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When people say that scientists are always changing their minds, it’s usually meant as a slight. How can anyone trust conclusions that are so prone to revision? But the fluctuating nature of science is a feature not a bug. It means that our knowledge of the world is constantly being updated in the face of new evidence.
For example, scientists from the University of Bristol recently showed that the evolutionary relationships between different dinosaurs are continuously changing in the light of new fossils. It’s a bit of an etch-a-sketch science—no sooner are family trees drawn before they’re re-drawn again. Even well-known transitions are prone to big shake-ups.
Consider the origin of birds. There is now overwhelming evidence that birds evolved from small predatory dinosaurs. Hundreds of stunning fossils illustrate the transitions from dino-fuzz to flight feathers and from grasping arms to flapping wings. The avialans (all birds, living and extinct) fit within a group of dinosaurs called the Paraves, which also includes dromaeosaurids (sickle-clawed predators like Velociraptor and Deinonychus) and troodontids (large-brained predators like Troodon).
But which of these creatures...
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