A new study of a remarkably well-preserved fossil, found in northern Patagonia, Argentina, and dating to 90 million years ago, reveals one of the smallest dinosaurs ever found.

Tiny Dinosaur Fossil Found

Though researchers previously discovered Alnashetri, a little dinosaur that ate bugs and weighed less than a hedgehog, the recent study reveals the Alnashetri cerropoliciensis fossil, a new and almost complete specimen, which is a very rare and exciting find for paleontologists.

“We now have a reference point that allows us to accurately identify more scrappy finds and map out evolutionary transitions in anatomy and body size,” said Peter Makovicky, lead author of the study and a professor in the University of Minnesota Department of Earth and Environmental Sciences, in a statement this week.

“Going from fragmentary skeletons that are hard to interpret, to having a near complete and articulated animal is like finding a paleontological Rosetta Stone,” he said.

The dinosaur reportedly had long arms, ending in a single thumb claw, and, despite the specimen being an adult, it only weighed 2 pounds. The creature’s unique proportions imply that it was a stepping-stone species. The creature’s size also implies that dinosaurs didn’t evolve to become small because of their diet, but rather that the diet was adapted to their size.

This new find also helps to answer the larger question of why alvarezsaur fossils have been found in both South America and Asia, which are separated by a vast ocean.

Inspired by the Patagonian find, the team took another look at fossil collections in Europe and North America, and “we found other alvarezsaurs hiding in plain sight,” Makovicky told BBC Science Focus. “These species […] helped prove that alvarezsaurs were inhabiting most of the continents before the major rifts between the northern and southern hemispheres occurred.”

The study is published in Nature.