The second coming

What Alida Bailleul saw through the microscope made no sense. She was examining thin sections of fossilised skull from a hadrosaur, duck-billed, plant-eating beast that 75m years ago roamed what is now the US state of Montana when she spotted features that made her draw a breath.

Bailleul was inspecting the fossils, from a collection at the Museum of the Rockies in Bozeman, Montana, to understand how dinosaur skulls developed. But what caught her eye should not, the textbooks said, be there. Embedded in calcified cartilage at the back of the skull were what appeared to be fossilised cells. Some contained tiny structures that resembled nuclei. In one was what looked like a clump of chromosomes, the threads that bear an organism’s DNA.

Bailleul showed the specimens to Mary Schweitzer, a professor and specialist in molecular palaeontology at North Carolina State University, who was visiting the museum. Schweitzer had done her PhD in Montana under the supervision of Jack Horner, the resident fossil hunter who inspired the Jurassic Park character Alan Grant. Schweitzer herself had become famous – and faced waves of criticism – for claiming to have found