Scientists reveal the oldest long-necked dinosaur fossil ever discovered

High in the Andes, researchers braved rugged terrain and unpredictable weather in search of clues to the geological history of an ancient basin. They discovered something that changed the course of their expedition – the world’s oldest fossil of a long-necked dinosaur.

As it turned out, their discovery changed our understanding of the evolution of these prehistoric giants. The fossil consisted of a nearly complete fossilized skeleton of a new sauropodomorph species – part of the long-necked, plant-eating group. 

The 1.5-meter (5-foot) tall dinosaur lived around 230 million years ago during the Late Triassic period. This places it among the oldest sauropodomorphs ever discovered.

Naming Huayracursor jaguensis

The researchers named it Huayracursor jaguensis. The genus name Huayracursor means “wind runner,” which suggests that it was a swift animal. The species name honors Jagüé village near the discovery site in La Rioja, Argentina.

Huayracursor had a much longer neck and was larger than its Late Triassic peers. The researchers say that this distinction offers the earliest proof that two evolutionary changes were happening at once in sauropodomorphs at that time: they were growing longer necks and larger bodies.

The dinosaur fossil was found in Argentina’s Quebrada de Santo Domingo. For the researchers, this site was familiar ground from earlier expeditions to the largely unexplored area west of La Rioja province. 

Their work revealed the region’s fossil-rich nature. In the past 10 years, it has given the world dinosaurs and other Triassic reptiles, as well as mammal ancestors.

For the current study, the team’s initial aim was to improve the understanding of the Quebrada de Santo Domingo region, which was mostly unexplored.

They wanted to know how these rocks were linked to nearby geological systems, especially the well-studied Ischigualasto–Villa Unión Basin.

New window into Triassic life 

In terms of South American faunal discoveries, certain areas had dominated for more than half a century. These included Ischigualasto Provincial Park in Argentina and Rio Grande do Sul in Brazil. 

“This new region, within a virtually unexplored geological basin, opens up the prospect of major discoveries. It is rare to find entirely new sites with fauna so remarkably well preserved and abundant,” remarked Agustín Martinelli, co-author of the research paper, and a researcher at the National Council for Scientific and Technical Research (CONICET).

This fossil-rich site provides researchers with a rare opportunity to examine the ages of fossils. It also sheds light on significant ecosystem changes that took place on Earth during the Late Triassic.

Evolution of Huayracursor jaguensis

About 234 to 232 million years ago, Earth’s land and oceans underwent major changes. This period, known as the Carnian stage of the Late Triassic, witnessed a major climate shift. Changes occurred that reshaped ecosystems worldwide, leading to significant biodiversity loss.

As life on Earth began to recover from the damage, surviving species radiated and evolved. This led to the rise and spread of early mammals, crocodile relatives, and dinosaurs.

Finding the fossil long-necked dinosaur has changed older ideas about how these early giants evolved. 

For a long time, paleontologists believed that early sauropodomorphs were small and short-necked. Then, over several million years, they evolved into creatures with longer necks and larger bodies. 

A closer look at the Huayracursor fossil revealed a different story. The dinosaur’s longer neck and larger size, when compared to other dinosaurs of the era, pushed back the timeline of sauropodomorph evolution. It confirmed that these features appeared far earlier than scientists had previously believed.

Dating Huayracursor jaguensis

The researchers estimated when Huayracursor jaguensis lived by dating rocks from the lower section of the Santo Domingo Formation, where the fossil was found. They used two main techniques to deduce the age.

The first was biostratigraphy, where researchers examined the fossils found alongside Huayracursor. These included other reptiles, and early mammal relatives.

The same animals appear in other rock layers that were found to be roughly 237–227 million years old.

The second was radiometric dating. This method uses radioactive decay and its byproducts to find the age of rocks and geological formations.

For this study, they dated a volcanic rock layer higher in the Santo Domingo Formation, which turned out to be 212 million years old.

Since Huayracursor was found in a rock layer below this, it must be older than 212 million years. This places the fossil in the earlier Carnian stage of the Late Triassic.

Standing tall among peers

The fossil skeleton of Huayracursor jaguensis was found high up in the Andes, at an altitude of 3,000 meters (9,842 feet).

Although not complete, the fossil included parts of the skull, the limbs, and a full vertebral column extending to the tail. 

It is one of only two known Carnian-age sauropodomorphs from this period with a well-preserved hand. By assembling the fossil fragments, scientists found that Huayracursor was nearly 5 feet tall (1.5 meters) and weighed close to 40 pounds (18 kilograms). 

While 40 pounds pales when compared to the popular images of dinosaurs towering like skyscrapers, it was nearly double the weight of its closest relatives.

The longer fourth and fifth vertebrae show early signs of neck elongation. The length-to-width ratios of the neck bones were between 4.2 and 2.2.

These values were higher than those of earlier forms but not yet as extreme as the later, long-necked species.

These combined features reveal that Huayracursor had been undergoing neck elongation and body bulking since the dawn of the sauropodomorph evolutionary story.

Lessons from Huayracursor jaguensis

The fossil discovery in the ancient basin has changed our understanding of the dinosaur evolution timeline. It also showed how this basin relates to other Triassic regions.

“Based on stratigraphic and sedimentological studies, we were able to recognize that the Triassic terrains of the Northern Precordillera belong to a sedimentary basin that evolved independently of other basins in southwestern Gondwana,” stated Sebastián Rocher, a CONICET researcher and one of the authors of the study.  

The team believes that these insights will encourage exploration farther west into the Andes Mountains. Fossils unearthed there may offer new clues about how ancient animals adapted and evolved during the Late Triassic.

The full study is published in the journal Nature. 

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