At first glance, turtles and tortoises seem almost interchangeable. Both carry a shell, move at an unhurried pace and belong to the same ancient reptile lineage that has existed for millions of years.

It would be a memorable sight. But it would also be so wrong to tip over Galápagos giant tortoises to see how shell shape affects their efforts to leg-pump, neck-stretch and rock right-side up again.