Cracking open the fossil record

Jasmina Wiemann wanted to be a paleontologist before she could even pronounce the word. "I was a weird kid," she says. Growing up in the countryside outside of Bonn, Germany, she collected tokens of the natural world: flowers, rocks, and insects. But it was in a bookstore, at age 3, where Wiemann says her scientific journey truly began.

"I got obsessed with the cover of this book about past life—not just dinosaurs but saber-toothed cats and trilobites—animals so alien from what we have around today," she remembers. "It just made me incredibly excited."

As it turns out, a number of fields would excite Wiemann, who went on to earn degrees in geology, chemistry, and evolutionary biology. In 2018, when she arrived at Yale for her PhD, she wanted to get back to her first love, paleontology, without abandoning everything she had learned along the way. She decided to "blend all those things together" and devote herself to the nascent field of molecular paleo­biology, the study of ancient biomolecules recovered from fossils.

Over the past decade, Wiemann discovered new methods for wringing more information from these fossils than scientists previously believed was possible. "We used to think fossils were dead rocks," she says, "but that's absolutely not true."

By finding and analyzing soft tissue preserved in dinosaur fossils, Wiemann has fundamentally revised our understanding of the extinct behemoths, from their parenting styles to the squishiness of their eggs to the speed of their metabolisms.

This fall, Wiemann joined the faculty of Hopkins to launch her PaLEO Lab in the Department of Earth and Planetary Sciences, where graduate and undergraduate students will, among other pursuits, examine what past extinctions can tell us about how life will evolve in the face of global climate change.

Wiemann was an undergraduate herself when she made her first consequential discovery. She needed to nail down a topic for her senior thesis at the University of Bonn just as her adviser was heading out on sabbatical. "You can do whatever you want," he told her, depositing a bag of fossils on her desk. "But we have these leftover fossil eggshells, and if you can get anything out of them, that would be amazing."

Wiemann tried to imagine the most interesting question she could answer about dinosaur eggshells, and her mind soon turned to color. A long-held assumption was that dinosaur eggs were pure white like alligator eggs. What if that wasn't true?

"We'd always assumed that egg color is an avian innovation," she explains. "Blue jays lay greenish-blue eggs; American robins lay bright blue eggs." But scientists have been wrong about bird evolution in the past, once believing that most avian features had evolved in service of flight or unique habitats.

"Lots of these traits actually evolved in their dinosaur ancestors," Wiemann says. For example, dinosaurs relied on feathers for thermal insulation long before birds used them to fly. She wanted to know: Could egg color have originated with dinosaurs?

There are two molecules that give rise to all the diversity in egg color in modern birds. To search for those color pigments, Wiemann dissolved bits of the 67-million-year-old shells in a solution that removed the calcium and allowed her to search through the samples' chemical composition. She found what she was looking for—that pair of molecules. Wiemann's work proved that the eggs in the nest of a velociraptor, instead of being white like alligator eggs, looked a lot like the vivid blue ones we find scattered on the sidewalk every spring.

The discovery not only changed what scientists thought they knew about dinosaur eggs; it changed their perception of the creatures themselves. "We tend to think of dinosaurs as cold-blooded reptilian monsters," Wiemann says, much like today's scaly creatures that mostly abandon their eggs after laying them. "But egg color in modern birds is directly linked to different kinds of parenting strategies, so this diversity of parental behaviors was probably present in dinosaurs. Velociraptors, oviraptors, all the raptors that Jurassic Park painted in such a bad light, they were actually very loving parents."

The 2018 study was published in the journal Nature, earning Wiemann mentions in the pages of Science, National Geographic, and The New York Times. But for her, the work felt unfinished. There was something about the experiment that nagged at her.

"When I extracted the pigments from these shells, at the bottom of the reaction flask there would be this unspectacular brown precipitate," she says. Just what was this brown sludge? Once at Yale, Wiemann decided to find out.

Under the microscope, it looked a whole lot like soft-tissue structures: cells, blood vessels, and nerve projections. But the idea that soft tissue could persist for hundreds of millions of years flew in the face of paleontological wisdom. "We thought that biological material disappears or turns into rock," Wiemann says, "and that none of that information could ever be recovered."

Undeterred, she turned to Raman spectroscopy, a technique that would tell her exactly what she was seeing by using a laser to separate out the chemical components of the sample.

The spectrometer revealed that the brown sludge was, in fact, quite spectacular. In short, it was the residue of cellular protein, which had once lived inside the soft tissue of the dinosaur. When the animal died, it reacted with sugars and lipids to form a resilient polymer, impervious to heat, water, and decay. (You've no doubt seen this same reaction, which occurs when your oven transforms the protein in your bread into a toasty brown crust.) Different proteins transform into different polymers, allowing scientists to glean a remarkable amount of information from the soft tissue preserved in fossils that were, until recently, dismissed as dead rocks.

While these polymers no longer contain DNA, scientists can use Wiemann's method to learn about the physiology and metabolism of long-extinct animals and about their phylogenetic relationship to one another. So far, Wiemann has employed it to determine that most dinosaurs were warm-blooded and that the eggs they laid were soft.

Now Wiemann is turning her attention—and her spectrometer—to one of the most pressing questions of our time: How will life respond to climate change?

"We're living in the sixth extinction right now," she says, referring to human actions wiping out species at an alarming rate. "While we can model quite accurately how biodiversity will respond in the short term, we have absolutely no idea what will happen in the longer term."

For insight, Wiemann says, we can look to what she calls the "the longest experiment on physiologic response to climate change": the history of life.

What physiological features gave some species an advantage? What features may have driven others to extinction? How did past life evolve in the wake of rising temperatures and sea levels? To answer these questions, she plans to equip the PaLEO lab with a "very fancy" Raman spectrometer with three lasers capable of providing cellular to subcellular resolution. "It's going to be one of the best setups in the world," the scientist says, "where we can ask big, paradigm-changing questions."