Fossil Whale Offers Clues on Feeding, Handedness
News Article: Hamptonroads.com
By Diane Tennant
© August 19, 2009
From a patch of ancient seafloor that lies west of Interstate 95, a fossil whale with a broken jaw presents a mystery that may have been solved with today's publication of a paper by the Virginia Museum of Natural History.
The partial skeleton came from a quarry north of Richmond that is considered the best fossil site in Virginia.
"It's just incredibly rich," said Alton C. Dooley Jr., a paleontologist at the museum and co-author on the paper. "I can dig here for the rest of my life and we won't get it all done."
At least a dozen whales have been found at the dig, which is in a quarry operated by Martin Marietta Aggregates. The first whale found was a new species, and a cast of the skeleton is the centerpiece of the nearby Caroline County visitor's center. After that came one rare find after another - whales piled on top of each other, dolphins and sea turtles alongside pieces of land animals such as a horse, a camel, a tapir and a peccary.
Based on the shells of microscopic algae called diatoms, the water at this site was no more than 50 feet deep and probably brackish rather than salty, Dooley said. Several thousand shark and ray teeth have been collected; there are so many that erosion litters them across the surface of the ground.
"We've actually only excavated about 5 percent of this site," Dooley said.
Digging began on a small scale in 1991. As scientists came to realize how unusual the site is, the pace of digging picked up, but it will take years to complete.
About 50 species have been identified so far, and the museum has in storage about 60 plaster "jackets" containing large chunks of rock and earth holding fossils that have not even been opened, let alone cleaned and identified.
For two years, Dooley and his team have been excavating the longest and most complete whale skeleton ever found at Carmel Church. It is the first whale found there with at least part of its tail in position. For two weeks in August, volunteers, including Kayla Leyden, a rising senior at Lakeland High School in Suffolk, painstakingly dug around it with paintbrushes and dental picks.
Scientists do not know why so many whales and other animals are in such a small space - the fossil beds run in a narrow band for about 400 feet. The bones of different species are intermingled. Some lie neatly in place as though the animal died and was buried quickly by sediment, but the bones of other whales are scattered and bear bite marks from scavenging prehistoric sharks.
The 14 million-year-old whale featured in the scientific paper was found in 2006. It lay upside down, tail and flippers missing, and its position obscured the most interesting thing about it: the broken left jaw.
Broken bones are not unusual in a fossil bed. But this whale's jaw had new bone growing around the broken ends, showing that the animal had lived for at least a week after the injury. In addition, the left side of the snout had been crushed, and the left jaw joint damaged.
Such an injury has never been reported in a fossil baleen whale, Dooley said. In modern whales, broken jaws are usually caused by ships hitting them.
"But ship collisions were certainly not occurring in the Miocene, so what sort of event could lead to a fracture?" Dooley and co-author Brian L. Beatty ask in the paper.
A clue was provided by the ribs. Most marine mammals have lightweight spongy bones to help them float. The fossil ribs were heavy and denser than expected, more like the bones of modern-day sea cows that act as ballast to hold them down as they feed on submerged plants.
It had always been assumed that most baleen whales, fossil and modern, were filter feeders, Dooley said, straining mouthfuls of seawater through tough, stringy plates of baleen that take the place of teeth.
But Pacific gray whales are bottom feeders, using their baleen to filter sediment for food. They usually turn to the right as they gouge holes in the seafloor; only about 20 percent of gray whales prefer the left side.
Based on the injury and the dense bones of the fossil, Dooley and his co-author from the New York College of Osteopathic Medicine concluded that the fossil whale was also a bottom feeder, and may have injured its jaw by hitting something on the seafloor.
"This is the first time we've got solid evidence for feeding from the seafloor in a baleen whale," Dooley said. "This is also the first time handed behavior is described in a fossil whale. We were just lucky we got a left-handed one."
Mark Uhen, a term assistant professor at George Mason University who is not involved with the paper, said it is difficult to find fossil evidence of behavior.
"This is rather special, that he's hypothesizing evidence of feeding behavior just from the bones," Uhen said. "Evidence of it in a fossil is pretty neat."
Nick Pyenson, soon-to-be curator of fossil marine mammals at the Smithsonian, said the interpretation is hard for other scientists to replicate.
"I guess I'm very skeptical of any claim of behavior," he said. "It's difficult to test."
Dooley hopes to examine more mysteries at Carmel Church, such as why so many apparently healthy adult animals ended up there, their bones intermingling. Some evidence suggests it happened relatively quickly; other evidence points to a longer time frame.
He also expects to find new animals as more of the quarry fossil beds are exposed. He's hoping for a relative of the saber-toothed cat, or a prehistoric rhino, more horses or a seal. The teeth of a four-tusked elephant called a gomphothere were found some years ago in Westmoreland County, in the same soil layer that Dooley is working on at Carmel Church.
"I feel like a gomphothere is in there," he said. "I can hear it calling to me."
Diane Tennant, (757) 446-2478, firstname.lastname@example.org