There is no single answer to this puzzle. Dinosaurs dominated the planet for around 179 million years and during that time, evolved into an enormous array of different shapes and sizes. Some were tiny, like the diminutive Albinykus, which weighed under a kilogram (2.2lbs) and was probably less than 2ft (60cm) long. Others were among the biggest animals to have ever lived on land, such as the titanosaur Patagotitan mayorum, which may have weighed up to 72 tonnes. They ran on two legs, or plodded on four. And along with these diverse body shapes, they would have produced an equally...