Scientists dig up Southeast Asia’s largest dinosaur in Thailand
By Will Dunham
May 14 (Reuters) – About 113 million years ago, along a winding river in a hot, arid region that is now Thailand, a herbivorous monster nearly 27 meters long grazed on treetops without much fear of predators due to its size. It was Nagatitan chaiyaphumensis, “the largest known dinosaur in Southeast Asia.”
Researchers have unearthed skeletal remains of Nagatitan, a member of the lineage of dinosaurs called sauropods, known to have a long neck, long tail, small head and four column-shaped legs.
Fossils of this Cretaceous dinosaur were first spotted by a villager in Chaiyaphum province, northeastern Thailand. Over several years, scientists then unearthed the bones of the spine, ribs, pelvis and legs, including a front leg bone – the humerus – measuring 1.78 meters long.
Based on the dimensions of its humerus and femur, the corresponding hind leg bone, researchers estimated Nagatitan’s body mass at between 25 and 28 tons. Its head and teeth were not among the fossils recovered, but researchers have a good idea of its dietary preferences based on other sauropods.
“Nagatitan was likely a large browser that focused on consuming high volumes of vegetation requiring little or no chewing, such as conifers and possibly seed ferns,” said Thitiwoot Sethapanichsakul, a paleontology doctoral student at the University of London and lead author of the research published Thursday in the journal Scientific Reports.
The climate was probably subtropical, with some forests, but also savannah and shrubland habitats. Nagatitan lived alongside various other dinosaurs as well as flying reptiles called pterosaurs. The rivers were teeming with crocodiles and fish, including freshwater sharks.
The largest predator in the ecosystem was a relative of the giant African dinosaur Carcharodontosaurus, probably around 8 meters long and around 3.5 tonnes.
“At that size, it was dwarfed by Nagatitan. At its full size, Nagatitan probably had very little to worry about in terms of predation,” Sethapanichsakul said.
Predators likely avoided attacking healthy adults of large sauropod species because of the danger of being crushed. But they may have targeted elderly or sick adults or vulnerable babies.
“Indeed, sauropods are known to have grown very quickly after hatching, and this is probably linked to the dangers of predation. The sooner sauropods could become larger, the safer they were, because they would have been more difficult to control,” said Paul Upchurch, a paleontologist at University College London and co-author of the study.
Sauropods comprised the largest land animals in Earth’s history. Nagatitan was huge by any standard, but not on the scale of some South American sauropods such as Argentinosaurus and Patagotitan which were 30 meters long.
The name Nagatitan refers to Naga, a serpent-like being in some Asian religious traditions and featured prominently in various Thai temples. In total, there are 14 named dinosaurs known in Thailand.
The names of several large sauropods include the word titan. Sethapanichsakul said it might be appropriate to call Nagatitan the last “titan” of Southeast Asia because the region became a shallow sea later in the Cretaceous, meaning no sauropods would live there anymore.
Nagatitan provides insight into the diversity of sauropods in the region. Few sauropods are known from Southeast Asia, and Nagatitan is the largest and youngest of them. Nagatitan belonged to a subgroup of sauropods that had bones with numerous internal air sacs and thin walls, features that made their skeletons lighter.
This group originated about 140 million years ago, reached a global distribution, and about 90 million years ago became the world’s only remaining sauropods, thriving until the age of dinosaurs ended 66 million years ago with an asteroid impact.
Nagatitan lived at a time when Earth’s atmospheric carbon dioxide levels were increasing, corresponding to high global temperatures.
“Sauropods appear to have become particularly large around this time, with gigantic forms living in South America, China, probably North Africa, and now, with Nagatitan, a fairly large form in Southeast Asia,” Upchurch said.
“This possible relationship between large body size and high climate temperatures is not fully understood, but it is likely that high temperatures impacted plant forage that was important to sauropods, which were very large herbivores. Nagatitan provides insight into the period leading to the eventual peak in body size and temperature around 10 to 15 million years later,” Upchurch said.
(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)
