(C) El Pais

PATAGONIA, ARGENTINA — In a discovery that is reshaping our understanding of prehistoric life, paleontologists have unveiled a near-complete skeleton of a dinosaur that weighed less than a kilogram. The fossil of Alnashetri cerropoliciensis, a 90-million-year-old creature no larger than a modern-day chicken, suggests that some dinosaur lineages didn't just "shrink" over time—they started small.

A Paleontological "Rosetta Stone"
The research, led by Professor Peter Makovicky of the University of Minnesota and published in the journal Nature, focuses on a specimen unearthed in Northern Patagonia. While the species was previously known only through fragmented remains, this newly analyzed, articulated skeleton provides an unprecedented look at its unique anatomy.

"Finding a near-complete, articulated fossil in a field of fragmented bones is like finding the Rosetta Stone for this lineage," said Makovicky. The high-resolution microscopic analysis confirmed a startling fact: this tiny creature, weighing approximately 900g, was at least four years old—a fully grown adult.

Challenging the "Miniaturization" Myth
For nearly two decades, the scientific community adhered to a theory that the Alvarezsauridae family (the group to which Alnashetri belongs) gradually evolved to be smaller as they shifted their diet to ants and termites. However, Alnashetri turns this theory on its head.

Unlike its later descendants, which featured stump-like arms and specialized claws for digging into insect mounds, Alnashetri possessed relatively long arms and sharp teeth. This suggests it was a predator of small vertebrates rather than an insectivore.

"Alnashetri is the smoking gun proving that the perceived trend of gradual miniaturization did not exist in the way we thought," explained co-author Dr. Jorge Meso. "These dinosaurs were already exceptionally small long before they adapted to a diet of insects."

From Pangaea to the World
The study also sheds light on the global distribution of these theropods. By comparing the Patagonian find with fossils held in North American and European museums, the team demonstrated that these dinosaurs existed when the Earth's landmasses were still joined as the supercontinent Pangaea.

Rather than crossing vast oceans, the ancestors of Alnashetri were likely dispersed across the globe by the literal drifting of continents. This placement firmly roots them as close relatives of the Tyrannosauroidea lineage, despite the staggering difference in scale.

The Next Chapter
The discovery of Alnashetri provides a vital link between large-bodied theropods and the specialized, tiny insect-eaters of the late Cretaceous. As researchers continue to prepare more fossils from the Patagonian site, the "next chapter" of the Alvarezsaur story promises to reveal even more about how size and diet influenced the survival of the most successful predators in Earth's history.