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The Head of a Shark“He made us see everything there is to see in the construction of the eye,” a French physician wrote, “without putting the eye, the scissors, or his one other small instrument anywhere but in his one hand, which he kept constantly exposed to the gathered company.” The eye in question was that of a horse. The young man, of course, was Steno. With no suitable position available in Denmark, Steno had traveled through Germany for several months, then moved to the bustling multicultural city of Amsterdam, where he stayed with a physician named Gerard Blaes. While visiting Blaes, Steno casually undertook the dissection of a sheep’s head, and accidentally discovered the parotid gland, which produces saliva. Blaes initially dismissed his guest’s find, but after the young man attracted the attention of others, Blaes claimed the discovery as his own. The dispute turned ugly, and soured Steno’s interest in taking credit for his discoveries, though that didn’t keep him from making new ones. In 1662, he published “Anatomical Observations on Glands” describing all the glands in the head. In Paris a few years later, he delved into studying muscles, realizing that they worked through contractions of muscle fibers, not—as was commonly believed—through ballooning. He went on to make key finds about the anatomy of the brain. He moved on to Florence, and quickly found life under the Tuscan sun smelly. Francesco Redi, the man Steno hoped to meet, was busy conducting experiments in spontaneous generation. It was common knowledge that decay gave rise to new life, namely flies and worms. The influential German Jesuit Athanasius Kircher was so convinced of this that he even published recipes. Redi had his doubts, and to prove them, he assembled rotting meat, animal carcasses, and ox dung. He found that when he carefully covered the decaying lumps, no lowly new animals appeared. Steno felt strangely at home in this environment, and the powerful Medici brothers, the grand duke Ferdinando and his brother Leopoldo, soon took an interest in him. When they acquired the head of a great white shark in October 1666, they delivered it to Steno for dissection. Steno found that the shark’s upper and lower jaws each held 13 rows of teeth, and the teeth resembled glossopetrae, or tongue stones. 
Steno published his description of shark teeth shortly after dissecting a shark head. (Image from The Seashell on the Mountaintop by Alan Cutler) Tongue stones turned up everywhere, yet no one knew just how they originated. Some people thought they fell from the sky, maybe on moonless nights when no one could actually see them falling. Many people associated them with a story about Saint Paul, that while he was shipwrecked on Malta, he had either turned serpents to stone or at least deprived them of their venom. Yet tongue stones looked like neither the tongues nor the fangs of snakes. What they did look like, Steno found, were shark teeth. Steno wasn’t the first to correctly identify shark teeth, and he didn’t even state with certainty what they were, but his published illustrations left little doubt. Sharks regularly shed teeth and grow new ones throughout their lives, so their teeth are not difficult to find. Extinct sharks have left their teeth inside ancient rocks just as modern sharks have strewn teeth across modern beaches. Steno had found the origin of a common vertebrate fossil, but that didn’t mean all such mysteries were solved. next: The Nature of Fossils
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