In 2016, a local man named Thanom Luangnan was walking near a drying pond in Chaiyaphum Province, in the arid northeast of Thailand, when he noticed something that didn’t look right.

There were bones exposed in the dirt at the edge of the water. They were unmistakably large. Not the bones of anything currently alive in the neighbourhood. Not the bones of anything anyone in his village had ever seen.

He reported them to local authorities. Word made its way to Mahasarakham University, and from there to a group of paleontologists who understood immediately what they might be looking at.

Ten years later, researchers described the fossils as a new long-necked dinosaur from what is now Thailand, dating to roughly 100–120 million years ago. The Scientific Reports paper estimated a mass of 25–28 tonnes and reported a length of about 27 metres, describing it as the largest dinosaur yet reported from Southeast Asia.

They named it Nagatitan chaiyaphumensis. The genus name honours the Naga, the mythological aquatic serpent of Southeast Asian folklore.

What it took to confirm

The cultural version of dinosaur discovery is a fast one — a fossil is found, and pretty soon a scientist on the news is holding up a bone and announcing a new species. The reality is much slower.

Fieldwork at the Chaiyaphum site continued across multiple field seasons between 2016 and 2019, with additional excavations happening as recently as 2024. The bones the team recovered included vertebrae, ribs, sections of pelvis, and leg bones. One of the front leg bones alone measured 1.78 metres — nearly six feet.

Once the bones came out of the ground, the slower work began. They had to be cleaned, stabilised, catalogued. They had to be measured, photographed, scanned. They had to be compared against the enormous existing catalogue of sauropod fossils from around the world, to determine what family they belonged to and whether the animal they had come from was actually new.

The research was led by Thitiwoot Sethapanichsakul, a PhD student at University College London, working with colleagues at Mahasarakham University, Suranaree University of Technology, and the Sirindhorn Museum in Thailand.

By the time the paper was published in Scientific Reports in May 2026, it had been ten years since Thanom Luangnan first noticed the strange bones by the pond.

What Nagatitan actually was

Nagatitan belonged to a family of sauropods called Euhelopodidae — a group of long-necked, plant-eating dinosaurs whose members are found only in Asia. Its close cousins, the titanosaurs, are found on every continent, including Antarctica. But the euhelopodids are Asia’s own contribution to the family of dinosaur giants.

In life, Nagatitan would have been recognisably similar to its more famous relatives Diplodocus and Brontosaurus. Massive body. Long tail. Very long neck. Small head. Constantly eating.

The scale is worth pausing on. Twenty-seven metres is roughly the length of a blue whale — the largest animal ever known to have lived on Earth. Twenty-seven tonnes is heavier than most modern semi-trucks fully loaded. This was, by any modern standard, an enormous animal. It would have moved slowly through the arid, semi-arid landscape of Cretaceous Thailand, crossing meandering rivers, browsing the tops of trees the way modern giraffes browse acacias.

Sethapanichsakul, the lead researcher, put the scale in a wonderful comparison: “Our dinosaur is big by most people’s standards — it likely weighed at least 10 tons more than Dippy the Diplodocus.” He also noted, in the interest of honesty, that Nagatitan is still dwarfed by the true giants of the sauropod world — animals like Patagotitan (60 tonnes) or Ruyangosaurus (50 tonnes). The Southeast Asian sauropods were huge, but they were not the largest known.

The 14th and possibly the last

Nagatitan is the 14th dinosaur species to be formally named in Thailand. The first, Siamosaurus suteethorni, was described in 1986. Since then, the country’s northeastern region has become one of the most fossil-productive parts of Asia — a hotspot for Mesozoic remains, thanks partly to its thick sedimentary rock formations and its comparatively dry, low-vegetation climate that helps preserve exposed bones from erosion.

Nagatitan came from Thailand’s youngest dinosaur-bearing rock formation, the Khok Kruat Formation. And here is where the discovery becomes quietly poignant.

The rocks that formed in this region after Nagatitan’s lifetime, in the later Cretaceous, were laid down as a shallow sea covered northeastern Thailand. Marine sediments don’t preserve terrestrial dinosaurs. As Sethapanichsakul put it in the published announcement: “Younger rocks laid down towards the end of the time of the dinosaurs are unlikely to contain dinosaur remains because the region by then had become a shallow sea. So this may be the last or most recent large sauropod we will find in Southeast Asia.”

Nagatitan may, in other words, be a horizon marker. There were almost certainly other large sauropods living in Southeast Asia in the later Cretaceous, all the way up to the mass extinction 66 million years ago. But their remains, if they were laid down at all, are underneath the sedimentary record of a vanished sea. The last large Southeast Asian sauropod humans will ever recover as a fossil may quite plausibly be this one.

What it changes

The wider scientific significance of Nagatitan goes beyond its size.

For years, Southeast Asia’s dinosaur record has been underappreciated compared to the more heavily studied fossil beds of North America, South America, Europe, and China. Most of what was known about Thailand’s sauropods came from small collections of scattered bones — not complete enough to describe as new species, not distinctive enough to add much to the global picture.

Nagatitan is different. It is, according to paleontologist Pedro Mocho of the Universidade de Lisboa, the most complete sauropod specimen ever recovered from the Khok Kruat Formation. It gives paleontologists an anchor point — a well-preserved, well-studied Southeast Asian sauropod they can compare other regional finds against.

Sethapanichsakul has been direct about his broader ambition. “My dream,” he said, “is to continue pushing to get Southeast Asian dinosaurs recognised internationally.”

Ten years after a farmer noticed some strange bones by a drying pond, that dream is a step closer. There is a life-sized reconstruction of Nagatitan now on display at the Thainosaur Museum in Bangkok. There is a research centre being established at the discovery site.

And somewhere in the geological record of Chaiyaphum Province, if the paleontologists are right, there may not be another one like it.