Tiny Dinosaur, Big Impact: New Fossil Rewrites the Evolutionary History of an Enigmatic Clade
The Discovery
A groundbreaking study published in Nature reveals the significance of a 90-million-year-old fossil found in the Candeleros Formation of Neuquén Province, Argentina. The specimen belongs to Alnashetri cerropoliciensis, a tiny, bird-like dinosaur that is fundamentally changing how paleontologists view the evolution of the Alvarezsauroidea—a group of dinosaurs known for their bizarre, one-clawed hands and small stature.
Breaking the "Linear Miniaturization" Myth
For decades, it was widely accepted that alvarezsauroids followed a linear path of shrinking over time, starting as large predators and ending as tiny, specialized insectivores. However, the discovery of this exceptionally complete skeleton proves that:
Early Diversity: Alvarezsauroids already possessed small bodies and specialized features early in their history.
Non-Linear Evolution: Miniaturization happened repeatedly across different lineages rather than as a single, one-way event.
Global Presence: The presence of Alnashetri in South America indicates that these dinosaurs were widespread across the supercontinent of Gondwana much earlier than previously estimated.
Key Features and Anatomy
Despite being roughly the size of a chicken, Alnashetri was a highly capable predator. Unlike its later relatives who had almost entirely lost their fingers, Alnashetri retained longer arms and specialized hindlimbs.
"This fossil provides a missing link," says lead author Peter J. Makovicky. "It shows that the specialized traits we once thought were 'advanced' were actually part of a much older and more complex evolutionary toolkit."
Fact Sheet: Alnashetri cerropoliciensis
Period: Late Cretaceous (~90 million years ago)
Weight: Estimated under 2.2 lbs (1 kg)
Diet: Likely specialized insectivore or small vertebrate hunter
Key Finding: Disproves the theory of progressive miniaturization in theropod dinosaurs.
Source
Makovicky, P. J., Mitchell, J. S., Meso, J. G., et al. (2026). "Argentine fossil rewrites evolutionary history of a baffling dinosaur clade." Nature.
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