(CN) - High in the Andes mountains of northwestern Argentina, at an elevation of nearly 10,000 feet, paleontologists unearthed a fossil that offers rare insight into how small, short-necked dinosaurs gave rise to the towering, long-necked giants that would eventually dominate the Mesozoic planet.
The discovery, reported Wednesday in Nature, offers a snapshot in to the evolution of sauropodomorphs - a group that would later include some of Earth's largest land animals.
The fossil was found in the Santo Domingo Formation in Quebrada Santo Domingo, La Rioja province. At more than five feet long and weighing 40 pounds, paleontologists say Huayracursor jaguensis was significantly larger than its earliest relatives, which weighed around 20 pounds.
Huayracursor jaguensis - which combines the Quechua word for "wind" with the Latin for "runner" - is estimated to have lived about 231 million years ago during the Late Triassic period.
"This discovery provides one of the oldest pieces of evidence of increased body mass and neck elongation in early Sauropodomorpha," authors from Argentine research institutions say in the study.
They say the dinosaur's neck bones show clear signs of getting longer, even though its overall neck remained relatively short compared to later sauropodomorphs. This detail suggests that the evolutionary changes that would eventually produce the iconic long-necked dinosaurs like the Brachiosaurus were already underway in these early species.
The discovery also expands the known geographic range of early dinosaurs. Until now, most evidence of dinosaur evolution from this period has been confined to two basin regions: the Ischigualasto-Villa Union Basin in Argentina and the Parana Basin in Brazil. The Santo Domingo Formation represents a different geological setting, formed independently from these previously studied areas.
The Late Triassic period, spanning roughly 237 to 201 million years ago, was a time of major ecological change. Ecosystem transformations gave rise to the spread of dinosaurs, early mammal relatives and the group that includes modern crocodiles.
Understanding how and where these animals evolved has been difficult because of the limited number of fossil sites from this era.
The research team's analysis of evolutionary relationships places Huayracursor as a transitional form between the smallest early sauropodomorphs and larger species that would emerge in the Norian age of the Late Triassic.
"Our phylogenetic analysis, based on a recent matrix, recovers Huayracursor deeply nested within Sauropodomorpha, as the sister taxon of Bagualosaurus," the researchers write.
The study challenges previous assumptions about how sauropodomorphs evolved their distinctive features. Rather than neck elongation and increased body size occurring as separate developments happening one after the other, the evidence from Huayracursor suggests these traits evolved together.
"Huayracursor stands out among the oldest sauropodomorphs for its large body size, surpassing its contemporaries from the Ischigualasto Formation and reaching a mass comparable to Bagualosaurus," the researchers said.
The Santo Domingo Formation has also yielded other fossils that paint a picture of a diverse Late Triassic ecosystem.
"The QSD faunal assemblage further includes diverse archosauromorphs and synapsids typically found globally in Carnian strata," according to the researchers, including rhynchosaurs, cynodonts, and aetosaurs that closely resemble fauna found in the better-studied Ischigualasto Formation.
The researchers estimate that the major developments in neck elongation and body mass in early sauropodomorphs may have occurred within a 5- to 8-million-year window between the Carnian and Norian, a relatively rapid evolutionary timeframe.
As paleontologists continue to explore less-studied fossil sites like the Santo Domingo Formation, discoveries like Huayracursor are reshaping our understanding of dinosaur evolution.
"Future research should further explore the diversity of this unique assemblage, providing new insights into the early evolution of several tetrapod lineages," the researchers wrote.
Source: Courthouse News Service
