Mineral absorption also increases the weight of each tooth so that larger fossil teeth are quite heavy compared to new.

The largest teeth found in Virginia are from the Carcharocles Megalodon, by far the largest sea predator to have ever lived. Believed to have been fifty five to sixty five feet long and weighing more than fifty tons, this forebear to the great white has left behind impressive fossil teeth, some more than seven inches long.

The first question that comes to mind when you find one of these ancient treasures is “What kind of shark did this come from?”

According to Dr. Musick the majority of fossil shark teeth found in this area are from extinct mako, sand tiger and great white sharks. Size, shape, and markings can certainly assist amateur fossil hunters in identifying likely species, but the dizzying array of tooth shapes can seem overwhelming to the novice collector.

Anyone who enjoys watching sensational shark documentaries on television has certainly seen the impressive anterior teeth up close and in living color, but upon closer inspection a shark’s jaw generally contains four functional groups of teeth, each with a specific purpose.

The most impressive are the large and blade-like cutting teeth used to gouge out flesh from large prey. Grasping teeth, large and slender, impale and restrain small prey. Clutching teeth, similar in shape to grasping teeth albeit smaller with shorter crowns, are used to restrain prey and are enormously useful when crushing small armored prey like crabs and lobsters. Finally the crushing teeth exert tremendous compressive forces to dispatch even the toughest prey. It takes an expert or knowledgeable collector to identify the species from which they came, although there are several source books available to assist you.

So where does one go to find these fossil teeth? Most beaches along the rivers are privately owned and in Virginia property lines begin at the low tide mark. Some owners are willing to let you search if you ask permission first and leave their property as you found it. If a private beach isn’t available, eastern Virginia has a wealth of state parks rich in fossil deposits.

Westmoreland State Park extends one and a half miles along the Potomac River, and within its 1,311 acres resides the impressive bluffs of the Calvert Formation, containing strata of sediments rich in fossil history. During warmer weather this park can be heavily over-collected so you may want to wait for cooler weather and smaller crowds. Following a storm out of the northeast can be prime for fossil hunting. Plan a day trip or an extended stay in one of the park’s cabins or campgrounds. Make sure you check with the park’s rangers about the areas open to fossil hunting as some parts of the park and adjoining private property are off-limits.

York River State Park south of Williamsburg is home to the Eastover and Yorktown Formations. Permission must be obtained to keep any fossils found within the park but the search can be well worthwhile as the area has produced not only fossil shark teeth and vertebrae, but sponge, coral, clam, oyster and scallop fossils as well.

If you’ve had little luck finding a suitable site or are reluctant to hunt alone, there are a number of companies offering fossil hunting adventures by foot and by boat. A search of the Web provides a wealth of information about group guided tours, many of which have been granted permission to hunt in areas closed to individual fossil hunters.  Despite their tough outer appearance fossil shark teeth are fragile. Once removed from their natural environment,  they should be carefully preserved to prevent deterioration. Shark teeth should be soaked overnight in warm water, slowly dried out of direct sunlight and placed into protective containers.

A partitioned box used to store jewelry beads and small Ziploc bags found in most arts and crafts stores provide excellent storage for modest collections. But if you have been bitten by the shark tooth bug, you might want to invest in hardware storage boxes with multiple compartmented drawers or keep your eye out for old dental cabinets or map drawers at estate sales or antique shops. At the very least you should record where and when each fossil was found.

If you’ve searched in vain or the great outdoors is not your cup of tea, you can always turn to online auction sites that sell fossil shark teeth. With just your computer and a little time you can obtain a specimen shark’s tooth at relatively affordable prices.

Most fossil shark teeth are neither large nor rare, and it takes patience and a calibrated eye to spot them. Some of the nicest are no larger than the head of a tack and easily overlooked while you eagerly search for something larger. With great variation in size, shape, and color, identifying your find takes a bit of detective work but the results can be quite satisfying.

So slather on some sunscreen, grab a bag and perhaps a shovel or net, and head out on a new adventure. See you on the beach!