Zoologists believe that chelonians have a more advanced protective structure than is found in any higher vertebrate, which has allowed them to survive threats of all kinds. In fact, up to the present, their exteriors haven't changed to any remarkable degree. Turtles and tortoises have displayed remarkably slow evolution.
雖然動物學者認為，烏龜的安全構造，比任何高等脊椎動物都進步，可以度過各種外來環境壓力，因此烏龜出現至今，外型並未作太大改變，是演化極慢的物種。