This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
The German naturalist F. W. H. Alexander von Humboldt (born September 14, 1769-1859) is remembered as great geographer and explorer (maybe his name is even the most common on topographic maps), but his early education focused on mining engineering (and economy, as wished by his mother) and he made some important contributions to geology, for example he coined the term geological "formation".
However despite his interests in earth sciences, his contributions to paleontology are rare and almost forgotten...
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His education made him aware of the controversy surrounding the origin of fossil shells, still considered more as curiosities than valuable stratigraphic tools. He sure knew of the discoveries of large carcasses in Siberia, of unknown animals, maybe still living there. In 1789 he had the opportunity to have a look on the first fossil pterosaur skeleton ever discovered.
During his famous expedition to America (visited from 1799 to 1804) he collected fossil bones and shells for the great French paleontologist Cuvierand eminent geologist Leopold von Buch, he even supervised paleontological excavations near Bogotá.
In 1833 the school director and amateur archaeologist F. Sickler noted some strange holes in a stone slab used for the construction of a garden house in the village of Hildburghausen (Germany). The slab was badly damaged and Sickler was not sure what this strange fossil may be. Sickler promised to the workers in the local sandstone quarries a reward if they could provide a better specimen. Finally one year later Sickler was able to publish a short account on a new recovered slab with three distinct types of footprints, maybe from some ancient amphibious animal. He "invited" the greatest geological minds of the time, including Humboldt, to study this strange fossil. The discovery was exciting, as some imprints resemble a human hand - today these ichnofossils are known as Chirotherium ("the hand-beast").
Fig.1. Morphofamily Chiroteriidae (ABEL, 1935) - track of a large Triassic archosaur and the oldest known example of this kind of ichnofossils from the Dolomites (digits show to the right).
In a note read to the Academy of Sciences of the Institute of France in the year 1835 Humboldt made public his opinion on the mysterious fossils of Hildburghausen. He considered the imprints as real fossil trackways (some geologist, like von Buch doubted at first this interpretation) and he considered the ancient trackmaker more similar to a mammal than an amphibian. Based on the toe configuration, Humboldt imagined at first a marsupial, possibly an arboreal possum-like creature. This idea was based on the imprint of - what Humboldt believed - an opposable toe visible in the Chirotherium tracks.
Despite an expert in reptilian anatomy, he had observed caimans along the shores of the Orinoco and studied a Nilecrocodile in an Italian collection, he didn´t recognize any similarities between Chirotherium and modern reptilian footprints. The identification of Chirotherium as fossil mammal tracks was at the time a scientific sensation, at it would have significantly pushed the origin of mammals into deep time (from the recent Tertiary to the Triassic).
However Humboldt´s research attracted little interest by contemporary naturalists and the opinion of British paleontologist Richard Owen, Chirotherium made by a larger reptile, prevailed. Even Humboldt in his later work "Cosmos" (published in various volumes 1845-1862) doesn´t mention his research on ichnofossils and even notes that the earliest mammals are found only in Jurassic sediments.
It´s not entirely clear why Humboldt, famous for his general interest in all earth sciences, showed so little interest in this topic. Maybe he considered his knowledge too limited, as his preliminary analysis was based only on a single specimen, to engage in a scientific discussion. Maybe he was also more interested in presenting this puzzle to the scientific community, hoping that others could solve this ancient mystery.
Bibliography:
KNOLL, F. (2009): Alexander von Humboldt and the hand-beast: A contribution to paleontology from the last universal scholar. C.R. Palevol Vol.8: 427-436