Scientists Just Found a 2-Pound Dinosaur That's Rewriting Evolution

A near-complete skeleton from Patagonia solves decades-old mysteries about one of the strangest dinosaur groups ever discovered.

TL;DR: Researchers have unveiled an almost complete skeleton of Alnashetri cerropoliciensis, a 90-million-year-old dinosaur that weighed less than 2 pounds. The discovery helps explain how alvarezsaurs—bizarre bird-like dinosaurs with single-clawed arms—evolved and spread across the ancient world.

What Is Alnashetri?

Alnashetri cerropoliciensis was a tiny theropod dinosaur belonging to the alvarezsaur family. These unusual creatures had:

• Extremely small body sizes (Alnashetri weighed less than 2 lbs)
• Tiny teeth
• Short arms ending in a single enlarged thumb claw

Scientists believe the specialized claw may have been used for breaking into termite mounds and ant nests—essentially making these dinosaurs the anteaters of the Cretaceous period.

Why This Discovery Matters

For decades, paleontologists struggled to understand alvarezsaurs because most well-preserved fossils came from Asia. South American specimens were fragmentary and hard to interpret.

The new Alnashetri skeleton, discovered in 2014 at the La Buitrera fossil site in northern Patagonia, Argentina, changes everything.

"Going from fragmentary skeletons that are hard to interpret, to having a near-complete and articulated animal is like finding a paleontological Rosetta Stone," said lead researcher Peter Makovicky from the University of Minnesota.

What the Skeleton Reveals

The nearly complete fossil—published this week in the journal Nature—shows that Alnashetri differed from its later relatives in several key ways:

1. Longer arms than specialized later species
2. Larger teeth than its ant-eating descendants
3. Already tiny body size despite lacking specialized features

This means alvarezsaurs became small before they evolved their distinctive insect-hunting adaptations—not the other way around.

Microscopic bone analysis confirmed the specimen was fully grown and at least four years old. Even at full maturity, it weighed less than 2 pounds, making it one of the smallest dinosaurs ever discovered in South America.

A Global Journey Across Pangaea

The research team also discovered something unexpected: alvarezsaurs appeared much earlier than scientists previously believed.

By examining additional fossils in museum collections across North America and Europe, researchers found evidence that these dinosaurs spread across the world when the continents were still connected as the supercontinent Pangaea.

Size Comparison: How Small Is 2 Pounds?

Why Tiny Dinosaurs Are So Important

Large dinosaur discoveries grab headlines, but small dinosaur fossils often provide more valuable scientific insights:

1. They preserve better — Smaller bones can be buried quickly and completely
2. They reveal evolutionary transitions — Size changes often precede other adaptations
3. They fill gaps in the family tree — Many dinosaur lineages had small ancestors we're only now discovering

The Alnashetri discovery proves that not all dinosaurs were giants—and some of the most interesting ones could fit in your hand.

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