FOSSILS OF CALVERT CLIFFS

From a flyer by Wallace L. Ashby, illustrated by Mary A. Parrish

Calvert Cliffs is located in the largest fossil-bearing deposit of Miocene marine sediments exposed on the East Coast of North America -- the Calvert Cliffs of Maryland. Most of the shells and bones on our beach are fossils Shark teeth and whale vertebrae are prized finds. Rarer specimens include almost complete skeletons of whales and porpoises, bird bones, and remains of land mammals such as mastodon, peccary and small Miocene horses.

These sediments were laid down 10 to 20 million years ago during the Miocene Epoch, when the Atlantic Coast was repeatedly submerged beneath the sea. Studies of fossil animals and plants indicate that in those times, a warm shallow ocean covered this area. Cypress swamps lined the shore. A river wound slowly toward the sea through sand dunes dotted with scrub oak and pine. The climate was somewhat warmer than now. Shells and bones of dead animals sank to the bottom of the sea and were buried in sand and mud, building up over many thousands of years layer upon layer of fossil deposits. Millions of years later, the ocean retreated and what once was sea bottom is now exposed in the cliff face.

Calvert Cliffs extend for more than 30 miles from just north of Chesapeake Beach to Drum Point, rising in places to more than 100 feet in height. Three major intervals of deposition are represented. Sediments deposited during the earliest interval make up the Calvert Formation, which includes the bluish clay the lowest one-fourth of the cliff in the vicinity of Scientists' Cliffs. The Choptank Formation, deposited later, includes the yellow sands and clays in the higher levels of our cliffs. The youngest formation, the St. Mary's, lies farther south; it isn't found at Scientists' Cliffs. The formations dip toward the southeast at an average rate of about 11 feet per mile.

The cliffs are continually eroded by wave action which undercuts the base, by landslides and by storms and frost. Fossils falling into the surf are tossed around, cleaned, and then cast back on shore. Virtually all the shark teeth and the fossil bones and shells found on the beach wash or weather out of the cliffs.

Marine Mammals. The Calvert Cliffs deposits are among the world's richest in fossil whales and porpoises. About two dozen kinds have been identified including sperm whale, shark-toothed porpoise, both long and short beaked porpoises, river dolphin and several kinds of whalebone whale. Seal and sea cow bones also are found. Most of the whale and many of the porpoise skeletons are of immature animals, which suggests that this area was a calving ground.

Porpoise and whale vertebrae are fairly common. Ear bones wash up occasionally but porpoise teeth are scarce, considering the abundance of skulls and that the jaws of some long-beaked porpoises contained over 300 teeth.

Land Mammals. Remains of land mammals occasionally erode out. The deposits were marine so most of the shells and bones in the cliffs are those of animals that lived in the sea. Bodies of land mammals floated down rivers from time to time, however, and became buried in the sea floor. Peccary teeth and bones, although quite unusual, turn up more often than those of other land mammals. Four species are known from the cliffs. In addition to the peccaries, mastodon, deer, tapir, rhinoceros, camel and horse have been reported, as have wolf, bear, dog, and cat. Some of these Miocene species, all now extinct, are known from the cliffs by a single tooth or two. The mastodon teeth represent the first known appearance of mastodon in North America.

Birds. Most of the fossil birds found in the vicinity of Scientists' Cliffs were pelagic, spending much of their lives at sea. Bones of gannet, auk, loon, shearwater, jaeger, and tropicbird have been reported. Recently, wing bones, vertebrae, ribs and the beak of an extremely large pelican-like birth that stood about six feet tall and had a wingspread of 15 to 20 feet have shown up. A one-half size scale model of this bird, named Pelagornis but better known as the false-toothed bird, is displayed in the paleontology exhibit of the Calvert Marine Museum in Solomons Island.

Sharks, Rays, and Bony Fish. Shark teeth are the favorite fossils of local beachcombers. They vary in size from barely visible to teeth of the great white shark measuring five inches or more. There are so many that you can almost always find a few by the water's edge.

Teeth commonly found on our beach include sand shark, mako shark, silky shark, snaggletooth shark and white shark. The shark in the story "Jaws" was a white shark but less than half the size of the Miocene monsters with five inch teeth, which are estimated to have reached more than 40 feet in length. Shark teeth are found throughout the deposits.

Many kinds of fish in the Bay today frequented the area millions of years ago. Bluefish, weakfish, ocean catfish, sturgeon and black drum were present, as were cod, sailfish, ocean sunfish and other types. Fish remains are plentiful but usually consist of isolated vertebrae, scales and an occasional tooth

Reptiles. Crocodiles, fresh and saltwater turtles, and a land dwelling tortoise have been reported from the cliffs. Crocodile teeth show up fairly often but complete skulls and other parts of the skeleton are rarely found. Fragments of sea turtle shell are among the most common vertebrate fossils in the Calvert Formation.

Mollusks. The Calvert Cliffs are notable for their densely packed beds of mollusk shells - clams, oysters, scallops, and snails among others. Our local shell beds can be seen from all along the beach, with the best view that from about halfway between South Beach and Governor Run.

Mollusks (and diatoms and foraminifera) are especially useful in determining the age of a formation. Geologists use the percentage of fossil species that have survived until today as one measure of age. As shells usually are numerous, percentage distributions of the various species can be correlated with those from other deposits. Some 400 species of mollusk have been identified from the cliffs, of which about 11 percent are still living.

One of the first illustrations of a fossil from America, a snail now called Ecphora gardnerae, was published in a 1770 edition of one of Martin Lister's works. This shell may have been collected by Hugh Jones, rector of Christ Church in Port Republic from 1696 to 1701. An active naturalist, he collected and sent back to England many local plants, animals, and fossils. In 1984 the Maryland State Legislature designated this graceful shell the official State fossil.

Miscellaneous Fauna and Flora. Other fossils found on the beach include sea urchins, sand dollars, crab claws, barnacles, coral and a brachiopod. Sea urchins were considered rather rare until 1938, when a pocket containing hundreds of individuals was found at Scientists' Cliffs in a sandy bed near the base of the Choptank Formation. Paleontologists of the U.S. National Museum placed a large block from this pocket on exhibit there, and another in the Chestnut Cabin Museum where it remains our prime exhibit. Similar colonies at the same level are exposed infrequently. Clean, well preserved sand dollars are found with these sea urchins but not in such profusion. Sand dollars also appear in other beds but these usually are broken and encrusted with barnacles and mollusks.

Carbonized wood is plentiful in the Chesapeake Miocene. Most of the wood in the Scientists' Cliffs area is believed to be cypress. However, investigations of these deposits here and near Washington and Richmond have yielded leaves and pollen of several other species including oak, hickory, pine, elm, and basswood.



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