It takes a long time to make a fossil. The fossilized dinosaur bones you see in museums spent tens of millions of years buried deep underground, transformed by heat, pressure, and chemical reactions. But scientists have discovered a new way to simulate key fossilization processes in a lab in about twenty-four hours. That means that scientists will be able to build a better idea of how fossilization works and what kinds of materials, from feathers and skin to tiny molecules like proteins, can become fossils, and which ones can't.
"Paleontologists study fossils–we interpret them to learn about the evolution and biology of extinct animals. But the fossil record yields data that can be hard to interpret. For us to answer our questions, we need to understand how fossils form," says Evan Saitta, a Field Museum post-doctoral researcher and lead author of a new paper in Palaeontology. "The approach we use to simulate fossilization saves us from having to run a seventy-million-year-long experiment," explains Saitta, who worked on this project as part of his PhD at the University of Bristol under Jakob Vinther.
Scientists often learn about the fossilization process by examining naturally-occurring fossils and chemically analyzing them. Saitta and his team, however, worked backwards–they found a way to improve simulations of the fossilization process with modern-day animal and plant specimens, and then studied the materials that survived heat and pressure mimicking what real fossils undergo.
Saitta and his research partner, Tom Kaye of the Foundation for Scientific Advancement, took samples like bird feathers, lizard limbs, and leaves and used a hydraulic press to pack them into clay tablets about the diameter of a dime. They then heated the tablets in a sealed metal tube inside a laboratory oven at over 410 degrees Fahrenheit and 3500 psi pressure. After about a day, they pulled the tablets out–and the resulting specimens bore the hallmarks of real fossils made the old-fashioned way.
"We were absolutely thrilled," says Saitta. "We kept arguing over who would get to split open the tablets to reveal the specimens. They looked like real fossils–there were dark films of skin and scales, the bones became browned. Even by eye, they looked right."
The "Easy-Bake fossils" held up under a scanning electron microscope, too. "We could see exposed melanosomes, the structures that contain the biomolecule melanin that give feathers and skin their color, and scientists have found melanosomes in real fossils too. Less stable materials, like proteins and fatty tissues, don't show up in real fossils, and they weren't present in ours either," says Saitta.
"Our experimental method is like a cheat sheet," he explains. "If we use this to find out what kinds of biomolecules can withstand the pressure and heat of fossilization, then we know what to look for in real fossils."
Saitta notes that he and his team aren't the first to attempt to mimic the fossilization process in a lab, "but I think we're the first ones to get it pretty darn close." That's in part due to the new methods devised by the researchers. Previous experimental attempts to cook up fossils in sealed tubes didn't work because the unstable biomolecules that naturally break down, leak out, and disappear during fossilization stayed trapped. "When we cut them open, a rancid-smelling goo would come out," recalls Saitta. "But in our new method, with clay, the breakdown products can leak out into the sediment, so it's a more realistic and directly comparable simulation of how fossils are made. The stuff that we don't see in real fossils goes away, and the stuff that should be there stays."
Saitta's research focuses on exceptional fossils– ones that don't just include hard materials like bone, but also soft tissues like skin, feathers, and biomolecules. "There are some dinosaur fossils that are preserved not just with bones, but with a dark carbonaceous film of feathers," explains Saitta. "These fossils tell us about the evolution of birds and feathers, so it's important to understand how feathers preserve."
Saitta and his co-authors, Kaye and the University of Bristol's Jakob Vinther, are excited by the possibilities that their new experimental method unlocks. "With the ideas we have now, we could do ten years' worth of research," says Saitta. ""We're beginning to get into a gold rush–there are lots of claims of fossilized biomolecules. We're always looking for them and trying to find out what they'll tell us about life in the past."