 Mitochondrial DNA studies of tortoises on Santa Cruz show up to three genetically distinct lineages found in nonoverlapping population distributions around the regions of Cerro Monturra , Cerro Fatal , and La Caseta . Although traditionally grouped into a single subspecies ( C. n. porteri ) , the lineages are all more closely related to tortoises on other islands than to each other : Cerro Monturra tortoises are most closely related to G. n. duncanensis from Pinzón , Cerro Fatal to G. n. chathamensis from San Cristóbal , and La Caseta to the four southern races of Isabela as well as Floreana tortoises . 
