Discover the fascinating skeleton of the Alvarezauroid dinosaur species Arunachetri seropolisiensis. This groundbreaking find includes two specimens from Patagonia, Argentina, along with two from the Northern Hemisphere, providing insights into how this enigmatic lineage of theropod dinosaurs evolved and dispersed before the separation of continents, challenging established beliefs regarding its origins.

Learn more about Arunachetri seropolisiensis, which thrived in Argentina during the Cenomanian period of the Late Cretaceous, approximately 90 million years ago.

This species was initially described from partial remains in 2012 and is categorized under Alvarez Sauroidea.

These unique small dinosaurs are noted for their tiny teeth and short arms, each ending in a prominent thumb claw.

“The Alvarezauroidea represents a mysterious clade of mainly small theropod dinosaurs, primarily found in the Jurassic to Cretaceous periods of Asia and South America,” states paleontologist Peter Makowiecki from the University of Minnesota, Twin Cities, along with his research team.

“Late Cretaceous Alvarezauroids are believed to have been carnivorous, primarily consuming ants, and possessing specialized forelimbs suitable for digging, microscopic supernumerary teeth, and heightened sensory abilities.”

“They are thought to have undergone evolutionary miniaturization alongside dietary specialization.”

The almost complete skeleton of Arunachetri seropolisiensis was discovered in the La Buitrera fossil site in Rio Negro, northern Patagonia.

Microscopic examination confirmed that this specimen was an adult, estimated to be at least four years old.

Weighing less than 0.9 kg (2 lb), it ranks as one of the smallest-known dinosaurs from South America.

In contrast to its later relatives, Arunachetri seropolisiensis featured longer arms and larger teeth.

Paleontologists conclude this indicates that some alvaresaurids transitioned into smaller forms well before they developed adaptations for an ant-based diet.

Researchers, by analyzing previously discovered alvaresaurid fossils housed in museums across North America and Europe, further demonstrate that these dinosaurs originated earlier than previously presumed, existing during the period when the continents were still part of the supercontinent Pangaea.

Their distribution appears to have resulted from the fragmentation of Earth’s landmass, making ocean crossings unlikely.

“Our biogeographical study suggests a Pangean ancestral distribution for Alvarezsauroroidea, indicating that the clade’s early history was primarily influenced by surrogates,” the scientists remarked.

Read their groundbreaking research in the paper published in Nature.

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PJ Makowiecki et al.. Discovery in Argentina reshapes the evolutionary narrative of a fascinating dinosaur clade. Nature published online on February 25, 2026. doi: 10.1038/s41586-026-10194-3