About 10 to 15 million years ago, an extinct species of side-necked turtle called Chelus colombiana inhabited the vast wetlands of what is now northern South America. A recently described shell from the Peruvian Amazon suggests that the species grew to enormous sizes. An artistic reconstruction of Colombian Chelus. Image credit: Juan Giraldo. First described in 1976, Chelus colombiana belongs to a genus of freshwater turtles in the family Chelidae. The genus is native to slow-flowing rivers, swamps and other aquatic habitats in northern South America. Its best-known member is the matamata tortoise (Chelus fimbriata), famous for its flattened, rough, highly camouflaged shell and strange, gnarled head and neck. The genus is adapted to a primarily aquatic lifestyle and includes turtles that ambush prey by rapidly expanding their throat and sucking water and prey into their mouths. “The Chelidae are the most diverse group of pleurodiran (side-necked) turtles extant, comprising at least 60 species,” said Dr. Edwin-Alberto Cadena, a researcher at Universidad del Rosario, the Smithsonian Tropical Research Institute and the Field Museum of Natural History, and his colleagues. “They are distributed throughout Australia, New Guinea, Indonesia and South America.” “The largest living chelid is Chelus fimbriata, and females, generally larger than males, reach a maximum straight carapace length of 52.6 cm (1.7 ft).” “However, the average shell length of adult females is approximately 29.5 cm (1 foot).” In a new study, Dr. Cadena and his co-authors examined two new fossil shells of Chelus colombiana. The largest specimen, cataloged as MUSM-920, measures 84.6 cm (2.8 ft) along its longest edge. Investigators estimate the individual weighed around 65 kg (143 lb). The MUSM-920 projectile was found in 2005 along the bank of the Inuya River in the Fitzcarrald Arc region of Peru. The second specimen, MUSM-5003, was found in 2010 in lignite deposits near Iquitos, in northern Peru. Both are held at the Natural History Museum of the Universidad Nacional Mayor de San Marcos in Lima. Chelus colombiana specimen MUSM-920 from the Middle Miocene of the Fitzcarrald Arc, Peru. Image credit: Cadena et al., doi: 10.1016/j.palwor.2026.201135. “Specimen MUSM-920 represents the largest fully preserved shell ever recorded for the genus and species,” the scientists said. “Its size is comparable to that of a partially preserved specimen from Brazil, which, based on the scale provided in the original study, measures 77.4 cm (2.5 ft) and is estimated to have reached approximately 90 cm (3 ft) in total length.” “Together, these specimens represent the largest known kelid tortoises ever recorded.” The findings extend the known range of Chelus colombiana, previously recorded in Colombia and Brazil, to the southwestern edge of the Pebas system, a huge complex of lakes, swamps and rivers that dominated the western Amazon during the Miocene. The specimens fit a broader pattern of gigantism among Miocene turtles in northern South America, attributed to the size and connectivity of the wetland system rather than climate. “Fossil localities in Venezuela, Colombia, Brazil and those recently identified in Peru continue to have significant potential to produce complete skeletons that could ultimately resolve the taxonomic controversy surrounding the Chelus fossil record,” the authors said. The findings appear in the October 2026 issue of the journal Palaeoworld. _____ Edwin-Alberto Cadena et al. 2026. New fossil material of Chelus (Testudines: Chelidae) from the Middle Miocene of Peru. Paleomundo 35 (5): 201135; doi:10.1016/j.palwor.2026.201135