MINNEAPOLIS / ST. PAUL (02/25/2026) — A team co-led by University of Minnesota Twin Cities researcher Peter Makovicky and Argentinean colleague Sebastian Apesteguía has identified a 90-million-year-old fossil that provides the “missing link” for a mysterious group of prehistoric animals.
The study, published in the peer-review journal Nature , details the discovery of a complete skeleton of Alnashetri cerropoliciensis. Alnashetri belongs to a group of bird-like dinosaurs, known as alvarezsaurs, that are famous for their tiny teeth and stubby arms ending in a single large thumb claw. For decades, they have remained a mystery because most of the well-preserved fossils were found in Asia, while records from South America were fragmented and difficult to interpret.
In 2014, the almost complete fossil of Alnashetri was discovered in the northern part of Patagonia, Argentina, at a site that is world-renowned for its exquisite Cretaceous fossils. The species was originally named a few years prior based on fragmentary remains, but this newer, more complete specimen allowed the team to finally map the group's strange anatomy. The team spent the last decade carefully preparing and piecing together the fossils to avoid damaging the small bones.
“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 Peter Makovicky, lead author on the paper and a professor in the University of Minnesota Department of Earth and Environmental Sciences. “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.”
The discovery of this nearly complete skeleton opens up a new understanding of how its lineage evolved, shrank and spread across the ancient world.
Unlike its later relatives, Alnashetri had long arms and larger teeth. This proves that some alvarezsaurs evolved to be tiny long before they developed these specialized features thought to be adaptations for an "ant-eating" diet.
Microscopic analysis of the bones confirmed the animal was indeed an adult of at least four years old. These animals are not just among the tiniest non-avian dinosaurs, but they never get any bigger—the largest species are the size of an average human, very small for dinosaurs, and Alnashetri itself weighed less than 2 lbs making it one of the smallest dinosaurs known from South America.
By identifying previously found alvarezsaurs fossils in museum collections from North America and Europe, the team proved these animals originated much earlier than expected when the continents were still connected as the supercontinent Pangaea. Their distribution was caused by the breakup of the earth's landmasses, not unlikely treks across oceans.
The well-preserved fossil was recovered from the La Buitrera fossil area, a site that has yielded other scientifically critical animals, including primitive snakes and tiny saber-toothed mammals.
“After more than 20 years of work, the La Buitrera fossil area has given us a unique insight into small dinosaurs and other vertebrates like no other site in South America," said Apesteguía, a researcher at Universidad Maimónides in Buenos Aires, Argentina.
Their work is far from over, as the scientists continue to discover and study fossils from the same area where they discovered Alnashetri. “We have already found the next chapter of the alvarezsaurid story there, and it is in the lab being prepared right now,” added Makovicky.
In addition to Makovicky and Apesteguía, the international team included Jonathan S. Mitchell from Coe College in Iowa; Jorge G. Meso and Ignacio Cerda from Instituto de Investigación, Universidad Nacional de Río Negro and Museo Provincial; and Federico A. Gianechini from Instituto Multidisciplinario de Investigaciones Biológicas de San Luis.
The research was supported by the National Scientific and Technical Research Council (CONICET), The Field Museum, National Geographic, University of Minnesota, United States National Science Foundation and the Fulbright U.S. Scholar program.
Read the full paper entitled, “Argentine fossil rewrites evolutionary history of a baffling dinosaur clade,” on the Nature website
Nature
Argentine fossil rewrites evolutionary history of a baffling dinosaur clade
25-Feb-2026