A geologist walked tortoises over pie crust. He was trying to match the first fossil footprints ever described by science. He compared the two sets of tracks, and he named the wrong animal.
In a red sandstone quarry in southern Scotland, the quarrymen kept finding footprints. The stone is bright orange, colored by a tiny trace of rusted iron. The prints turned up on the flat tops of the beds, as the stone above was cleared away. By late eighteen twenty-seven, the men had been finding them for fifteen or sixteen years. Still, no scientific work had noticed them.
One slab ended up at the home of a country minister, Henry Duncan, who also helped found savings banks. It was more than five feet long. Twenty-four footprints ran along it in two lines, twelve right and twelve left. The two lines sat six to eight inches apart. It was built into the summerhouse in his garden.
Duncan wanted to know what animal had made them. He sent casts, copies taken from the prints, to the Oxford geologist William Buckland. At first, Buckland doubted they were footprints at all. The casts changed his mind.
So Buckland tested the prints against living animals, at Oxford. First he walked a crocodile over soft pie crust. Its prints showed, he wrote, that the fossil tracks were not a crocodile's. Then he walked his own tortoises, of three different kinds, over pie crust, wet sand and soft clay.
In December eighteen twenty-seven, he wrote to Duncan. He had little or no doubt, he said, that tortoises made the fossil tracks. He admitted one gap. The prints matched none of the living kinds he had tried. Ancient tortoises, he guessed, moved faster than his own dull, torpid prisoners.
Duncan took the case to the Royal Society of Edinburgh. On the seventh of January, eighteen twenty-eight, he described the footprints and quoted Buckland's verdict. It was the first scientific report of fossil footprints. Several newspapers carried the story as footsteps before the Flood. Print came later, in eighteen thirty-one.
Twelve days later, Buckland repeated the trial for an audience. It was a party at the London home of the geologist Roderick Murchison, and the room was full of scientists. At first the tortoises would not move. Buckland flicked their tails. They had stuck fast, and each one came up with half a pound of dough on every foot.
So the guests got to work. With a rolling pin, they kneaded and rolled the dough again, sleeves tucked up, dusted in flour. At last the tortoises walked across it. One young guest, John Murray, wrote it all down four days later. Many who came to scoff, he said, went home more ready to believe.
For a while, the tortoise answer seemed to fit everything. Some prints on the slabs were long and smeared. In March, Buckland wrote that his own tortoises made marks exactly like them, on sand that was too wet.
But Duncan had already found clues in the stone itself. The quarrymen told him the tracks always ran up or down the sloping beds, never across them. On the way up, the claws had dug in deeper. The front prints were deeper than the back ones, so he guessed at a long neck or a heavy head.
He also asked whether violent gales from the southwest had piled up that sand. He was right about the sand. Inside the quarry walls, the old dune faces still show as sloping layers. The stone formed from dunes, in a dry Permian land. The animal had been climbing the steep face of a dune. Every step pushed a small crescent of sand out behind its heel.
But the animal was no tortoise. Each front print shows five claws on one rounded sole, about two inches across. A modern scan of one Scottish slab found a ridge between the tip and the base of the toe marks. That ridge is one reason experts now class these tracks with an early relative of mammals, not a reptile.
His pastry test had found a likeness, not the maker. So the first fossil footprints ever described by science were left by an early relative of mammals, climbing a dune.
The quarry stayed at work into the nineteen fifties. Late in the eighteen hundreds, its deep red stone framed the doors and windows of schools in Edinburgh. One, near the top of the Royal Mile, still shows that red trim against gray stone.
A geologist walked tortoises over pie crust, and the pastry took their prints at once. Beside them lies the trail of a very different animal, still climbing its dune in stone.
