Paleontologists have identified a massive fossil shell of the extinct side-neck turtle Chelus colombiana in Peru, revealing a freshwater reptile that reached an estimated 84.6 centimeters in length and weighed roughly 65 kilograms approximately 10 to 15 million years ago during the Miocene epoch. The discovery marks the largest completely preserved shell ever recorded for the genus.
Excavation in the Peruvian Amazon Yields Record Shells
The largest of the two examined specimens, cataloged as MUSM-920, was recovered in 2005 along the margin of the Inuya River within Peru’s Fitzcarrald Arch region. A second specimen, designated as MUSM-5003, emerged in 2010 from lignite deposits near Iquitos in northern Peru. Both fossils are currently housed at the Museo de Historia Natural of the Universidad Nacional Mayor de San Marcos in Lima.
Researchers calculated that the MUSM-920 specimen stretched 2.8 feet along its longest edge. This physical dimension places the ancient reptile in a rarefied category of prehistoric giants. Freshwater turtles rarely achieve such extreme scales because constrained shell structures and metabolic limits usually cap their growth.
Wetland Connectivity Drives Miocene Gigantism
These Peruvian finds extend the known geographic range of Chelus colombiana. Earlier discoveries had mapped the extinct species to Colombia and Brazil. The new specimens tie the reptile directly to the Pebas system, a sprawling complex of lakes, swamps, and rivers that dominated western Amazonia during the Miocene epoch.
Dr. Edwin-Alberto Cadena, a researcher affiliated with the Universidad del Rosario, the Smithsonian Tropical Research Institute, and the Field Museum of Natural History, along with his co-authors, published the findings in the October 2026 issue of the journal Palaeoworld. The research team connected the exceptional size of these reptiles to the sheer scale and high connectivity of the ancient wetland network rather than to climate.
“The Chelidae are the most diverse group of extant pleurodiran (side-necked) turtles, comprising at least 60 species,” Dr. Cadena and his colleagues stated.
Modern side-neck turtles fold their necks sideways into their shells rather than pulling them straight back. Their best-known living relative, the matamata turtle (Chelus fimbriata), features a flattened, rough shell and a knobby head adapted to slow-moving waters. While modern adult female matamatas reach a maximum straight carapace length of 52.6 centimeters and average about 29.5 centimeters, the Miocene species far exceeded those dimensions.
Resolving Taxonomic Controversies in South American Paleontology
The new fossil material contributes to a broader pattern of gigantism observed among northern South American turtles during the Miocene. Scientists utilize these well-preserved shells to reconstruct ancient environmental conditions, including water availability and food supply, before the modern Amazon River and its floodplain took shape.
The research team emphasized that ongoing fieldwork across Venezuela, Colombia, Brazil, and Peru holds significant potential for uncovering complete skeletons. Such discoveries will be necessary to resolve lingering taxonomic debates surrounding the fossil record of the genus Chelus.
