Scientists have discovered a remarkably complete fossil of a tiny dinosaur that is helping to solve a long-standing puzzle about a strange group of prehistoric animals.
The fossil, about 90 million years old, belongs to a species called Alnashetri cerropoliciensis. Researchers say it provides a crucial “missing link” for understanding a mysterious family of bird-like dinosaurs known as alvarezsaurs.
The international research team, led by scientists from the University of Minnesota and Argentina, described the discovery in the journal Nature.
Alvarezsaurs have puzzled scientists for decades because most well-preserved fossils were found in Asia, while the few remains discovered in South America were incomplete and difficult to interpret.
This new specimen, found in northern Patagonia, Argentina, is nearly a full skeleton, allowing scientists to finally see how these animals were built.
The fossil was first uncovered in 2014 at the La Buitrera site, an area famous for exceptionally preserved fossils from the Cretaceous period.
Preparing the delicate bones took years of careful work to avoid damaging them. Once assembled, the skeleton revealed important clues about how alvarezsaurs evolved and spread across the ancient world.
Alvarezsaurs are known for their unusual appearance. They were small, bird-like dinosaurs with tiny teeth and short arms that ended in a single large claw, possibly used to dig into insect nests.
However, Alnashetri looked somewhat different from its later relatives. It had longer arms and larger teeth, showing that these dinosaurs became tiny before developing the specialized features linked to eating ants and termites.
Microscopic examination of the bones showed that the fossil belonged to an adult animal at least four years old. Despite being fully grown, it weighed less than two pounds, making it one of the smallest dinosaurs ever found in South America. Even the largest members of its group were only about the size of a human, which is small compared with most dinosaurs.
The discovery also helped scientists trace the origins of alvarezsaurs. By comparing the new fossil with older museum specimens from North America and Europe, the team concluded that these animals appeared earlier than previously thought, when Earth’s continents were still joined together as the supercontinent Pangaea. As the continents drifted apart, the dinosaurs became separated and evolved in different regions rather than traveling across oceans.
The fossil was preserved in remarkable condition because the animal was quickly buried by a moving sand dune, protecting the skeleton for millions of years. The La Buitrera site has produced many other important fossils, including early snakes and small saber-toothed mammals, offering a rare glimpse into ecosystems dominated by tiny animals.
Researchers believe there is more to discover. Fossils from the same area are still being studied, and scientists say they may reveal further chapters in the story of these unusual dinosaurs.
This tiny dinosaur may have been small in size, but its discovery is making a big impact—helping scientists better understand how bird-like dinosaurs evolved, adapted, and spread across the prehistoric world.
