Fossils are mysterious objects: tantalisingly like modern shells or bones in shape and substance but dug from the ground, stony and lifeless. It is hardly surprising that the explanation of their origin - as the remains of once-living organisms - achieved universal acceptance only in the 18th century. But how were fossils interpreted before then?
To find out, we need to consider not only the writings of early naturalists such as Pliny the Elder (AD23-79), but also archaeology and folklore. In a previous book on the subject, The First Fossil Hunters: Paleontology in Greek and Roman Times (2000), focusing on the bones and teeth of vertebrates, Adrienne Mayor described how bones of the dinosaur Protoceratops may have seeded the myth of the griffin, and fossil skulls of pygmy elephants the legend of the Cyclops. Here, Kenneth McNamara turns our attention to smaller fossils - those of sea urchins, one of the commonest fossil invertebrates.
Sea urchins are related to starfishes, sharing with them bodies with a distinctive fivefold symmetry. Unlike starfishes, however, sea urchins have robust skeletons of calcium carbonate that are able to survive after the animal's death and become fossilised. A major source of fossil sea urchins both today and in prehistoric times has been the Chalk, a pure white limestone of Cretaceous age carpeting large areas of northern Europe. The infilling and envelopment of Chalk sea urchins by flint, the best material for making stone tools, ensured that these fossils did not go unnoticed. For example, an early Palaeolithic flint hand-axe excavated at Swanscombe in Kent was carefully sharpened on one side only so that a fossil sea urchin was left undamaged.
Compelling evidence that our ancestors treasured fossil sea urchins is provided by the inclusion of these fossils in graves dating from the Palaeolithic era until at least the 12th century AD. The most celebrated is a Bronze Age burial on Dunstable Downs excavated by Worthington G. Smith in 1887. The grave contained the skeletons of two individuals, a female nicknamed Maud and her infant, surrounded by more than 200 fossil sea urchins. The considerable effort involved in collecting so many fossils and placing them neatly around the two bodies is testament to the value accorded to these "star-crossed stones". More difficult to comprehend, however, is the exact significance of the fossils to these people, although the five-rayed markings on the surfaces of the fossils invite comparison with the stars and hence various celestial beliefs.
Further clues about the significance of fossil sea urchins can be found in folklore. In parts of rural England and Denmark they are referred to as "shepherds' crowns" and "thunderstones". One belief is that good luck will come to finders of a shepherd's crown if they spit on it and throw it over their left shoulder. Thunderstones were supposed by some to fall to ground during thunderstorms as gifts of the god Thor, with those in possession of a thunderstone gaining protection from future lightning strikes.
McNamara, a lecturer in palaeontology at the University of Cambridge, skilfully mingles anecdote with hard evidence to explore the symbolic significance of fossil sea urchins. The result is a scholarly but highly accessible book, peppered with stories of the archaeologists responsible for excavating sites containing fossils, including the illustrious Augustus Pitt-Rivers (18-1900).
The author's account of his own boyhood experiences as a fossil collector roaming the South Downs in search of sea urchins serves to illustrate how fossil collectors since the beginning of humankind have been motivated not only by the desire to possess these tactile, attractive and symbolic fossils, but also the thrill of the hunt. Notwithstanding the unnecessary inclusion of several fictional vignettes, there is much in The Star-Crossed Stone to inform, stimulate and entertain.
The Star-Crossed Stone: The Secret Life, Myths, and History of a Fascinating Fossil
By Kenneth J. McNamara
University of Chicago Press 256pp, £18.00
Published 30 November 2010