Nicolas Steno and the Origin of Fossils

In October 1666 a large shark was captured by a French fishing boat in the sea of Livorno (today Italy, at the time County of Tuscany), pulled onto the shore, the animal was beaten to death and dismembered, as the body was quite too heavy to be transported and only the head was saved. In Florence the Danish anatomist and naturalist Niels Stensen or latinized Nicolas Steno (born January 11, 1638) was asked to dissect this head. 

Stensen observed various anatomical particularities: the skin was covered by glands, secreting a reddish slime. Steno assumed that this slime would keep the skin smooth, helping the animal to move in water (today the ampullae of Lorenzini are considered part of an organ to sense electromagnetic fields). He noted also the structure of the brain, arguing that it appeared quite too small to coordinate such a large animal, so also the spine must have some role in (unconscious) movements (like reflexes). Finally Steno studied the mouth, noting the ranks of sharp teeth.
 

Steno, after the anatomical description, adds a chapter comparing these teeth with common fossils - the Glossopetrae or tongue stones. It´s important to note that Steno was not the first to speculate over the organic origin of such fossils, already in 1616 the Italian Fabio Colonna (1567-1640) explained glossopetrae as shark teeth. However many naturalist argued that the organic origin of fossils could not explain how such remains of sea animals  could become entrapped in rocks, found on dry land and even high in the mountains. 

Fig.1. Recent, mummified shark head.
 

But Steno was for the first time able to explain why these fossilized teeth were found inside rocks, far distant to the modern sea.  Steno had already observed fossils hosted in the Royal Danish Kunstkammer (Copenhagen) and in a private note he writes "Snails, shells, oysters, fish, etc., found petrified on places far remote from the sea. Either they have remained there after an ancient flood or because the bed of the seas has slowly been changed. On the change of the surface of the earth I plan a book, etc."
 

Fig.2. Steno's figure of a dissected shark head, comparing the teeth of a modern shark to the fossil Glossopetrae, from "Elementorum myologiæ specimen, seu musculi descriptio geometrica : cui accedunt Canis Carchariæ dissectum caput, et dissectus piscis ex Canum genere" (1667).
 

He also studied outcrops of layered rocks in Tuscany, recognizing the sedimentary origin and a stratigraphic order. However only with the description of the shark head he combines all his observations in one "geo-theory":

• Fossils, resembling modern animals, are not found in recent soils of dry land. If fossils were of inorganic nature, however we should find them in every kind of soil and rocks.
• The layering was formed by sedimentary deposition, the soil where fossils are found once was therefore a sort of liquid mud, so that bodies of dying animals could become imbedded into it
• Those soils were deposited and therefore covered once by water, this explains why fossils resemble animals of the sea
• The sea can become repeatedly dry land by movements and disturbances of earth´s crust , the fossils in the mud are uplifted, the mud dries and becomes hard soil, therefore fossils can be found high in the mountains

However Steno's work, like the work of many others before him, was ignored for decades. Then a certain John Woodward, considered an amateur physician and naturalist by some, by others a quack, used/stole the principles formulated by Steno in his 1695 book "An Essay toward a Natural History of the Earth". The best part of work, thought to support the idea of the biblical sin flood as origin of the fossils, were the text passages copied from Steno.
However the book of Woodward and the principles of Steno used in it initiated a new interest in the study of sedimentary rocks.

Bibliography:

KARDEL, T. & MAQUET, P. (eds.) (2013): Nicolaus Steno - Biography and Original Papers of a 17th Century Scientist. Springer Publishing: 739