Tortoise evolution: How did they become so big?

The evolution of giant tortoise might not be linked to islands, as had been previously thought. In a first-of-its-kind study, researchers present the most comprehensive family tree of extinct and extant tortoises so far. Analyzing genetic and osteological data from living species and fossil tortoise they rewrite the evolution of tortoise: Giant size evolved on multiple occasions on the mainland. https://www.sciencedaily.com/releases/2018/10/181023110534.htm