Dr. Ken Lacovara isn’t sure about that yet, but he’s working to figure it out. Lacovara, an associate professor in the College of Arts and Sciences at Drexel, has been digging at this particular greensand mine for years. A long line of famous paleontologists dug at this site before him. And, in fact, New Jersey has a history of significant paleontological finds: The world’s first dinosaur skeleton was found nearby in Haddonfield, New Jersey. (That specimen now belongs to the Academy of Natural Sciences of Drexel University.)
But, until recently, Lacovara appreciated his New Jersey dig site primarily for its location and not its legacy. Less than a 30-minute drive from Drexel’s campus in Philadelphia, it’s a convenient place to bring students to get hands-on field experience with paleontology. (He runs what he calls a “no-room schoolhouse” with more experienced students training new students and volunteers, in the open-air setting.) The dig site is highly productive, with dozens, if not hundreds, of fossils of marine reptiles, fish, and invertebrates turning up every season. But Lacovara always made his most exciting finds — supermassive sauropod dinosaurs– in far-off places like China, Egypt, and Patagonia.
He’s a lot more excited about New Jersey, lately. Because this dig just might be a place where you can dig in the dirt, pick up a fossil and say, “This creature died when the dinosaurs did.” This pit’s fossils might be from that very bad day. This might be the only place on Earth where you can say that.
When Lacovara talks about this idea, he’s careful to point out that it’s just a hypothesis right now: an idea that he and his students will put to the test through careful collection of evidence.
As he mentions in that story, Lacovara has a few lines of evidence suggesting that the fossils he’s finding may have come from the big Cretaceous extinction day.
- The fossil layer containing the bone bed comes from somewhere (geologically speaking) very close to that time, in the late Cretaceous. And none of the Cretaceous vertebrate fossils are found above the bone bed. By itself, that’s not conclusive; it just tells us that no living vertebrates from even later in the Cretaceous happened to die and become fossilized above them. But there’s more.
- The immense bone bed contains a lot of articulated vertebrate skeletons – complete turtle shells, an entire crocodile, and more, all still connected to one another. Lacovara recently explained to me that there are three scenarios in fossilization that lead to bone beds. Only the scenario he called “Everybody dies at the same time” would typically leave behind articulated skeletons. (The other two scenarios, slow accumulation of fossils in a sedimentary area, and a wash-away deposit, tend to result in weathering and sinking of the fossils, he said.)
The pieces that haven’t fully come together yet for Lacovara’s hypothesis are the evidence of the asteroid impact. If a massive asteroid hitting the earth caused the deaths of these animals in the bone bed (as well as a mass extinction event across the entire planet), there may be chemical and physical signs of it. So far, he said, they have some such evidence, but not enough yet to say definitively whether the New Jersey fossils did or didn’t die on extinction day. This evidence would include chemicals rarely found on Earth such as iridium; ash layers from the global forest fires; and tiny pebbles of glass known as tektites, formed from molten rock that cooled as it fell from the sky; and a few other factors.
The digging continues.