A tiny tooth from Argentina ends a decades-long debate about ancient mammal history

Nature · Published 3 October 2026 Swipe more like this →

In short: For years, paleontologists argued whether multituberculates, a successful group of rodent-like mammals, ever inhabited South America. A newly discovered molar from Patagonia finally settles the dispute. It confirms that these diverse, omnivorous creatures coexisted with other unique southern mammals, rewriting our understanding of their global distribution during the Late Cretaceous.

Multituberculates were a remarkably successful order of mammals, thriving from the Middle Jurassic through the late Eocene. Named for the multiple tubercles on their teeth, these animals occupied diverse ecological niches, ranging from burrowing to arboreal lifestyles. While their fossil record is exceptionally well-documented in Laurasia, their presence in Gondwanan landmasses—including South America—has long been a subject of intense scientific debate.

In South American paleontology, the confusion stemmed from the discovery of Gondwanatheria, a distinct group of allotherian mammals. Because no definitive multituberculate molars had been found in the region, fossils like Argentodites coloniensis were often reclassified as ferugliotheriids, a type of gondwanatherian. This led many researchers to conclude that multituberculates were absent from the continent entirely, despite their global success elsewhere.

The discovery of Notopolytheles joelis, a new genus and species identified from a left upper first molar in Argentina’s La Colonia Formation, provides the first unambiguous evidence of a multituberculate in South America. The specimen displays the characteristic three-row cusp configuration of the Cimolodonta subgroup. By confirming that Notopolytheles joelis is indeed a multituberculate, researchers have resolved the long-standing uncertainty, proving that both multituberculates and gondwanatherians coexisted in the Late Cretaceous of Patagonia.

This finding is significant because it highlights the high level of endemism in South American mammals during the Maastrichtian age. The unique dental features of Notopolytheles joelis, such as its specific cusp formula and root structure, distinguish it from other known cimolodontans. This discovery not only clarifies the taxonomic status of previously debated fossils but also provides a clearer picture of the complex mammalian landscape that existed before the end of the Cretaceous period.

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