Paleontologists have unearthed the fossilized lower right canine tooth of a significant proborchiid Sparathodont in Brazil’s Taubaté Basin.

The newly discovered fossils date back to the Oligocene Desedan period, approximately 29 to 21 million years ago.

This specimen has been classified as a yet unnamed member of the Proborhyaenidae, an extinct family of South American mammals within the Metatherian order of Sparassodonta.

These creatures played the role of carnivorous predators on the Cenozoic continents.

“Sparassodonta represents an extinct clade of metatherians exclusive to South America, which served as the primary predator of terrestrial mammals on this continent throughout the Cenozoic era,” noted paleontologist Dr. Caio César Rangel from the Federal University of Uberlandia and the Federal University of Pernambuco and colleagues.

“Their evolutionary journey included two significant diversification events, first during the Eocene and later in the Miocene.”

“The Oligocene is marked by cooler temperatures compared to the late Eocene and Miocene.”

“This global cooling trend led to substantial environmental changes, resulting in a turnover in fauna across South America, including both extinctions and diversifications among various Metatherian clades.”

Reconstruction of Thylacosmilus atrochus, a type of post-saber-toothed beast that is part of the sister lineage to the Proborhyaenidae. Image credit: Roman Uchytel.

Paleontologists retrieved the new specimen, measuring 5.73 centimeters (2.3 inches) in length, from the lower section of the Tremembé Formation in São Paulo state, eastern Brazil.

The researchers explained, “The Taubate Basin is situated in São Paulo in southeastern Brazil, stretching from the city of Cachoeira Paulista to Jacarei.”

“It measures approximately 150 km (93 miles) in length and 10–20 km (6–12 miles) in width and lies within a rift between the Serra do Mar and Serra da Mantiqueira mountains.”

“The Tremembé Formation is the sole Late Oligocene fossil site in Brazil that preserves a diverse array of mammalian fossils and native species,” they added.

“The fauna within this area includes representatives from Metatheria, Pteroptera, Rodentia, Singleta, Astrapoteria, Litopterna, Notungulata, and Pyrotheria.”

This ancient predator thrived in wetland and lake environments and is believed to have held the position of apex predator.

The researchers noted, “The observable wear on the crown and the associated undulations found on the canines indicate that their frequent use is likely related to the capture or active processing of prey by adult specimens.”

This discovery broadens the geographic distribution of Proborhyaenidae and marks the second record of this member of the Sparasodontidae in Brazil.

“This record enhances the diversity of large mammals found in the Tremembé Formation,” the authors stated.

“In general, this region serves as a crucial geological and paleontological resource that offers valuable insights into the final phases of the Paleogene period in tropical South America.”

For more about this discovery, refer to the published paper in the August 2025 issue of Revista Brasileira de Paleontology.

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CC Rangel et al. 2025. The “swamp monster” of the Tremembé Formation (Taubaté Basin, Brazil, late Oligocene): description of a carnivorous metatherian (Sparasodonta, Proborhyaenidae). Revista Brasileira de Paleontology 28 (2): e20250534; doi: 10.4072/rbp.2025.2.0534