Sharks have been swimming the oceans for about 400 million years, 200 million years before dinosaurs roamed the Earth.
Today, there are about 400-500 species of shark, “nearly all of which also existed during the Ice Age (2.6 million to 10,000 years ago),” said Jun Ebersole, paleontologist and Director of Collections at McWane Science Center in Birmingham. “Paleontologists are able to identify Ice Age sharks by comparing their teeth to those of their modern-day representatives.”
In a recently published paper, Ebersole, with colleagues Sandy Ebersole, Geologic Investigations Program director at the Geological Survey of Alabama in Tuscaloosa, and David Cicimurri, curator of Natural History at the South Carolina State Museum in Columbia, identified the first early Ice Age shark teeth (2.6 to 2 million years old) found in Alabama.
A shallow ocean covered large swaths of Alabama for most of its geologic history, making it “one of the best states in the U.S. to find fossilized shark’s teeth,” said Ebersole. “Although fossil shark teeth have been found in nearly every county in Alabama, these are the first early Ice Age shark teeth to be reported from the state in the scientific literature.”
Sharks will cycle through between 20,000-30,000 teeth in their lifetime. After the light-weight, white-colored teeth are shed, they become bluish-black to brown in color as dissolved minerals from the ocean floor replace the calcium phosphate in the teeth. Because the teeth are hard and dense, “they preserve well, making them one of the more common vertebrate fossils found around the world,” Ebersole said.
For years, Ebersole had heard about people finding fossil shark teeth on the beaches at Dauphin Island, prompting him to reach out to Robert Dixon, manager of the Estuarium at the Dauphin Island Sea Lab. Over a 25-year period, Dixon had collected nearly 100 teeth on Dauphin Island and on the nearby Sand/Pelican Island Complex.
Most of the fossil teeth found on Dauphin Island come from beach restoration efforts or strong storms that dredge material from the bottom of the Gulf of Mexico and deposit it on the island, according to the research paper.
From the recovered teeth, Ebersole and colleagues identified 12 species, including the tiger shark, bull shark, lemon shark, sand tiger shark, great white shark, an eagle ray, and a pufferfish. “Most of these species have modern representatives that still live in the Gulf of Mexico today,” said Ebersole, “but we were also able to identify two shark species that had gone extinct during the Ice Age.”
The specimens examined in the research paper are now part of the collection at the Dauphin Island Sea Lab, and will be preserved for the benefit of future research. It is the mission of the Sea Lab to pursue excellence in marine science education, research, coastal zone management policy and public engagement.
“I am sure there are many more species still to be discovered on the beaches of Dauphin Island. It is my hope that beachgoers find many more and donate them to their local museums. That way they can be studied by paleontologists and these remarkable fossils can be shared with the world,” Ebersole said.
The article, “The occurrence of early Pleistocene marine fish remains from the Gulf Coast of Mobile County, Alabama, USA,” can be viewed for free online at http://www.bioone.org/doi/full/10.18476/pale.v10.a6