The body type/plan of giant tortoises hasn't changed much since the Triassic period. Like some dinosaurs, ancient tortoises were plant- eaters with armored shells for protection against predators, and like dinosaurs they were quite large. There appears to be some indication of convergent evolution between dinosaurs such as pleisiousaurs and pliosaurs which had similar body shapes to pre-historic giant tortoises. However there is fossil evidence that Eunotosaurus may have been the fore runner of modern giant tortoises.
Giant tortoises may share some visual similarities with dinosaurs, including certain bodily features that ensure for better movement, better swimming, and the like, but genetically, they're separate and birds are far closer. However, there were prehistoric turtles large enough to eat crocodiles, and turtles survived the meteor impact that wiped the dinosaurs. Tortoises may not be similar to dinosaurs, but at the time of dinosaurs, there were also fearsome turtles. They evolved independently to become what we know today. They lived alongside dinosaurs even if they weren't similar.
The term dinosaur translates to "giant lizard," which indicates that dinosaurs were reptiles. While they may not have carried shells on their backs, they do have enough in common with tortoises to be considered similar. Many scientists believe that they were cold blooded. Dinosaurs produced eggs and had rough skin similar to that of a tortoise.
A team of scientists has reconstructed a detailed 'tree of life' for turtles. Next generation sequencing technologies have generated unprecedented amounts of genetic information for a thrilling new look at turtles' evolutionary history. Scientists place turtles in the newly named group 'Archelosauria' with their closest relatives: birds, crocodiles, and dinosaurs.