 The discoverer of the Galápagos Islands , Fray Tomás de <unk> , Bishop of Panama , wrote in 1535 of " such big tortoises that each could carry a man on top of himself . " Naturalist Charles Darwin remarked after his trip three centuries later in 1835 , " These animals grow to an immense size ... several so large that it required six or eight men to lift them from the ground " . The largest recorded individuals have reached weights of over 400 kg ( 880 lb ) and lengths of 1 @.@ 87 meters ( 6 @.@ 1 ft ) . Size overlap is extensive with the Aldabra giant tortoise however taken as a species , the Galápagos tortoise seems to average slightly larger , with weights in excess of 185 kg ( 408 lb ) being slightly more commonplace . Weights in the larger bodied subspecies range from 272 to 317 kg ( 600 to 699 lb ) in mature males and from 136 to 181 kg ( 300 to 399 lb ) in adult females . However , the size is variable across the islands and subspecies , those from Pinzón Island are relatively small with a maximum known weight of 76 kg ( 168 lb ) and carapace length of approximately 61 cm ( 24 in ) compared to 75 to 150 cm ( 30 to 59 in ) range in tortoises from Santa Cruz Island . The tortoises ' gigantism was probably a trait useful on continents that was fortuitously helpful for successful colonisation of these remote oceanic islands rather than an example of evolved insular gigantism . Large tortoises would have a greater chance of surviving the journey over water from the mainland as they can hold their heads a greater height above the water level and have a smaller surface area / volume ratio , which reduces osmotic water loss . Their significant water and fat reserves would allow the tortoises to survive long ocean crossings without food or fresh water , and to endure the drought @-@ prone climate of the islands . A larger size allowed them to better tolerate extremes of temperature due to gigantothermy . Fossil giant tortoises from mainland South America have been described that support this hypothesis of gigantism that pre @-@ existed the colonization of islands . 
