The process of fossilization is not kind to the brain. Nor indeed to any soft tissues, the anatomy of which are usually not preserved in the fossil record. How then to go about examining and unravelling the evolutionary history of the vertebrate brain? Nowadays we might first think to tackle this problem using 3D imaging techniques to virtually reconstruct the endocast of a fossil to capture the external features of the brain that have been imprinted on the internal surface of the cranium. But how accurately does a fossil brain endocast reflect the anatomy of the unpreserved tissue, and to what extent can features of an endocast be used to make palaeobiological inferences about its extinct owner? Answers to these and other questions are possible through the pioneering work of the German palaeontologist Tilly Edinger (1897-1967), who founded modern paleoneurology (the study of fossil brains) in the 1920s, tackling for the first time issues that still form the basis of research today.

tilly edinger

Much like wax pouring into a mold, sediment can fill fossil crania and become cemented hard over time, preserving the internal features in what is known as a natural endocast. Such specimens are rare, and Edinger’s interest in fossil brains was first sparked by the study of a natural endocast of the Mesozoic marine reptile Nothosaurus as part of her doctoral dissertation at Frankfurt University. Following her graduation in 1921, Edinger later published a description of the endocranial cast of Nothosaurus [1] in what was to be her first research paper. Importantly, she realized that despite a large literature on such fossil specimens, these were mainly considered curiosities and had not been examined in a comparative or geological (temporal) context. She endeavored to collate and synthesize this information into a book (Die fossilen Gehirne, Edinger 1929), it defined a new field and detailed the questions that Edinger set about to answer over the course of her research career [2].

It was, however, far from plain sailing. Although Edinger could continue her research, having secured several unpaid research assistant positions following her graduation, by 1933 her position as curator of fossil vertebrates at the Senckenburg Museum of Natural History in Frankfurt had become increasingly difficult under the restrictive racial laws of the Nazi regime. By 1938, after Kristallnacht, she was unable to return to work and forced to flee.

Following a short spell in London, Edinger landed on American shores in 1940 and took up her first salaried position, at Harvard’s Museum of Comparative Zoology. Within months of her arrival she went on to attend the founding meeting of the Society of Vertebrate Paleontology, at which she was the only woman present [3]. Later she would go on to be the first female president of the society (1963).

During the next years at Harvard, Edinger continued to publish highly detailed, thorough anatomical works. Among the most famous of those was a monograph, ‘Evolution of the Horse Brain’ [4], spurred by a meeting with George Gaylord Simpson. Edinger described a series of horse brains, showing differences in size and external anatomy, using a framework of stratigraphic sequence to reconstruct the pattern of evolutionary change in geological time. She concluded that many features of the brain must have arisen independently and in parallel in different mammalian lineages. Her work illustrated the value of the fossil record in understanding brain evolution, identifying features and trends that would not have been possible by consultation of extant material alone. The importance of paleoneurology was clear, and Edinger was to rewrite her 1929 book in English [5], a task that took many years and many museum trips around the US and Europe, where she was able to re-connect with colleagues, spread her ideas on the fossil brain and challenge earlier theoretical frameworks of brain evolution. Until her death in 1967, Edinger dedicated her time to producing the volume, and its contents remain the essential first step for any researcher embarking on work in the field of paleoneurology today.

Though she had started to lose her hearing as a teenager, and reported that she was entirely deaf without hearing aids, Tilly made her amazing contribution with her brain for rocks (and rocky brains)!

Tilly’s eventually became President of the Society of Vertebrate Paleontology, and her achievements were eventually recognised by many organisations including the Guggenheim Foundation and the American Association of University Women, while her work ensured an enduring legacy.

References

[1] Edinger T. 1921. über Nothosaurus. Ein Steinkern der Schädelhöhle. Senckenbergiana 3: 121-129

[2] Edinger T. 1929. Die fossilen Gehirne. Ergebnisse der Anatomie under Entwicklungsgeschichte 28: 1-249

[3] Buchholtz E., Seyfarth E.-A. 1999. The gospel of the fossil brain: Tilly Edinger and the science of paleoneurology. Brain Research Bulletin 48(4): 351-361

[4] Edinger T. 1948. Evolution of the horse brain. Geological Society of America Memoir 25: 1-177

[5] Edinger T. 1975. Paleoneurology 1804-1966. An annotated bibliography. Advances in Anatomy, Embryology, and Cell Biology 49: 1-258

Post submitted by Laura Wilson

Edited by Brenna

Image Permissions granted from the Archives of the Museum of Comparative Zoology, Ernst Mayr Library, Harvard University. The portrait is dated 1948. Published in Tilly Edinger: Leben und Werk einer jüdischen Wissenschaftlerin by Rolf Kohring & Gerald Kreft, Stuttgart 2003.

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