While Argentina’s ancient Patagonia region is synonymous with colossal dinosaurs like the fearsome meat-eating Giganotosaurus, weighing around eight tons, and the immense, long-necked plant-eater Argentinosaurus, potentially 70 tonnes, a recent discovery reveals a far more diminutive inhabitant of this prehistoric landscape.
Researchers have unearthed a remarkably well-preserved and nearly complete skeleton of one of the world’s smallest known dinosaurs, named Alnashetri cerropoliciensis. This creature, roughly the size of a crow, likely preyed on small animals such as lizards, snakes, mammals, and invertebrates.
The fossil, with its bones positioned as they would have been in life, offers crucial insights into alvarezsaurs, an unusual family of dinosaurs within the theropod group, which encompasses all meat-eating dinosaurs.
This specimen, affectionately nicknamed “Alna,” was discovered in sandstone at La Buitrera, a site in northern Patagonia’s Rio Negro Province renowned for yielding numerous small- and medium-sized animal fossils from the Cretaceous Period.
Alna was a small female that lived in a desert environment and died at the age of four, almost fully grown. Its exceptional preservation is attributed to its body being swiftly covered by a sand dune after its death.
Beyond birds, which evolved from small feathered dinosaurs, Alnashetri stands as the most diminutive dinosaur known from South America and rivals the smallest discoveries globally.
“Alnashetri is truly tiny. Weighing in around 0.7 kg (1.5 pounds), it is smaller than a chicken,” stated University of Minnesota paleontologist Peter Makovicky, lead author of the research published in the journal Nature. “It wouldn’t even reach knee height on an average adult person.”
Alvarezsaurs were typically small, characterised by stubby yet powerful forelimbs, long and slender hindlimbs, and lightly built skulls. Based on other Alvarezsaur fossils, researchers suspect Alnashetri was feathered. Despite possessing some bird-like characteristics, alvarezsaurs were only distantly related to birds.
Alna inhabited a locale known as the Kokorkom, meaning “desert of the bones” in the indigenous Mapuche language.
“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,” explained paleontologist and study co-author Sebastián Apesteguía of the Felix de Azara Foundation and Argentina’s National Scientific and Technical Research Council (CONICET).
“Its arms were well-developed, though not long enough to allow it to fly, and its tail, although not fully preserved, appears to have been as long (relative to body size) as that of any other typical carnivorous dinosaur,” Apesteguía added, estimating Alnashetri’s total length at about 70 cm (28 inches), with most of that being tail.
Alna’s delicate and fragile skeleton was so impeccably preserved that researchers were able to conduct histological examinations, studying its microscopic bone structures. “The level of histological detail is exquisite,” Apesteguía remarked.
Its numerous, strong, and pointy teeth were reminiscent of a small Velociraptor. Later alvarezsaurs from Argentina and elsewhere developed tiny teeth and reduced arms equipped with a large claw, presumably for digging into termite mounds as part of an insectivorous diet.
Alna demonstrates the existence of very small alvarezsaurs without an insect-eating specialisation, indicating that size reduction evolved multiple times within this lineage, Apesteguía noted.
The first remains of Alnashetri, two incomplete legs, were discovered in 2004 at La Buitrera. The current, more complete specimen was found in 2014 and underwent 12 years of meticulous preparation and study.
Patagonia remains a global hotspot for dinosaur fossils, both large and small. La Buitrera, in particular, has proven a goldmine for small vertebrates, including the limbed early snake Najash, the saber-toothed mammal Cronopio, and the small herbivorous reptile Priosphenodon, alongside other small dinosaurs like Jakapil and Buitreraptor.
“When we think of landscapes with dinosaurs, or through the lens of film fiction, we picture vast expanses with enormous beasts roaming in the distance. But these landscapes are almost always devoid of a crucial component of the ecosystem: medium and small animals,” Apesteguía said.
“The era in which Alnashetri, one of the smallest dinosaurs, lived coincided with what we often call the ‘age of the southern giants.’ Alnashetri shows us that it wasn’t a time of giants, but rather a time of immense biodiversity,” he concluded.
