How a fascination with fossils unearthed new neurology.
Have you heard of neurology, the study of brains? What about paleontology, the study of fossils? Did you know that you can combine them into one discipline? If you are interested in brains and fossils, then you should hear about paleoneurology. Dr. Johanna Gabrielle Ottelie Edinger, or Tilly Edinger, was the pioneer of this field– one of the most influential paleontologists of the 20th century. But her academic success in paleontology was unusual. Not only was she a woman in academia in a time when very few women were, but she also was Deaf. What’s more, Dr. Edinger was Jewish, and her life and research were upended by living in Germany during the Holocaust. While the world seemed against her, she persevered, founding the field of paleoneurology and discovering secrets of long-dead organisms.
Watch the video or continue reading the blog version below!
Clues From the Past
Paleontologists study the history of the Earth through fossils. Fossils are rocks that contain remnants of living organisms from long ago, and there are many ways they could form. Fossilized remnants can be things like bones, shells, hardened footprints in mud, or the imprints of living material that has since decayed away (such as plants or animal tissue). Paleontologists use fossils to study what types of plants, animals, bacteria, insects, and fungi lived on Earth at various stages of the Earth’s history. They can also learn about how the climate, ecosystem, and geology of a region has changed over time.
But there’s a big problem with learning about these extinct organisms from fossils: it’s very rare for soft tissues to be fossilized. Soft tissues include things like muscles, skin, and organs, which decay much faster than bones, teeth, or shells. This can make it super difficult to learn about ancient animals’ bodies. Paleontologists have to come up with clever ways to get information from the fossilized clues they dig up, and Tilly was as clever as they come!
Fascinated by Fossils
Tilly was born in 1897 in Germany. She began to lose her hearing as a teenager due to a disease called Otosclerosis. She was fascinated by the brain from an early age since her father was a neurologist, and this passion led her to earn her PhD from the University of Frankfurt in paleontology, geology, and zoology.
During many years of the Holocaust, Dr. Edinger had to carry out her research by sneaking into her work building and hiding her hearing disability. She even had her name tag removed from her office to avoid drawing attention to herself. She tried to move to America, but was initially denied because of strict immigration quotas. In 1940, she was approved to bypass the quotas and move to America because she was hired as a research associate at Harvard University. She was one of only
four female scientists who were granted this kind of aid.
Dr. Edinger became a US citizen in 1945 and came to think of Boston as her home.
Mystery of the Missing Brains
As a paleontologist, Tilly was fascinated by the soft tissue of ancient organisms, the kind of tissue that isn’t fossilized and is lost to time. But Dr. Edinger realized that although the brain decays, it can leave an imprint in the skull that can tell us how its surface was shaped.
She came up with the idea of using these fossilized skulls as molds. By covering the inside of the skull with rubber or plaster, you get a replica model of the organism’s brain. These internal casts of a hollow object are called endocasts. Tilly had made a huge discovery: endocasts could be used to reconstruct parts of the neural anatomy of ancient animals, allowing paleontologists to study their brains almost like they would study any other brain.
Tilly used this method to learn about a dinosaur called the Nothosaurus, which was a marine reptile from the Mesozoic era. The Mesozoic era was between 66 million and 252 million years ago, so the information that their fossils hold can be very important to learn what life
was like for creatures in the Triassic, Jurassic, and Cretaceous Periods. As part of her research, Tilly studied a natural brain cast made of fossilized mud that had been discovered inside a skull. This inspired her to start making endocast molds and found the entire field of paleoneurology.
While Dr. Edinger worked at the Harvard Museum of Comparative Zoology, she researched the evolution of another organism - horses. By studying the endocasts of their brains across a single geological time era, she tracked the subtle changes in size and surface folds that progressed over thousands of years. Since evolution happens over such long periods of time, this kind of study would be impossible to conduct on preserved brain samples, simply because brain samples haven’t been collected and preserved for a long enough time. Dr. Edinger’s use of fossil samples and endocasts uncovered entirely new knowledge about neurology and the evolution of mammals.
Below are a few examples of the endocasts made by Dr. Edinger during her career. The left picture is from a porpoise, the middle picture is of a horse skull, and the right picture is from an otter.
Brains are really complex with lots of internal structure, but we know different regions of the brain process different things. For example, the sense of smell comes from a section called the olfactory lobes, and for whales this region sits on the outer layer of the brain. Tilly studied the skulls of whales throughout history and found that the indents made by the olfactory lobes got smaller over time, indicating that their sense of smell was reduced. This evolution makes a ton of sense, since whales are mammals and it’s pretty hard to smell underwater when you only breathe air!
Casting a New Field
Dr. Tilly Edinger founded an entirely new field. Paleoneurolgy was born from her unique passions in multiple subjects. Throughout her career, she followed those passions, found new questions to explore, and mentored many students in this budding new field. She even has a bone named after her– the Tilly bone!
Dr. Edinger thought creatively and found a way to do what seemed impossible: study the brains of long-gone animals. Countless secrets of the ancient world were unlocked through Tilly’s dedication to bones and the stories they tell.
Photos of endocasts courtesy of the Museum of Comparative Zoology, Harvard University
Photos of Dr. Edinger and Nothosauraus Skull from the Ernst Mayr Library and Archives of the Museum of Comparative Zoology, Harvard University
Written by Lauren Bell
Edited by Madelyn Leembruggen
Illustrations by Taylor Contreras
Portrait by Jovana Andrejevic
Sources and additional readings:
Tilly Edinger from the Museum of the Earth
Tilly Edinger from the Museum of Comparative Zoology
Legends of Rock: Tilly Edinger by Anna Ayvazyan from The Palaeontological Association
The Woman Who Shaped the Study of Fossil Brains by Leila McNeill from the Smithsonian Magazine
Fossil from National Geographic
The Study of “Fossil Brains”: Tilly Edinger (1897–1967) and the Beginnings of Paleoneurology by Emily A. Buchholtz and Ernst-August Seyfarth from Biology in History
Dig deeper into the fossils and brains
Explore (10-15 minutes): What do the different regions of the human brain that are responsible for different functions look like? Let’s explore!
Discover (5-10 minutes): Let's think like a paleonurologist and compare skulls from different era!
Make (20-25 minutes): Have you ever thought about how fossil prints are made? Let's make a 3D model of the inside of a hollow object by using a dough mix!