A groundbreaking discovery of a 90-million-year-old fossil in Argentina is reshaping our understanding of the evolutionary history of a unique group of bird-like dinosaurs. This find helps settle a longstanding debate regarding their distribution across the ancient world.
The fossils detailed in Nature belong to Arunachetri seropolisiensis, a member of the Alvarezaurus family. This small dinosaur is characterized by its tiny teeth and stout arms, which end in a prominent single thumb claw.
While most well-preserved Alvarezsaurus fossils have been discovered in Asia, the existence of Alvarezsaurus in South America raises intriguing questions due to the vast ocean separating these continents.
A nearly complete skeleton uncovered at the La Buitrera fossil site in northern Patagonia has provided remarkable evidence regarding this species. This region was also home to primitive snakes and small saber-toothed mammals.
“Creating a nearly complete, articulated animal from a fragmented skeleton is akin to discovering the Rosetta Stone of paleontology,” stated Peter Makowiecki, a professor at the University of Minnesota, and the study’s first author.
Unlike their later relatives, Arunashetri had longer arms and larger teeth. This indicates that Alvarezsaurids likely reduced their body size before evolving the characteristic small limbs and teeth suited for an ant and termite diet.
“Our study suggests that alvarezsaurids form a compact group of dinosaurs, with species sizes ranging from crows to humans,” Makowiecki told BBC Science Focus. “Body size appears to fluctuate within this limited range without a clear trend.”
This discovery also addresses an intercontinental mystery. A detailed anatomical study of Arunashetri led Makowiecki and his team to examine fossil collections globally. “We found other Alvarezaurids hiding in plain sight,” he noted.
“These species, which existed during the Jurassic period in North America and the Early Cretaceous in Europe, enhance our understanding of Alvarezsaurus’s widespread presence prior to the major rift between the Northern and Southern Hemispheres.”
Approximately 200 million years ago, all of Earth’s continents formed a single supercontinent named Pangea. This landmass gradually fragmented over tens of millions of years, evolving into its current configuration while transporting its fauna along with it.
The research team is preparing additional specimens from the same site, though Professor Makowiecki has remained tight-lipped about their specifics. “The new specimen confirms some of our findings regarding size and specialization,” he disclosed. “Currently, we have no further plans.”
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Source: www.sciencefocus.com
