A new species offers a clue to the boom of giant dinosaurs

Titans once towered over Thailand.

A research team led by National Geographic Explorer Sita Manitkoon has discovered a new long-necked dinosaur they estimate was over 88 feet long and weighed nearly 30 tons.

“Initial measurements of the bones excavated suggested that this could be the largest dinosaur ever found in Southeast Asia,” says Manitkoon, a paleontologist at Mahasarakham University in Thailand.

The telltale bones were uncovered in 2016 by a local man named Thanom Luangnan in Chaiyaphum Province, northeastern Thailand.

“He observed what he described as strange-looking rocks on the banks of a public pond,” says Manitkoon. Luangnan reported the findings to the country’s Department of Mineral Resources. The strange rocks, it turned out, were dinosaur bones, and when Manitkoon came upon them, he knew the creature must have been enormous.

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The researchers named the new species Nagatitan chaiyaphumensis after where it was found, and the giant serpent-like Naga of Southeast Asian folklore. The discovery, which was announced Thursday in the journal Scientific Reports, provides insight into how changes in ancient climate and vegetation opened the doors for gigantic dinosaurs to develop.

“This is the most complete sauropod specimen discovered from the Khok Kruat Formation,” says Pedro Mocho, a paleontologist at the Universidade de Lisboa in Portugal, who was not involved in the study. Until now, Mocho says, the big dinosaurs in Thailand were known only from bits and pieces of skeletons. The new find is substantially more complete, revealing a titanic dinosaur never seen in the country before.

Colossal Cretaceous sauropods

Nagatitan left behind a smattering of vertebrae, ribs, hip bones, and limb bones entombed in 113-million-year-old rock. Its right forelimb is longer than that of other, recently uncovered giant sauropods such as Patagotitan and Dreadnoughtus, though the dinosaur itself likely was not as big as those heavy hitters, which weighed an estimated 60 and 50 tons respectively.

The largest dinosaurs of all time were not each other’s closest relatives. Sauropod dinosaurs evolved their giant body sizes more than 30 times over the course of more than a hundred million years on at least six landmasses. Nagatitan became a giant independently of other huge dinosaurs from other periods and places, but its relationships and habitat suggest it lived at the beginning of a time conducive to enormous dinosaurs.

Nagatitan belonged to a group called the somphospondyli. These dinosaurs tend to have long forelimbs compared to other sauropods, as well as a wide stance, says Paul Upchurch, a paleontologist at the University College London and a coauthor of the study. The other differences would have been difficult to spot on the living animal, but these subtle cues identify the Nagatitans as a group of immense dinosaurs that spread far and wide some 110 to 120 million years ago during the Early Cretaceous.

How titans thrived

Environmental conditions in Cretaceous Thailand might explain why Nagatitan was so large.

During the time the dinosaur lived, Thailand was closer to the equator than it is today. Clues found in the same formation in which Nagatitan was buried indicate that the region was covered by relatively open, slightly dry shrublands. Earth was in a hothouse state, and recent research has suggested that big sauropod dinosaurs thrived under such conditions. Humongous herbivores could easily and efficiently travel through the woodlands, browsing on trees and nibbling plants like horsetails and ferns down low. Their feeding and trampling of the soils also kept such habitats more open and savanna-like rather than thickly forested.

Nagatitan represents the beginning of this size boom. When the researchers looked at other giant sauropods from Asia for comparison, they found that the dinosaurs got even bigger during the warm Cretaceous years following the time of Nagatitan.

“Sauropods such as Ruyangosaurus, nearly 60 tons, are among the largest from Asia during the Cretaceous,” Manitkoon says. They add support to the idea that warm, open, and relatively dry habitats created ideal conditions for sauropods to evolve to giant sizes.

The overall picture is complex, says Mocho. Sauropod dinosaurs both expanded and shrank in size at different times and places.

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“Savannah-like ecosystems are known to favor the development of megaherbivore faunas, and it would not be surprising if environmental factors were related to sauropod gigantism,” he says.

The interplay between large herbivores like elephants and their habitats today could help researchers better perceive similar patterns in the fossil record.

“It seems a little odd that sauropods were able to cope with higher temperature conditions,” says Upchurch, as large bodies are harder to cool down and retain heat more readily.

But sauropod anatomy likely allowed the dinosaurs to work against expectations.

The long necks of the dinosaurs, Upchurch says, increased the surface area from which they could shed heat. Their complex air sac system would also have helped them dump body heat as they exhaled. When habitats shifted to warm woodlands, full of vegetation at browsing height, the evolutionary gifts that sauropod dinosaurs already had allowed them to balloon in size, as they were well equipped to handle the heat.

“The discovery of Nagatitan and its giant relatives in Asia indicates that these dinosaurs had evolved to such enormous sizes since the early Cretaceous, a successful survival mechanism,” Manitkoon says.

The fossil record shows that from the time of Nagatian until the asteroid strike, dinosaur titans repeatedly evolved and grew large when conditions were just right.