On 22nd December 2020, I gave this talk (via Zoom) to Martin Sander’s palaeontology research group at the University of Bonn, Germany. And now I am giving it to you , dear reader, the greatest Christmas present anyone could ever wish for: It’s based on a 2013 paper written with Matt Wedel, which itself goes back through many years slow gestation, originating in a discussion on a car journey in 2008.