Meet Nagatitan: Largest dinosaur ever discovered in Southeast Asia

A front leg bone nearly as tall as a person lay buried beside a pond in northeastern Thailand. It was part of a skeleton so large it belonged to an animal about 27 meters long and weighing roughly 27 tonnes.

That animal now has a name: Nagatitan chaiyaphumensis, a newly described long-necked plant-eater from the Early Cretaceous. Researchers say it is the largest dinosaur yet identified in Southeast Asia. The fossils were found in Chaiyaphum Province. They come from Thailand’s Khok Kruat Formation, the youngest dinosaur-bearing rock unit known in the country.

The new species belonged to the sauropods, the immense, long-tailed herbivores that include famous names such as Diplodocus and Brontosaurus. In this case, the team concluded that Nagatitan was part of a narrower Asian branch called Euhelopodidae. This is a group whose family ties have long been debated.

For Thailand, the find adds another important piece to a fossil record that has grown steadily over the past four decades. It is the 14th dinosaur to be formally named from the country.

The bones were first noticed by a local resident in 2016 during the dry season, when falling water levels exposed a bone bed along the side of a communal pond at Ban Pha Nang Sua. Fieldwork ran from 2016 to 2019. Moreover, more excavation followed in 2024.

Researchers recovered four dorsal vertebrae, four sacral vertebrae, five ribs, a right humerus, part of the pelvis, a pair of pubes and most of a right femur. They also found fragments. Because the bones were similar in size, found close together and did not duplicate one another, the team concluded they most likely belonged to one individual.

That mattered, because the remains came from Thailand’s youngest fossil-bearing Mesozoic formation. Lead author Thitiwoot Sethapanichsakul, a PhD student at UCL Earth Sciences, called Nagatitan “the last titan” of Thailand.

“That is because it was discovered in Thailand’s youngest dinosaur-bearing rock formation,” he said. “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.”

The name reflects both place and legend. “Naga” refers to the serpent-like being in Thai and wider Southeast Asian folklore, often linked with water, while “titan” invokes the giants of Greek mythology. The species name points back to Chaiyaphum, where the fossils were unearthed.

The team identified the animal as a new genus and species from a specific mix of skeletal traits in the spine, pelvis and limbs.

Some of the most distinctive features came from the back bones. The dorsal vertebrae preserved unusual combinations of ridges, hollows and spine shapes, including triangular projections on the upper part of the neural spines that the researchers said have not been seen in any other sauropod. The humerus also stood out. It was complete, 1.78 meters long, and had a rounded upper outer corner unlike the squarer form seen in many related species.

The femur, though incomplete, was estimated to have measured about 1.9 to 2 meters in life.

Those measurements helped the authors estimate the dinosaur’s overall size at around 27 meters in length and about 27 tonnes in body mass. That would make it substantially larger than Phuwiangosaurus, another Thai sauropod. However, it was close in size to Tangvayosaurus from Laos. It still fell well short of true giants such as Patagotitan and Ruyangosaurus, which have been estimated at around 60 and 50 tonnes respectively.

Sethapanichsakul put the scale in everyday terms. “Our dinosaur is big by most people’s standards,” he said. “It likely weighed at least 10 tonnes more than Dippy the Diplodocus (Diplodocus carnegii). However, it is still dwarfed by sauropods like Patagotitan (60 tonnes) or Ruyangosaurus (50 tonnes).”

The world Nagatitan lived in looked very different from modern Thailand. During the Aptian to Albian stages of the Early Cretaceous, the Ban Pha Nang Sua site was part of a meandering river system in a semi-arid environment.

The sediment layers at the site suggest cycles of river deposition. Other fossils from the area show the habitat supported fish, freshwater sharks, turtles and crocodile relatives. Teeth from large meat-eating dinosaurs were also found nearby, including carcharodontosaurians and spinosaurids.

So this giant herbivore was not alone.

It shared its landscape with smaller plant-eaters such as iguanodontians and early ceratopsian relatives, while pterosaurs hunted fish overhead. The researchers argued that sauropods may have done well in such dry to semi-dry settings. In part, this could be because their long necks and tails gave them extra surface area that could help shed heat.

The formation itself has drawn growing attention because its vertebrate fauna resembles that of similarly aged rocks in Laos and southern China. Yet the new study found no clear sign that Nagatitan was especially close to the known sauropods from China’s Xinlong Formation. It did, however, sit within a broader Asian sauropod story.

The authors tested Nagatitan against a large dataset of sauropod anatomy and ran two phylogenetic analyses. Both placed it within Euhelopodidae, an early-diverging subgroup of somphospondylan sauropods known mainly from Asia.

That result matters because the internal relationships of these animals have remained unsettled. The fossil record is patchy, and some named species are incomplete or poorly described. In Thailand and Laos especially, the relationships between Nagatitan, Phuwiangosaurus and Tangvayosaurus may shift as older specimens are reexamined and new ones are described.

The researchers also raised a note of caution. Current character scoring for Phuwiangosaurus and Tangvayosaurus was not based on new first-hand study in this project, and the Lao species still lacks a full modern description. The Thai material, meanwhile, may include fossils that have been grouped too broadly under older names.

That makes Nagatitan important not just because it is large, but because it adds a better described specimen to a region where major questions remain open.

Professor Paul Upchurch of UCL Earth Sciences said the work grew out of a new collaboration between University College London (UCL), Mahasarakham University, Suranaree University of Technology and Sirindhorn Museum in Thailand. 3D scanning and printing helped the team study the bones without constant travel.

“We have had a long-standing interest in the evolution of these gigantic plant eaters and have good collaborative links with researchers around the world,” he said. “It is great to work with Thai colleagues and start to get insights into what was happening in Southeast Asia during the Jurassic and Cretaceous.”

Sethapanichsakul framed the discovery in more personal terms: “I’ve always been a dinosaur kid. This study doesn’t just establish a new species but also fulfils a childhood promise of naming a dinosaur.”

The discovery gives Southeast Asia a larger role in the global story of sauropod evolution. It strengthens the case that the region was home to very large plant-eating dinosaurs during the late Early Cretaceous, and not just smaller or poorly known forms. It also adds weight to the idea that Asian titanosauriforms grew bigger during the middle part of the Cretaceous.

Just as important, the work highlights how much remains undescribed in museum collections. Sethapanichsakul said Thailand holds a large number of sauropod fossils that still have not been formally studied. Some may represent additional new species.

That means Nagatitan may be less an isolated giant than the first clear sign of a broader, still partly hidden dinosaur record in the region.

Research findings are available online in the journal Scientific Reports.

The original story "Meet Nagatitan: Largest dinosaur ever discovered in Southeast Asia" is published in The Brighter Side of News.

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