Tiny dinosaur discovery in land of giants

About 95 million years ago in Argentina's Patagonia region of South America, giant dinosaurs ruled the land.

There was Giganotosaurus, a huge, fearsome meat-eater, and Argentinosaurus, a plant-eater that may have tipped the scales at a staggering 70 tonnes, that's the weight of about 12 African Elephants!

But Patagonia wasn't just home to giants. Scientists have now discovered one of the smallest-known dinosaurs ever: Alnashetri cerropoliciensis.

"When we think of landscapes with dinosaurs… we picture enormous beasts roaming the distance. But these landscapes were full of medium and small animals too," said palaeontologist and study co-author, Sebastián Apesteguía.

"Alnashetri shows us that it wasn't just a time of giants, but a time of incredible biodiversity."

This tiny dinosaur, nicknamed "Alna," was only about the size of a crow.

It probably hunted small creatures such as lizards, snakes, tiny mammals, and insects. What makes Alna special is that its skeleton is nearly complete and very well preserved, with the bones still in the positions they would have been in life.

Alnashetri belongs to a group of dinosaurs called alvarezsaurs. These were small, meat-eating dinosaurs that are part of a much bigger dinosaur group called theropods. Theropods include famous predators like Tyrannosaurus rex and Velociraptor, as well as the ancestors of modern birds.

Alna is such an early and well-preserved member of the alvarezsaurs, so it helps scientists understand how this unusual group of dinosaurs first evolved and how some of them later changed to become specialised insect-eaters.

Alna's fossil was found in La Buitrera, a sandstone site in northern Patagonia's Río Negro Province in central Argentina.

Known as the Kokorkom Desert (or "Desert of the Bones" in the indigenous Mapuche language) it was a prehistoric sand-dune field that existed approximately 95 to 100 million years ago.

The area has produced many fossils of small and medium-sized animals from the Cretaceous Period. Alna was a small female who lived in a desert environment and died at about four years old, nearly fully grown.

Her body was quickly covered by sand, which is why her bones are so well preserved.

Alna had strong, pointy teeth like a small Velociraptor, and her tail was very long compared with her body. Her arms were well-developed, but too short to fly. Scientists could even study the microscopic structure of her bones to learn about her growth.

"Although many of the inhabitants of the Kokorkom Desert were burrowers, Alnashetri was a lightweight animal that moved across the dunes on its slender legs. Its body resembled that of a rooster, but with a long tail," said palaeontologist, Sebastián Apesteguía.